<%BANNER%>

Solids Accululation Rates for Onsite Sewage Treatment and Disposal Systems: A Focus on Charlotte County, Florida

HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Review of literature
 Methods
 Results and discussion
 Summary and conclusions
 Recommendations for future...
 Appendices
 References
 Biographical sketch
 

PAGE 1

SOLIDS ACCUMULATION RATES FOR ONSITE SEWAGE TREATMENT AND DISPOSAL SYSTEMS: A FOCUS ON CHARLOTTE COUNTY, FLORIDA By TRISHA LURTZ HOWARD A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2003

PAGE 2

Copyright 2003 by Trisha Lurtz Howard

PAGE 3

This document is dedicated to the Lord Je sus Christ, my Lord and Savior, who brought me through my weakness with his perfect love. And this document is also dedicated to my loving husband.

PAGE 4

iv ACKNOWLEDGMENTS I would like to thank to the Charlotte C ounty Department of Health, the Florida Department of Environmental Protection, and the United States Environmental Protection Agency for the opportunity to work on this project. I would also like to thank Dr. Alexandre Trinidad in the Department of Statistics and Dr. Yong-Song Joo from IFAS Statistics for their willingness to volunteer their time, and Dr. Gary Stevens from the BCL for running the statistical analysis of th e data. I am grateful to Mr. Paul Booher from the FDOH for the information on tank manufacturers and schematic information. This study would not have been possible without the willingness and cooperation of the residents in Charlotte County to allow us to study th eir systems and provide their household practices information. Finally, I wish to give than ks to Mr. Robert Vincent, Mr. Bud Wimer, and Mr. Jeffrey Tompkins for their vigilance and guidance throughout this project. Most of all I would like to thank my fam ily and friends. I would like to give a special thank you to my brother-in-law, Thomas and my dear friend, Liz, who helped me through the trials of writing. And, of course, I would like to thank my parents for preparing me for college and my husband for loving me through this research.

PAGE 5

v TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES........................................................................................................... viii LIST OF FIGURES .............................................................................................................x ABSTRACT...................................................................................................................... x ii CHAPTER 1 INTRODUCTION........................................................................................................1 A Case for Standardized Management of OSTDSs......................................................2 Evidence of Failure................................................................................................2 Failure Reasons .....................................................................................................4 System Failure Impacts on Surrounding Area.......................................................5 Charlotte County, Florida.............................................................................................6 Research Scope.............................................................................................................9 2 REVIEW OF LITERATURE.....................................................................................11 OSTDS Design and Operation....................................................................................11 Septic Tank Design and Operation......................................................................11 Septic tank design.........................................................................................11 Septic tank operation....................................................................................14 Drainfield Design and Operation.........................................................................16 Drainfield design..........................................................................................17 Drainfield operation .....................................................................................18 OSTDS Maintenance..................................................................................................20 Annual Inspection................................................................................................21 Maintenance Pumping.........................................................................................21 EPA Management Guidelines .............................................................................22 Previous Solids Accumulation Rate Research............................................................23 Discussion of Prior Studies .................................................................................23 United States Public Health Service.............................................................23 Bounds Study ...............................................................................................26 Moore Study.................................................................................................28 Comparison of Pump Out Frequencies................................................................29

PAGE 6

vi 3 METHODS.................................................................................................................32 Objectives ...................................................................................................................32 Task 1: Identification of Relevant Variables..............................................................33 Wastewater Characteristics .................................................................................33 System Design.....................................................................................................35 Surrounding Environment ...................................................................................35 Task 2: Selection and Recruitment of Participants.....................................................36 Subtask 2A: Participant Selection .......................................................................37 Location of systems in Charlotte County.....................................................37 Identification of OSTDS density by soil type ..............................................37 Random selection of potential participants ..................................................37 Subtask 2B: Recruiting of Participants................................................................38 Newspaper article.........................................................................................38 Mailing campaign.........................................................................................38 County fair....................................................................................................40 Subtask 2C: Division of Recruits into Phase 1 and Phase 2 of the Study...........40 Subtask 2D: Data Collection and Databasing .....................................................41 Initial survey.................................................................................................41 Follow-up survey..........................................................................................42 Permit information .......................................................................................42 Inspection information .................................................................................42 Height measurements ...................................................................................43 Databasing of all variables collected............................................................43 Task 3: Calculation of Solids Accumulation..............................................................43 Subtask 3A: Determination of Tank Dimensions................................................44 Subtask 3B: Calculation of So lids Volumes in Each Tank .................................46 Subtask 3C: Calculation of Accumulation Rates ................................................48 Subtask 3D: Assessment of Trends in Accumulation .........................................48 Task 4: Interpretation of Phas e I and Phase II Model Results....................................49 Subtask 4A: Assess Sample Size.........................................................................49 Subtask 4B: Assessment of Correlations.............................................................50 Subtask 4C: Assessment of Model Results .........................................................50 4 RESULTS AND DISCUSSION.................................................................................52 Task 1: Identification of Relevant Variables ..............................................................52 Task 2: Selection and Recr uitment of Participants ....................................................55 Subtask 2A: Selection of Potential Participants ..................................................55 Subtask 2B: Recruit Participants.........................................................................56 Subtask 2C: Separation of Recr uits into Phase 1 and 2.......................................59 Subtask 2D: Data Collection and Databasing .....................................................60 Task 3: Calculation of Solids Accumulation..............................................................62 Subtask 3A: Calculation of Tank Dimensions ....................................................62 Subtask 3B: Calculation of Solid Volumes Septic Tank.....................................62 Subtask 3C: Calculation of Accumulation Rates ................................................63 Accumulation rate per system......................................................................64

PAGE 7

vii Accumulation rate per person ......................................................................65 Subtask 3D: Trends in Accumulation..................................................................66 Accumulation trends during the first year....................................................66 Accumulation trends in relation to people and septic tank volume .............67 Task 4: Interpretation of Phas e 1 and Phase 2 Model Results....................................71 Subtask 4A: Assess Sample Size.........................................................................71 Subtask 4B: Development of Correlations..........................................................74 Sludge accumulation rate correlations .........................................................74 Scum accumulation rate correlations ...........................................................75 Subtask 4C: Development of Model Results.......................................................77 5 SUMMARY AND CONCLUSIONS.........................................................................80 6 RECOMMENDATIONS FOR FUTURE WORK.....................................................84 Identification of Relevant Variables...........................................................................84 Selection, Recruitment, and Monitoring of Participants ............................................85 Participant Selection............................................................................................85 Recruiting Participants ........................................................................................85 Division of Recruits for Two Groups..................................................................86 Data Collection...........................................................................................................86 Calculation of Solids Accumula tion and Model Development..................................87 APPENDIX A CONTENTS OF PACKAGE INITIA LLY MAILED TO PARTICIPANTS ............88 B INTIAL AND FOLLOWUP SURVEYS ...................................................................92 C DESCRIPTION OF METHOD USED TO DIVIDE PARTICIPANTS INTO PHASE 1 AND 2 GROUPING ..................................................................................98 D TANK DIMENSIONS. .............................................................................................102 Manufactured Tank Dimensions...............................................................................102 Method 1 Tank Dimension Calculation....................................................................102 Method 2 Tank Dimension Calculations ..................................................................103 LIST OF REFERENCES.................................................................................................105 BIOGRAPHICAL SKETCH ...........................................................................................110

PAGE 8

viii LIST OF TABLES Table page 2-1 Residential Estimated Sewage Flow* ......................................................................14 2-2 Minimum Effective Septic Tank Capacities ............................................................14 2-3 USPHS Septic Tank Years of Service (Weibel et al., 1949)....................................24 2-4 USPHS Accumulation Means a nd Medians (Weibel et al., 1949)...........................24 2-5 Total per Capita Sludge and Scum Accumulation (Weibel et al., 1949) .................26 2-6 Moore Study (2002) Distribu tion of Years of Service.............................................28 2-7 Moore Study (2002) Scum and Sludge Accumulation Trends ................................29 2-8 Summaries of Prior Studies......................................................................................30 4-1 Potential Performance Factors Descri bing Wastewater Quality and Hydraulics.....54 4-2 Potential Performance Factors De scribing System Design and Condition..............55 4-3 Potential Performance Factors Describing Surrounding Environment....................55 4-4 Most Populated Soils (with Largest Nu mber of OSTDSs) in Charlotte County..56 4-5 Recruitment Results .................................................................................................58 4-6 Distribution for Quantitative of House hold Characteristic for All Recruits ............60 4-7 Distribution for Qualitative of Hous ehold Characteristics for All Recruits.............60 4-8 Frequencies for Each Level of Household Characteristics for Each Phase...............61 4-9 Scum Volume 6 and 12 Months After Pump out.....................................................63 4-10 Sludge Volume 6 and 12 Months After Pump out...................................................63 4-11 Total Solids Volume 6 and 12 Months After Pump out...........................................63 4-12 Scum Accumulation Rates .......................................................................................64

PAGE 9

ix 4-13 Sludge Accumulation Rates .....................................................................................64 4-14 Total Solids Accumulation Rates.............................................................................64 4-15 Scum and Sludge Accumulation Rate Data Determined Using Linear Fits ............65 4-16 Scum per Person Accumulation Rate.......................................................................65 4-17 Sludge per Person Accumulation Rate.....................................................................65 4-18 Total Solids per Pe rson Accumulation Rate ............................................................65 4-19 Accumulation Rates of Solids per Person Determined Using Linear Fits ...............66 4-20 Solids Volume Change from 6 months to 12 months ..............................................66 4-21 Solids Accumulation Rate Cha nge from 6 months to 12 months ............................67 4-22 Accumulation Rates Based on the Number of People in the Home.........................68 4-23 Accumulation Rate Based on Septic Tank Volume.................................................69 4-24 Accumulation Rate based on Septic Tank Capacity ................................................71 4-25 Significant Sample Size Values ...............................................................................73 C-1 Quantitative Data Description................................................................................100 C-2 Variable Phase Distribution...................................................................................101 D-1 Manufactured Tank Dimensions............................................................................102 D-2 Method 1 Dimension Calculations..........................................................................103 D-3 Method 2 Ratios and Dimensions ..........................................................................103 D-4 Method 2 Calculated Dimensions ..........................................................................104

PAGE 10

x LIST OF FIGURES Figure page 1-1 OSTDS Locations in Charlotte County......................................................................7 1-2 Average Number of New Systems Installed from 1971 to 2001 ...............................8 2-1 A Multiple Chamber Septic Tank Schematic...........................................................13 2-2 Septic Tank Width Profile s (a) V-bottom (b) Taper ................................................13 2-3 PHS Rate of Scum & Sludge Accumulation............................................................25 2-4 Bounds Study Volume of Total Solids For Eight Years ..........................................27 3-1 Selected Systems in Mid-County 2 Basin per Soil Type .........................................39 3-2 V-bottom Septic Tank Schematic with Dimensions ................................................45 3-3 Taper-Side Septic Tank Schematic with Dimensions..............................................45 3-4 Height Dimensions for Liquid Height (HL), Scum Height (hsc), and Sludge ..........47 4-1 Divisions of Performance Variable s into the Three Characteristic Groups.............53 4-2 Selected Homes having OS TDSs within Mid-County-2..........................................57 4-3 Accumulation Rate Trends Based on Number of People in the Home ....................69 4-4 Accumulation Rate Trends Based on Septic Tank Volume.....................................70 4-5 Accumulation Rate Trends Based on Septic Tank Capacity....................................72 4-6 Scatter Plots for Sludge A ccumulation Rates at 6 Months ......................................78 4-7 Scatter Plots for Scum A ccumulation Rates at 12 Months ......................................79 A-1 Flier (a) front (b) back..............................................................................................89 A-2 Consent Form Page 1 ...............................................................................................90 A-3 Consent Form Page 2 ...............................................................................................91

PAGE 11

xi B-1 Initial Survey Page 1 ................................................................................................93 B-2 Initial Survey Page 2 ................................................................................................94 B-3 Initial Survey Page 3 ................................................................................................95 B-4 Follow-up Survey Page 1 .........................................................................................96 B-5 Follow-up Survey Page 2 .........................................................................................97 C-1 Number of Occupants pe r Home Frequency Chart..................................................98 C-2 Occupancy in Home during the Year Frequency Chart ...........................................99 C-3 Washing Machine Loads per Week Frequency Chart..............................................99 C-4 Dishwasher loads per Week Frequency Chart .......................................................100

PAGE 12

xii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering SOLIDS ACCUMULATION RATES FOR ONSITE SEWAGE TREATMENT AND DISPOSAL SYSTEMS: A FOCUS ON CHARLOTTE COUNTY, FLORIDA By Trisha Lurtz Howard December 2003 Chair: Angela S. Lindner Major Department: Environmental Engineering Sciences In 1999, 24.1% of American households and more than 60 million people used onsite sewage treatment and disposal syst ems (OSTDSs) for domestic wastewater treatment, with Florida consistently containing the largest number of systems than any other state. For example, in 1990, Florid a was reported as having1.56 million OSTDSs. In Charlotte County, Florida, approximat ely 24,000 systems were installed before 1983, and, as of 1998, nearly 40,000 systems were in place, with 82% of these in residential areas. As these systems age, they may eventually fail if not maintained. A survey conducted by the U.S. Census Bureau ( 1997) estimated that 403,000 homes experienced system failure within the 3-month survey period, and 31,000 of these homes were reported to have four or more breakdowns during this period. Studies reviewed by the U.S. Environmental Protection Agency (U.S. EPA) cite failure rates ranging from 10-

PAGE 13

xiii 20%. System failure surveys typically do not include systems that might be contaminating their surrounding environment, as these failures are not always obvious. The primary goal of this study was to better understand the underlying factors (social, geographical, system design, etc.) that impact system performance. The ultimate goal of this study was to provide CCDOH with a list of factors that potentially hamper the ability of the region’s OSTDSs to perf orm effectively. The primary methods to determine these factors invol ved a combination of recrui ting for participants, data gathering using surveys, inspections, and permits, and multiple linear regression (MLR) analysis. Two hundred twenty-one Charlo tte County residents were recruited for participation in this study. MLR analysis related solids accumulation rates (as dependent variables) with the performa nce variables collected in the data gathering phases. Those performance variables that were id entified as having the greatest impact on solids accumulation were relate d to wastewater generating ac tivities in the household and flooding frequencies. The scum accumulation rate significantly related to the use of garbage disposals, the disposal of food pa rticles while rinsing dishes, the washing machine capacity, and the dishwasher detergent. The sample size was limited in yielding significant results for the sludge accumulation rate. Despite the inability of cons tructing statistically robust multiple linear correlations, this study yielded a greater understanding of the importance of adopting better household practices that result in less potential for OSTDS failure. By establishing community outreach programs for OSTDS owners, CCDOH can prevent risk to the environment and public health by ensuring that Charlotte County’s systems do not fail and intrude on surrounding surface waters.

PAGE 14

1 CHAPTER 1 INTRODUCTION Results from the U.S. Census in the past 20 years indicate that use of onsite sewage treatment and disposal systems (OSTDSs) is a common method of managing household wastewater in the United States. In 1999, approximately twenty-three percent (26,051,000) of all of the nation’s homes us ed OSTDSs (U.S. Census Bureau, 2003), including one-third of newly constructed homes and one-half of all mobile homes. Over 50% of OSTDSs in the United States we re found to exceed 30 years of service, surpassing the intended 20-30 years of useful life of these systems. Florida possesses the largest number of OSTDSs than any other state in nation with 1.56 million in 1999 (U.S. Census Bureau, 2003). In 1987, Florida exceeded 60,000 permits for new systems annually (Ayres Associates, 1987). As the popul ation in Florida incr eases along with the number of households using OSTDSs for wa stewater management, there is an urgent need to address factors that affect the perfor mance of these systems in order to minimize and ultimately prevent negative public and environmental health impacts. This report focuses on the results of a study, funded by the Charlotte County Department of Health (CCDOH), that began in July 2001. The overall goal of this work was to identify the most significant human a nd environmental factors that have potential to cause an OSTDS to fail, and, with these results, to allow CCDOH to recommend best management practices to its re sidents. Chapter 1 of this report provides an overview of this project with a descrip tion of Charlotte County and the research scope. Chapter 2 presents a thorough literature review of all research to date concerning OSTDSs,

PAGE 15

2 including detailed descripti ons of their design, normal maintenance, and wastewater characteristics. Chapter 3 presents the met hods used in this study, and Chapter 4 presents the results of this work. Chapter 5 presen ts the conclusion of this study, and Chapter 6 presents recommendations for best practices in OSTDS management and for extending this study. A Case for Standardized Management of OSTDSs Homeowners typically have the sole re sponsibility for mana ging and maintaining OSTDSs (U.S. EPA, 2002; Laak and Crat es, 1978). During a 3-month period in 1995, 1.57% of the total systems in the nation experienced system failures, with 31,000 of those homes reporting four or more OSTDS failure s during that same period (U.S. Census Bureau, 1997). During a 3-month period in 1999, 1.44% of the total systems in the nation experienced system failures, with 27,000 of those homes reporting four or more OSTDS failures during that same period (U .S. EPA, 2002). Despite an increase of systems, the number of reported failur es decreased from 1995 to 1999, possibly indicating improved management of the system s. The OSTDS failure rate throughout the U.S. ranges from 10-20% of all systems (U.S. EPA, 2000a). Evidence of Failure An OSTDS is considered to have failed when it no longer treats wastewater to dischargeable conditions. Monitoring for system failure is often difficult because both wastewater treatment and discharge occur unde rground. A wide variety of criteria exist to signal system failure, and a brief description of these failure characteristics is presented below. Class I. The first type of failure symptoms, kno wn as Class I, is the reentry of raw sewage back into the house, commonly te rmed a “sewage backup” and immediately

PAGE 16

3 noticed by the homeowner (Brown, 1998). The raw sewage returns through the drains or toilets (Vogel and Rupp, 1999; Brown, 1998) from either blockage in the pipes connecting to the septic tank or the septic ta nk approaching full capacit y for solid storage. A slow flushing toilet or empt ying drain can be the first signs of a blockage in the pipes or a near-full septic tank (Vogel and Rupp, 1999). Class II. The second group of failure symptoms, cal led Class II, is raw or partially treated sewage surfacing in th e yard (Brown, 1998). In this class of failure symptoms, the toilet and other water-using facilities us ually function properl y, but untreated or poorly treated sewage surfaces in the yard or seeps along the surface of the ground near the system (Vogel and Rupp, 1999; Brown, 1998). Evidence of a system failure for class of symptoms is apparent when lush green grass flourishes over the system despite no sewage surfacing. Excessive growth of plant materials indicates an excessive amount of nutrient-rich liquid moving up thr ough the soil (Vogel and Rupp, 1999). Class III. The third type of failure characteristics, called Class III, is the decline in water quality while the household plumbing and dr ainfield seem to be working perfectly without evident odors or exce ss wetness around the drainfield (Brown, 1998). Failures of this type result in a decline in the quality of groundwater and/or surface water; however, because there is no other obvious evidence, hom eowners may be skeptical that this is a result of their systems (Brown, 1998). The build up of aquatic weeds or algae in lakes or ponds adjacent to a homeowner’s system is indication of nutrient overload from failing OSTDSs (Vogel and Rupp, 1999). Class IV. The final evidence of failures is a long-term, gradual environmental degradation (Brown, 1998). Ther e is little, if any, scientif ic evidence that ground water

PAGE 17

4 or surface water is being degraded at a rate lik ely to be a problem for the current or next generation of residents. However, modeling and long-term monitoring indicate that very gradual environmental degradation may result fr om improper septic system practices at a particular home site, in a neighborhood, or in a region. Of all the classes of system failure, this one is the most difficult to prove (Brown, 1998). Failure Reasons Failing systems are often left unnoticed unt il Class I-IV evidence of failure (as previously described) becomes bothersome to the homeowner or apparent to the regulatory agency. System failures are typica lly the consequence of several factors, but the most common reason is system mismanag ement. OSTDS failures can be grouped into three possible causes: the system lo cation, the system design and condition, or management of the system by the homeowner. The system location can jeopardize the performance of an OSTDS depending on the OSTDS density in the region, the presence of effective drainage, and elevation of the seasonal high groundwater table. A high density of OSTDSs decrease the so il’s natural capacity to purify wastewater (Yates, 1985), while effective drainage (via permeable subsoils) is critical to prevent liquids from entering the septic tank from a flooded drainfield or leaky tank (Vogel and Rupp, 1999; Brown, 1998; Bounds, 1996; Bell, 1977). High groundwater elevation results in an insufficient unsatur ated soil depth under the drainfield, which must be maintained when the groundwater elevati on is at its highest elevation (Brownand Bicki, 1987). System deterioration and under-design can also prev ent proper functioning. System failures can be minimized through in formed planning and installation of the system (Brown, 1998). Deterioration of a sy stem is caused by root growth in pipes,

PAGE 18

5 crushed drainfield pipes, poor original design, or poor insta llation. Septic tanks, suffering from corrosion or root infiltration, allow wate r outside of the system to enter, and the resulting hydraulic overload of the tank cause s sewage to return to the home or to surfaces in the nearby yard (U.S. EPA, 1980). The daily habits of the occupants, such as water use and disp osal activities, can cause a system with proper siting and excelle nt condition to fail. Management of an OSTDS, including use and maintenance practices, is the sole responsibility of the owner. Therefore, for an owner to avoid the most commonly reported failure, hydraulic overloading, he/she must routinely perfor m tasks, such as monitoring tank residual buildup, scheduling pumping, ensuring proper flow distribution, checking pumps and float switches, inspecting f iltration media for clogging, a nd performing monitoring and maintenance tasks (U.S. EPA, 2002). Unfort unately, most homeowners have a limited knowledge of OSTDS management practices, thus increasing th e risk of their system to reach overcapacity and, ultimately, leading to clogged drainfields (U.S. EPA, 2000a; Vogel and Rupp, 1999; Bell, 1977). System Failure Impacts on Surrounding Area OSTDS failures can result in endangering public and environmen tal health, not to mention high costs for system repairs. Improper maintenance can yield undesirable odors, mosquito breeding areas, repair or replacement, condemnation of residence, groundwater contamination, and the spreads of disease associated with sewage (Bicki, 1989). Failed systems, mostly caused by improper maintenance, are the third most common source of groundwater contaminati on (Robertson et al., 1991; Canter and Knox, 1985; Yates, 1985), and sewage has been attrib uted to being the source of nearly one third of the miles of contamination observed along the U.S. ocean shoreline (U.S. EPA,

PAGE 19

6 1996a; LaPointe and Clark, 1992; Weiskel and Howes, 1992). In 1996, the Clean Water Needs Survey revealed that more than 500 co mmunities in the nation have public health problems caused by failed systems (U.S. EPA, 1996b). Over half of the waterborne disease outbreaks in the nation are from c onsuming contaminated groundwater. The contaminated groundwater is most frequen tly contaminated with OSTDS effluents (Yates, 1985). Charlotte County, Florida Charlotte County was the subject of this st udy. Located approximately 100 miles south of Tampa on the southwest coast of Florida, Charlotte County is 894 square miles in area with the Gulf of Mexico serving as its west border. 705 square miles of Charlotte County is land and the rest is water. In the 1960s and 1970s, 68 square miles were subdivided into several hundred thousand -acre lots. The maximum elevation of the land is 35 feet above sea level, approximately 13 miles inland from the Charlotte Harbor, the second largest estuarine harbor in Florida (also in Charlotte County). The county has over 300 miles of navigable and drainage canals with nearly 300,000 waterfront lots. The buildable areas, developed and undeveloped, have a seasonal high groundw ater table within one inch of the ground surface. Figure 1-1 illustrates the location of homes served by OSTDSs and sewer with in Charlotte County. As of 1998, just fewer than 40,000 OSTDSs existed in Charlotte County with 82% residential and 18% commercial or institutional and in industrial zones. Approximately 24,000 systems were installed before 1983. The median age of systems in 1998 was 12 years. Charlotte County experienced rapi d growth between the years of 1977 and 1990 with the peak of installations in 1978.

PAGE 20

7 Figure 1-1 OSTDS Locations in Charlotte County .

PAGE 21

8 Figure 1-2 Average Number of New System s Installed from 1971 to 2001 in Charlotte County (Florida Depart ment of Health, 2003) Charlotte County has eleven major municipal wastewater treatment plants (MWWTP), all permitted at or above 50,000 GPD and 2 larger MWWTP permitted above 2 MGD. The county also has 36 sm aller MWWTP with a loading capacity of 50,000 to 75,000 GPD. The high count of OSTDSs used in the county is because of a lack of existing infras tructure (Vincent, 1998). In the mid-1990s, the Charlotte County Commission was prepared to begin a utility expansion to connect most of Port Charlo tte to sewer. The residents opposed the expansion mainly because of the anticipated cost and the lack of evidence that the OSTDSs were a source of pollution in the c ounty. The cost of the expansion is $8,000 per property expected to be paid by the pr operty owner, not incl uding the monthly water bill. With one-third of the population over 65 and one of the highest median ages of 58, the community of Charlotte Count y attracts citizens fo r its excellent retirement lifestyle. In 1999, there were 140,000 year-round resident s and 60,000 winter resi dents visiting 4-6 0 500 1000 1500 2000 2500 19701975198019851990199520002005YearNumber of New OSTDS Installations

PAGE 22

9 months a year. The median income is $42,000 a year, and the median home price is $74,000. Research Scope This project sought a novel approach to the study of OS TDSs in Charlotte County – by better understanding the underl ying factors (social, geogra phical, system design, etc.) that impact system performance, a predic tive model could be developed to enable prevention of problems leading to system failu res. The objective of this research by the University of Florida was to determine the underlying factors that correlate with sludge and scum accumulation and to develop, if po ssible, an accumulation model of sludge, scum, and total solids using data measured durin g one year of service. The specific tasks of this project are the following: 1. Identify relevant variables that may impact OSTDS performance. 2. Collect specific information concerning relevant performance variables from a selected population of Char lotte County OSTDS owners. 3. Create a model to predict accumulation that will aid in the creation of a pump out schedule specific to the individual OSTDS. 4. Interpret the model results that will, in turn, allow CCDOH to establish recommended best management practices for OSTDSs. The United States Environmental Prot ection Agency (U.S. EPA), Florida Department of Environmental Protection (F DEP), and the Charlotte County Department of Health (CCDOH) sponsored this research. More specifically, th is project was funded in part by a Section 319 Nonpoint Source Ma nagement Program Implementation grant from the U.S. EPA through an agreem ent/contract with the Nonpoint Source Management Section of FDEP.

PAGE 23

10 By completion of these tasks, perfor mance factors that influence solids accumulation during the first year of servic e of an OSTDS were identified and best management practices determined, thus ai ding in preventing further environmental deterioration caused by these systems and a dding to the continuously growing body of knowledge on trends in solids accumulati on and required pumping frequencies.

PAGE 24

11 CHAPTER 2 REVIEW OF LITERATURE OSTDS Design and Operation OSTDSs provide effective wastewater tr eatment when properly sited, designed, and managed. A conventional OSTDS consists of a septic tank and a drainfield. An OSTDS has many advantages over a wastewater tr eatment plant. OSTDSs require minimum energy and technology, while also being low in cost. Unlike a wastewater treatment plant, an OSTDS requires no operators, no movi ng parts, little scheduled maintenance, and produces less sludge (Laak and Crates, 1978). However, wastewater treatment plants have better management and mainte nance when compared with OSTDSs. Septic Tank Design and Operation Quality septic tank design ensures proper operation and treatment of wastewater. Septic tanks must be designed to promote th e separation of solids from the wastewater effluent. The septic tank must also be at adequate capacity to guarantee retention of effluent to allow settling and storage of the settled solids. The stored solids are then subjected to partial tr eatment by degradation. Septic tank design Septic tanks are designed to prevent failure and increase longevity of a drainfield by preventing solids from exiting. A septic ta nk has the following components: entrance and exit baffles, a manhole, and possibly an in terior wall (Figure 21). The entrance and exit baffles are designed to allow wastewater to enter the septic tank and clarified effluent to leave without stored solids exiting. Like a settling chamber, the entrance and exit

PAGE 25

12 baffles are located on the walls of furthest di stance to allow adequate retention time and settling of solids. The manhole allows access to monitor the retained solids, to pump septage when solids reach capacity, and to in spect septic tank condi tions. An interior wall is used to divide the septic tank into two separate chambers. Multiple chambers reduce the amount of solids that can exit when the tank is hydraulical ly overloaded. The Florida Department of Health regulates the design of septic tanks through the Florida Administrative Code of Standa rds. Major criteria for sept ic tank design by the Florida Department of Health are as follows: must be watertight (64E-6.002(49)), can have a single or double compartment (64E-6.013(2)(a)), tanks with a double compartment: the first chamber must be 2/ 3 the total volume and the second chamber must be 1/3 of the total volume (64E-6.013(2)(a)), liquid depth must be at leas t 42 inches (64E-6.013(2)(b)), airspace must be 15% of the e ffective capacity (64E-6.013(2)(c)), the inlet device must enter one to thr ee inches above the liquid level with a diameter greater than 4 inches and must not extend greater than 33% of the liquid depth below the water surface (64E-6.013(2)(d)), the outlet device must have a diameter greater than 4 inches and extend down below the water surface between 33% to 44% of the liquid depth (64E-6.013(2)(e)), the inlet and outlet devices must be on opposite ends of the septic tank (64E6.013(2)(f)), and constructed of concrete, fiberglass, corro sion-resistant steel, or other equally durable material ((64E-6.010(2)(a)(1)). Concrete septic tanks are the most common constructed septic tanks while fiberglass septic tanks are used in areas wher e the heavy concrete septic tanks cannot be transported. Concrete septic tanks are typically rectangular in shape with a 2:1 length-towidth ratio (Canter and Knox, 1985). The widt h of a concrete sept ic tank generally

PAGE 26

13 tapers approximately two inches from the top to the bottom. The width profile is usually a taper or a V-bottom profile (Figure 2-2). Although concrete tanks are commonly used, they have difficulty remaining watertight from corrosion or at the seal of the tank and the tank lid. A fiberglass septic tank is commonly cylindrical an d easily remains watertight while in service. Sludge Scum Effluent Inlet Tee Outlet Tee Figure 2-1 A Multiple Chamber Septic Tank Schematic Figure 2-2 Septic Tank Width Prof iles (a) V-bottom (b) Taper Septic tank capacity must be adequate to allow sufficient retention of wastewater while storing the accumulated solids. The estim ated wastewater flow to an OSTDS is 50 gallons per person per day. The effective volu me of a septic tank is the volume required for twenty-four hour retention of entering wast ewater and is located between the sludge

PAGE 27

14 and scum layer (Khan et al., 2000). The effec tive capacity is the volume below the liquid in the septic tank (64E-6.002(20)). The requi red minimum effective capacity for a home is based on the regulated estimated flow of tw o occupants per bedroom (Table 2-1) and is outlined by the Florida Administrative Codes of Standards. Minimum effective septic tank capacities for different average sewa ge flow are presented in Table 2-2. Table 2-1 Residential Estimated Sewage Flow* Single and Multiple family per dwelling Estimated Sewage Flow (Gallons/Day) 1 bedroom with 750 sq. ft. 100 2 bedrooms with 751-1200 sq. ft. 200 3 bedrooms with 1201-2250 sq. ft. 300 4 bedrooms with 2251-3300 sq. ft. 400 *For each additional bedroom or each additional 750 sq. ft., the estimated sewage flow increases by 100 gallons per dwelling unit. Table 2-2 Minimum Effective Septic Tank Capacities Average Sewage Flow (Gallons/day) Mi nimum Effective Capacity (Gallons) 0 – 200 900 201 – 300 900 301 – 400 1050 401 – 500 1200 501 – 600 1350 601 – 700 1500 Septic tank operation Primary treatment of wastewater is perf ormed within the septic tank operation, consisting of separation of settable solids from wastewater, digest organic matter, store settled solids, and discharge of clarified liquid for further tr eatment and disposal in the drainfield. The septic tank separates so lids and grease from liquid through gravity settling or floatation. The wast ewater flow is reduced once it enters the tank, allowing solids to sink to the bottom while fats and grease float to the top (U.S. Department of Health, Education, Welfare, 1967). The solids that rise to the top of the liquid level

PAGE 28

15 consisting of fat and grease are termed “scum” and the solids that sink to the bottom of the tank are termed “sludge”. The effluent within the septic tank containing scum and sludge is termed septage. The scum and sludge combined represent th e total solids in the septic tank. Wastewater clarif ication is promoted by three main design parameters: tank depth, retention time, and chambers (Cante r and Knox, 1985; U.S. EPA, 1980; Barshied and El-Baroudi, 1974). A large tank depth in creases the available depth for storage and settling (Barshied a nd El-Baroudi, 1978). Retention time is the average time that th e wastewater spends in the septic tank from entry to exit and is a function of the effective volume, daily household wastewater flow, and the volume of stored solids (Kahn et al., 2000). As the sludge depth increases, the liquid volume and detention time in the se ptic tank will decrease (U.S. EPA, 1980). At maximum sludge depth, the septic tank should be able to retain the wastewater for a minimum of 24 hours (Kahn et al., 2000; U. S. EPA, 1980). However, under ordinary conditions when the storage is not at capacity, wastewater may be retained in the septic tank for up to three days (Kahn et al., 2000). Multiple chambers prevent solids from exiting the septic tank when mixing is induced by hydraulically overloading the tank. Multiple chambers also decrease mixing and increase the removal of biochemical oxygen demand (BOD) and suspended solids (U.S. EPA, 1980). The multiple chambers allo w mixing of solids with liquid in the first chamber, while the second compartment recei ves wastewater at a lowered velocity allowing the remaining solids to settle from th e wastewater again before effluent exits the tank (Canter and Knox, 1985). A tank with multip le chambers will lead to longer service time between pump outs (Canter and Knox, 1985).

PAGE 29

16 Solids storage uses the remaining septic tank volume that is not required for the effective volume to settle solids. Scum stor age is a layer at the top of the liquid level with two-thirds of the layer above the liquid and one-third of the layer submerged (U.S. EPA, 1980). Forty percent of the septic tank volume is typically designed for sludge and scum storage (U.S. EPA, 1980). Maintenance must be performed when the scum or the sludge layer is endangered of exiting the tank. Stored solids are partially degraded within the septic tank. The septic tank is an anaerobic environment, thus the term “sep tic” (U.S. EPA, 1980; Laak and Crates, 1978; U.S. Department of Health, Education, Welfare, 1967). The available anaerobic microbial cultures partially decompose and liquefy solids (U.S. EPA, 1980; Laak and Crates, 1978; U.S. Department of He alth, Education, Welfare, 1967). The microorganisms in the septic tank destroy pathogens, mineralize organic matter, and oxidize material (Canter and Knox, 1985), wh ile reducing sludge and scum to finer particles, liquid, and gas duri ng decomposition and digestion (U .S. Department of Health, Education, Welfare, 1967; Amerisep Inc., 1999) The major chemical s in the retained solids are carbon, hydrogen, nitrogen and sulfur that are transformed during digestion and decomposition to methane, carbon dioxide, water, ammonia, and hydrogen sulfide (Baumann, 1978, Wilhelm et al., 1994). Drainfield Design and Operation The drainfield treats and disposes clarified effluent by distributi ng it into the soil for percolation (U.S. Dept. of Agriculture, 1982 ). The soil type and appropriate sizing determine treatment performance of clarified effluent in the drainfield. The treatment in the drainfield is final treatment of the e ffluent before dispos al and is achieved by percolation and biol ogical degradation.

PAGE 30

17 Drainfield design The drainfield is designed to discharge cl arified effluent into the soil below for final treatment and disposal (K ahn et al., 2000). The drainfield uses either an adsorption bed or a drain trench with a mineral aggregat e for disposing clarifie d effluent to the soil (64E-6.014(5)). The drainfield size de pends on of the soil type and estimated wastewater flow (64E-6.008(5); U.S. Departme nt of Agriculture, 1982). Soil types that are slightly to moderately limitation are satis factory for standard subsurface systems that are determined by a percolation test. A limite d soil type is defined as by the percolation rate with a slightly limited soil having a perc olation of less than 2 minutes per inch and a moderately limited soil having 5 to 10 minutes per inch. Severely limited soil types have a percolation rate of greater th an 30 minutes per inch or less than one minute per inch and a water table less than 4 feet below the drai nfield and are unsatis factory for standard subsurface systems because the soil type will not promote the minimum 2 foot unsaturated soil condition needed for proper treatment (64E-6.008(5)). A drain trench is the preferred method of subsurface drainfield systems (64E6.014(b)). The trench system consists of a pe rforated pipe discharg ing clarified effluent within its own trench (Brown and Peart, 1996). The trench cannot be greater than 36 inches wide (64E-6.014(5)(a)). A trench widt h less than 12 inches must have a minimum of 12 inches separating the sidewalls of adjacent trenches (64E-6.014(5)(a)), while a trench width greater than 12 inches must have a minimum of 24 inches separating the sidewalls of adjacent trenches (64E-6.014(5)(a)). An absorption bed system must have the en tire earth content of the absorption area removed and replaced with aggregate and distribution pipes (64E-6.014(5)(b)). The perforated pipes are all in the same trench, being the single bed. The bottom surface of

PAGE 31

18 the absorption bed must not exceed 1500 s quare feet (64E-6.014(5)(b)), and the dimensions of the absorption bed must achie ve maximum length-to-width ratio practical (64E-6.014(5)(b)). The maximum depth of the drainfield from bottom to finished surface must not exceed 30 inches with a minimum earth cover of 6 inches (64E-6.014(5)(e)). A polyester bonded layer is used to preven t earth backfill from infiltra ting and is placed only on top of the drainfield (64E-6.014(5)(e); Brow n and Peart, 1996). The mineral aggregate material that is used within the trench or bed is either limestone, slag, quartz rock, granite, river gravel, recycled crushed concre te, lightweight aggregat e, or another equally durable material (64E-6.014(5)(c)1). The to tal depth of aggregate must be at least 12 inches throughout the bed or tr ench with a minimum of 6 in ches below the pipe, but not exceeding 10 inches when total depth is at the minimum (64E-6.014(5)(c)1). A profile of a drainfield is shown in Figure 2-3. Backfill Mineral aggregate Original soil Polyester bonded layer Perforated pipe 6 ” 12 ” Figure 2-3 Drainfield Profile Drainfield operation Septic tank effluent is discharged into the drainfield for further treatment through biological processes, adsorp tion, and infiltration into unde rlying soil (U.S. EPA, 2002).

PAGE 32

19 The clarified effluent is discharged from perforated pipes through aggregate to evenly distribute effluent to the soil. Remaining so lids (suspended) in the effluent will form a clogging mat above the soil layer, lowering hydraulic conductivity that prevents soil saturation (Ayres Associates 1993; U.S. EPA, 1980). The clarified effluent receives primary treatment as it percolates through the so il and is disposed of to the water table. During percolation, clarified effluent is treated by physically entrapping the remaining particulate matter in the clarified effl uent and is responsible for the majority of wastewater treatment (U.S. EPA, 1980). The clarified effluent percolates through unsaturated soil to provide adequate re moval of pathogenic organisms and other pollutants from the effluent before reachi ng the groundwater (Bicki, 1989; U.S. EPA, 1980). The drainfield is res ponsible for treating organics, inorganics, and pathogens in the clarified wastewater. Af fective treatment is accomplished by a complex arrangement of primary minerals and organic particles that differ in composition, size, shape, and arrangement in the so il (U.S. EPA, 1980). The quality of wastewater treatment depe nds on how the effluent moves into and through the soil. Treatment in the soil depends on the soil’s physical properties: size, shape, and continuity of pore space (U.S. EPA, 1980) and is dependent on the wastewater nature, soil type, and degree of saturation (Brown, 1998). Unsaturated soil forces clarified effluent to flow through smalle r pores, maximizing treatment compared to saturated soil where smaller pores are occupi ed by water (U.S. EPA, 1980). The clarified effluent travels more slowly in unsaturated so il than in the same soil when saturated. The slower the velocity of flow, the longer th e residence time of th e wastewater in the

PAGE 33

20 unsaturated soil and the greater the opportunity to treat th e wastewater as it travels through the soil (Brown, 1998). The two most important soil attributes are soil permeability and seasonal high ground water table (Brown, 1998). Soil permeabili ty refers to the ab ility of a soil to transmit water or air (U.S. Department of Agriculture, 1984). Permeability is based on the soil characteristics observed in the field, particularly structure, porosity, and texture (U.S. Department of Agriculture, 1984). Low permeability, such as in clayey soils, would prohibit vertical flow and would re sult in horizontal flow with little or no treatment. A high permeability soil, such as sa ndy soil, has rapid ver tical flow with little residence time in the unsaturated soil, resulting in limited treatment. Final disposal occurs when the treated clarified effl uent has percolated through the unsaturated soil and reaches the water ta ble. In areas limited in unsaturated soil depth, the soil must be built up (mounded) to meet this requirement. Once the effluent makes it to the water table, its concentration will dilute and eventually make its way to surface water or a lower aquifer. OSTDS Maintenance Inspection ensures that the system is func tioning as designed. Pumping the septic tank should be done when accumulated solids have reached the storage capacity. A combination of visual, physical, bacteriologi cal, chemical, and remote monitoring can be used to access system performance (U.S. EPA, 2002). A recurring weakness of many existing OSTDS management programs has been the failure to ensure proper operation and maintenance of installed systems (U.S. EPA, 2002).

PAGE 34

21 Annual Inspection The type of inspection and frequency shoul d be determined by the size of the area, site conditions, resource sensitivity, the comple xity of the system, and number of systems (U.S. EPA, 2002). Mandatory in spections are an effective method for identifying system failures or systems in need of corrective ac tion (U.S. EPA, 2002). The inspection would ensure the system is functioning properly a nd identify any obvious problems such as the septic tank structure and accumulated solid s level (Crites and Tchobanoglous, 1998; U.S. Department of Health, Education, Welfare, 1967). Scheduled inspections during seasonal rises in ground water levels facilitate monitoring of performance during “worst case” conditions (U.S. EPA, 2002). The OSTDS should be inspected for the following: 1. watertight tank condition, 2. clogs in the entrance and exit baffles, and 3. accumulated sludge and scum levels. Maintenance Pumping Tank pumping or other routine maintenan ce tasks are seldom required or even tracked by regulatory authorities of manage ment for information purposes (U.S. EPA, 2002). Septic tanks must be pumped when solid layers are above designed storage capacity to prevent solids from entering the dr ainfield and ensure proper operation (U.S. EPA, 1980; U.S. Department of Health, E ducation, Welfare, 1967). The septic tank reaches capacity when the retention time is less than twenty-four hours or the sludge layer is within three inches of the bottom of the exit baffle (U.S. EPA, 1999; U.S. EPA 1980; U.S. Department of Health, Education, Welfare, 1967). The pumping frequency is dependent on the accumulation rate of solids that vary from system to system and is a factor of septic tank design, wastew ater characteristics, and drainfield performance (U.S. EP A, 2000b; Vogel and Rupp, 1999; Bounds, 1996;

PAGE 35

22 Mancl, 1984). Recommended pumping freque ncies range from 2 to 12 years (Benton County Environmental Health, 1998; Jones and Yahner, 1992; Loudon, 2002). In some counties such as Brown County, WI, the pumpi ng frequency is regulated. In this particular case, tanks are re quired to be pumped out every three years unless the solids are less than one-third of liquid capacity (County Code s 11.073(c)(5)(a)). Pumping a system too often increases the volume of se ptage that must be unnecessarily treated. EPA Management Guidelines The importance of OSTDS management became a national issue when it was found that improperly operated systems were beco ming contributors to major water quality problems. The U.S. EPA created OSTDS Management Guidelines to raise the level of performance of OSTDSs through improved management programs (U.S. EPA, 2000). The management guidelines present five se parate model programs as a progressive series where management requirements become more rigorous as the system technologies become more complex or when environmen tal sensitivity increases. The management guidelines are voluntary and apply to all OSTD Ss. The models are structured to allow communities to pick and choose or adopt comple te sets of manageme nt criteria that will provide the necessary level of protection while balancing co sts and other institutional factors. The model programs provided by th e U.S. EPA are intended to be benchmarks that aid communities in identifying a mana gement objective, in evaluating whether current programs are adequate, and ultimately, in determining an appropriate management program and the necessary progr am enhancements to achieve management objectives and public health and environmental goals.

PAGE 36

23 Previous Solids Accumulation Rate Research Discussion of Prior Studies Three previous studies examined solids generation in a septic tank. A study by the Public Health Service (1949) was the first ex tensive study, and the resu lts reported in this study are still consulted today (Bounds, 1992) A second study by Terry Bounds in 1986 was used to validate the results of the Public Health Service. A third study by J. D. Moores in Novia Scotia was performed in 2002 to examine accumulation rates in OSTDSs. United States Public Health Service The United States Public Health Se rvice (USPHS) presented a study on the accumulation rate of solids in a septic tank in 1949. The USPHS study used 300 single family homes with septic systems in 9 areas Dallas, TX; Kansas City, MO; Cook County, IL; St. Joseph, IN; Cincinnati, OH; Kalamazoo, MI; Warwick County, VA; Cuyahoga County, OR; Montgomery County, AL; and Dade County, FL. An inspection was made of each home that had available history on its system. The criteria for participation was that it 1. must be a single family home, 2. have reasonably accurate history with known last pump out date of the tank, 3. the tank could not be full, and 4. the outlet device must be intact. The inspection documented the number of people occupying the home, the number of bedrooms, water usage from the water mete r, the discharge units (bathroom, laundry, kitchen and/or water closet), and the measured solids in the septic tank. A total of 205 tanks were used in thei r analysis, with years of service ranging from 0.5 to 39 years (Table 2-3). The years of service is the time since either the tank

PAGE 37

24 was pumped-out or installed. The mean a nd median accumulation rates in gallons per person per year for the particip ants who had their systems in service for 2 years or less are provided in Table 2-4. Table 2-4 shows that the accumulation rate in these tanks was high in the first half year of service, after which it quickly decreased. Table 2-3 USPHS Septic Tank Years of Service (Weibel et al., 1949) Years of Service Number of Participants 0.5 4 0.75 4 1 13 1.5 2 2 13 3 24 4 14 5 14 6 30 7 18 8 23 9 19 10 4 11 6 12 5 13 4 16 1 20 3 21 1 32 2 39 1 Table 2-4 USPHS Accumulation Means and Medians (Weibel et al., 1949) Years of Service Number of Reports Mean Scum Mean Sludge Mean SC* & SL* Median Scum Median Sludge Median SC* & SL* 0.5 4 17.35 71.44 88.79 19.60 63.06 89.61 0.75 4 2.84 31.34 31.94 0 32.39 34.41 1 13 5.16 18.25 23.41 2.02 16.23 22.59 1.5 2 13.09 8.53 21.62 13.09 8.53 21.62 2 24 4.04 10.17 14.21 2.84 9.35 15.41 SC = scum; SL = sludge.

PAGE 38

25 From the results of the Weibel et al. study, the USPHS concluded that sludge and scum accumulated more quickly per person in the first 6 years of operation. Sludge accumulation became constant at the 7-year point, while scum accumulation became constant at the 3-year point. Septic tanks with capacities less than 125 – 175 gallons per person retained fewer solids than tanks greater than 175 gallons per person. The lower capacity tanks could result in a lower retention than the larger was because of a lower retention time that allowed settling of the solids. The increased depth of the liquid level was found to increase the solid removal from the wastew ater that also increases retention time, increasing solids accumulation. The averag e accumulation of scum, sludge, and total solids is presented in Figure 23 with values in Table 2-5. 0 5 10 15 20 25 30 35 0510152025Years of ServiceSolids Accumulation Gallons/person/yearSludge & Scum Sludge Scum Figure 2-3 PHS Rate of Scum & Sludge Accumulation. The points marked on the figure are from the mean accumulation rate of each year and the trend line marks the average accumulation over al l. (Weibel et al., 1949)

PAGE 39

26 Table 2-5 Total per Capita Sludge and Sc um Accumulation (Weibel et al., 1949) Gallons/ Capita/Year Total Gallons/Capita No. Years Scum SludgeScum & Sludge Scum Sludge Scum & Sludge 1 6.21 18.33 24.54 6.21 18.33 24.54 2 3.52 12.19 15.71 9.72 30.52 40.25 3 3.22 9.58 12.79 12.9440.10 53.04 4 3.22 8.15 11.37 16.1648.25 64.41 5 3.22 7.48 10.70 19.3755.73 75.10 6 3.22 7.11 10.32 22.5962.84 85.43 7 3.22 6.88 10.10 25.8169.72 95.53 8 3.22 6.88 10.10 29.0276.60 105.62 9 3.22 6.88 10.10 32.2483.48 115.72 10 3.22 6.88 10.10 35.4690.36 125.82 11 3.22 6.88 10.10 38.6797.25 135.92 12 3.14 6.88 10.02 41.82104.13145.94 13 3.14 6.88 10.02 44.96111.01155.97 14 3.14 6.88 10.02 48.10117.89165.99 15 3.14 6.88 10.02 51.24124.78176.02 16 3.14 6.88 10.02 54.38131.66186.04 17 3.14 6.88 10.02 57.53138.54196.06 18 3.14 6.88 10.02 60.67145.42206.09 19 3.14 6.88 10.02 63.81152.30216.11 20 3.14 6.88 10.02 66.95159.19226.14 Bounds Study The Bounds study (1992, 1996) was centered in Glide County, Oregon where the largest septic tank effluent pump (STEP) syst em (in the nation) was in place. A STEP system uses septic tanks (for initial wastew ater treatment) in conjunction with a sewer system (receives clarified effluent from the se ptic tanks). A pump is in place in the septic tank that pumps the clarified effluent into the sewer lines. The use of a STEP system within a septic tank can cause turbulence and washout of solids. The STEP system in Glide County had 468 septic tanks and over 20 miles of collect ion lines. A step system, like OSTDS systems, still needs to be pumped out as solids fill the tank, and the septic tanks in Glide County were pumped when sludge was within 6 inches and scum was within 3 inches of the outlet (Bounds, 1992).

PAGE 40

27 In his study, Bounds used 450 tanks in G lide County. Residents were interviewed and information on the number of people, thei r ages, and their habits that would impact performance was gathered (Wilcox, 1992). A tota l of three measurements were taken in this study at 2.8 years, 5 years, and 8 year s. The first measurement of solids was 2.8 years after initial pump out, and 19 of the tanks were randomly selected for solids measurement 5 years after pump out. On th e third measurement at 8 years after pump out, solids were measured in all the tanks again. Figure 2-4 illustrates the average accumulation of total solids in Glide County. 0 20 40 60 80 100 120 0246810Time (Years)Total Solids Volume per Capita (Gallons) Figure 2-4 Bounds Study Volume of Total Solids For Eight Years As shown in Figure 2-4, after 8 years, the so lids levels were at half of the storage capacity. Bounds (1992) also no ted that microorganisms requi red up to 2 years to reach solid decomposition activity levels that ar e high enough to impact accumulation rates. The results of this study also showed that th e infiltration of groundwater resulted in solids accumulation decreasing and that scum accumu lation increased with increased garbage disposal use. The Bounds Study is the first and only study that observed the

PAGE 41

28 accumulation of solids over an extended period of time, unlike the single inspection made by the Public Health Service study. Moore Study The Moore study (2002) centered in Nova Sco tia and presented a literature review and results of a field analysis of pumpi ng frequencies and maintenance procedures. Measurements were collected from 40 tanks that had accurate records of the most recent pump out. The OSTDSs used in this st udy, ranged in operation time from 0.75 to 12 years from the last pumping and ranged in the occupants it served from 1 to 60 occupants. The mean and median numbers of year s of service were 3.64 years and 3 years, respectively, whereas the mean and median occupants in the home were 6.4 people and 3 people, respectively The average sludge accumulation rate from those tanks was 10.93 gallons per person per year, and the scum accumulation rate was 5.86 gallons per person per year. Table 2-6 Moore Study (2002) Distri bution of Years of Service Years of Service Number of Systems 0.75 1 1 3 1.5 3 2 3 2.5 2 3 11 4 6 4.5 1 5 6 6 2 11 1 12 1

PAGE 42

29 Table 2-7 Moore Study (2002) Scum and Sludge Accumulation Trends Years of Service Number of Reports Mean Scum Mean Sludge Mean SC* & SL* Median Scum Median Sludge Median SC* & SL* 0.75 1 20.36 0 20.36 20.36 0 20.36 1 3 12.09 0.85 12.94 9.16 0 9.16 1.5 3 17.41 7.54 24.94 16.07 9.04 28.12 2 3 17.73 6.53 24.26 22.91 3.05 17.82 *SC = Scum; SL = Sludge. The results of this study in Novia Scotia were used to educate homeowners in best management practices. While Moore did not determine significant influences on accumulation, he but did discuss the effects of sy stem additives and water softener brine. System tank additives, in some cases, result ed in limitations in solid separation from wastewater, and systems receiving water soft ener brine showed a decrease in scum accumulation. Comparison of Pump Out Frequencies The prior studies illustrate the curren t documented knowledge in the accumulation rate of solids in the septic tank. A summary of their results is presented in Table 2-8, which lists the number of participants, the accumulation of scum and sludge in gallons per capita for the first year, the model e quation for total solids, and the solids measurement method. The accumulations in th e first year for the PHS study (1949) and the Moore study (2002) are similar. Also, the Bounds study (1992) is considered to be in agreement with the PHS study in terms of accumulation rates, even though the 1-year sludge and scum accumulation volumes are not available.

PAGE 43

30 Table 2-8 Summaries of Prior Studies Study Participant Count 1 year Sludge Accumulation Gallons/Capita 1 year Scum Accumulation Gallons/Capita Total Solids Model* Gallons/Capita Method of Measurement PHS, 1949 205 18.33 6.21 8.6t + 14.96 Single Inspection Bound, 1992 450 N/A N/A 23.4t0.7 Multiple inspections during 8 years Moore, 2002 40 16.94 5.91 22.85t Single Inspection t = time, years. The volume of total solids accumulated during the first year is within less than 25 gallons per capita for all 3 studies. Th e PHS and Bounds studies result that the accumulation rate during the first year is greater than the accumulation rate in subsequent years. The PHS and Bounds studies also us ed over 200 participants, with the Bounds study using twice the number of participants than with the PHS study. Unlike the PHS and Bounds study, the Moore study had less than 50 participants and had a constant accumulation rate from the first to the last year (8th). The shortcomings of these studies were th e lack of statistical information and the method of measurement. Unfortunately, th e studies did not present the standard deviations for the data that was collected. The standard deviation was calculated for the Moore study with the mean and standard de viation for scum, 23.32 gallons per year and 28.74 gallons per year, respectively, and fo r sludge, 40.46 gallons per year and 47.78 gallons per year, respectively. The singl e inspection made during the PHS and Moore studies assumed that accumulation trends in the OSTDSs are similar. More than one measurement from a system determines accumula tion trends that result in identifying the accumulation rate peak for each solid. In the Bounds study two measurements were

PAGE 44

31 made, and the peak volume is assumed to be between 2.8 years and 8 years. The Bounds study was the first to monitor an OSTDS ove r an extended time period after pump out. The objective of this study was to determine the accumulation rate for scum and sludge during the first year of service. The accumulation rate was determined from multiple measurements of over 200 participants Performance variab les were determined from wastewater, system design, and surroundi ng environmental ch aracteristics that could possibly affect the accumulation and those variables that do affect the system were to be included in a model to predict solid s accumulation. The overall outcome of this study is an attempt to produce best manageme nt practices to control solids accumulation, along with the expected solids accumulation rate when consid ering an individual system in its entirety.

PAGE 45

32 CHAPTER 3 METHODS Objectives The objectives of this study were to identif y the relevant variables, collecting them from a select population, devel op a model with the collected data and assess the relative impact of variables to the OSTD S performance. The result of this study is aimed to also develop best management prac tices that homeowners can implement. The goals used to address these objectives was: Identify potential performance variables fr om household activity, system factors, and surrounding environment characteristics, Create a survey to collect identified pe rformance variables from OSTDS-using homeowners, Create a database of the systems to store contact information, collected performance variables, a nd inspection measurements, Determine expected accumulation rates for scum and sludge, Determine what performance factors th at impact OSTDS performance, and Create a model using performance fact ors that impact OSTDS performance. In this study, the OSTDS performance a nd management practices were monitored over a sample population of 221 Charlotte C ounty residents to determine the most significant underlying factors that influence accumulation of solids. Potential performance-influencing variables were identified and databased by UF using a combination of surveys, permits, and inspec tions. After pumping out the participating homeowners’ OSTDS during an initial inspec tion by CCDOH, the depths of solids were measured at approximately 6and 12-mont h time intervals, and this accumulation information, transferred to UF, served as the response variable in multiple linear

PAGE 46

33 regression (MLR) models. The Biostatistics Co nsulting Laboratory in the Department of Statistics at UF performed a ll analysis, and the resulting tr ends showing which variables influenced solids accumulation were identified. Task 1: Identification of Relevant Variables As a first step in better understanding th e problem of OSTDS failure and its causes, all factors influencing accumulation were de termined using an exhaustive literature search of OSTDS care and maintenance fact sh eets, reports from previous research, and manuals for system management. The factor s identified in the literature as having potential impact on OSTDS performance were categorized into three major groupings describing 1) wastewater characteristics, 2) system design and condition, and 3) surrounding environment. The wastewater characteristics, consisting of hydraulic loading and wastewater quality, are factors that describe the wastewater that enters into the system from the home. The OSTDS system design and condition c onsists of specific information on the septic tank and the drainf ield. The surrounding environment consists of the site elevation and groundwater elevation. A more thorough description of each grouping of factors is provided below. Wastewater Characteristics The hydraulic loading and quality of wa stewater entering the system from the home can be best predicted by household prac tices, such as occupancy, home activity, home characteristics, and water cons umption (U.S. EPA, 2000; Crites and Tchobanogloos, 1998; Anderson and Siegrist, 1989; Siegrist, 1983). Home activity varies with occupants’ pr actices and includes water-usi ng appliances and disposal practices (U.S. EPA, 2002; U.S. EPA, 2000a). Home description f actors typically stay constant despite change in occupancy and include water-conservi ng plumbing fixtures,

PAGE 47

34 water-using appliances, water source, a nd home characteristics (U.S. EPA, 2002; Hammer and Hammer, 2001; Kahn et al., 2000). Occupancy factors po tentially impact water characteristics by the number and age of residents, annual time of occupancy, and ownership period. The number of residents significantly alters water consumption and wa stewater production (U.S. EPA, 2000). The annual occupancy duration differentiates seasona l residences that accumulate solids for a short period from year-round residences, which ac cumulate solids all year. The seasonal residences allow the system to rest, resu lting in less accumulation; however, a longer length of residency result in a more acc limated microbial system for decomposing organic particles, thus decr easing accumulation as well. Water-using appliances and homeowner pr actices alter the hydraulic loading and wastewater quality. Wastewat er-creating appliances are typically washing machines, automatic dishwashers, and garbage disposals, which drain to the septic tank (Kuhner et al., 1979). Washing machine and dishwasher descriptions alter the hydraulic loading depending on load capacity and number of loads per week. Water-conserving washing machines, typically front-loading, use significantly less water compared to traditional top-loading machines. Deterg ent type and use, liquid fabr ic softener, and bleach also alter wastewater quality. Kitchen sink activity influences wastewater For example, removal of solids from dishes to a solid waste container before cl eaning in a sink or dishwasher reduces the amount of particles exiting through the drain (K uhner et al., 1979). Ga rbage disposal use, therefore, increases solid accumulation by in troducing food particle s into the system (U.S. EPA, 2002; Hammer and Hammer, 2001; Bounds, 1996). Also, frying foods

PAGE 48

35 compared to baking introduces a higher amount of oil and fats if the grease from frying is disposed down the sink drain (U.S EPA, 2002; Kahn et al., 2000). Direct disposal of solids other than to ilet tissue and non-water liquids increases solids accumulation. Typical liquids other th an water that are disposed in the drain include paint thinners, pesticides, salad dressi ng oil, sour milk, disi nfectants, bleach, and food grease. Typical solids that are imprope rly introduced in the wastewater system are feminine products, disposable diapers, plas tic items, nylon products, medications, rubber products, cigarette filters, paper towels, a nd any type of food item (U.S. EPA, 2002; Hammer and Hammer, 2001; Lesikar, 1999a). System Design System design components are functions of the septic tank and drainfield (Lesikar, 1999b; Laak, 1980). The septic tank’s age, dimensions, tank volume, number of chambers, and number of tanks along with the drainfield configuration, area, and elevation are included in this study. Syst em age is used to note an impact of performance, especially with the many sy stems in the nation over 30 years old. The drainfield description is used to determine if the drainfield impairs or promotes the performance of solid accumulation. When a drainfield is not ope rating correctly and drainage is not occurring, water can reenter in to the septic tank allowing solids to exit. Bounds (1996) noticed this effect from hi gh groundwater levels on accumulation in the septic tank. The elevation of th e drainfield is in relation to the elevation of the center of the paved frontage road of the residence. Surrounding Environment The surrounding environment factors that potentially hinder system performance are site elevation and the contact surface of the tank or drainfields with the groundwater.

PAGE 49

36 The elevation of a system determines its ab ility to drain and the possibility of water infiltration. Systems in contact with groundw ater can cause infiltration in leaky tanks (Bounds, 1996), while storm and floodwaters that flood drainfields can cause infiltration to both leaky and non-leaky tanks. The estimated water table is the water level that is expected to be in a year of normal rainfa ll during the wet season characterized by zero pore pressure or simply described as the wate r level in an unlined, augered hole at the end of the wet season in a year of normal rainfall. As previously mentioned, the purpose of the literature review phase of this project was to construct a thorough list of all potential factor s that may impact OSTDS performance. The potential performance vari ables that were included on this list are presented in the results chapter to follow Values of each these variables were subsequently obtained by a combination of su rveys of selected participants, permits, and inspections. Task 2: Selection and Recruitment of Participants Three criteria were used in c hoosing participants. First, a participant should live in a region with dominant soil type containing 2% or more of the total population of OSTDSs in Charlotte County. Using system s within these “most populated” soils would ensure representation of a majority of Ch arlotte County’s OSTDS population. However, because of the unanticipated difficulty th at CCDOH would have in visiting the large number of widely distributed OSTDSs, a sec ond criterion was followed that participants would live in only one largely populated regi on of Charlotte County in proximity to CCDOH. Finally, the third crit erion was the willingness of the selected residents to participate in this study. Below is a detail ed description of how participants were randomly selected and recruited to participate in this study.

PAGE 50

37 Subtask 2A: Participant Selection Location of systems in Charlotte County The Charlotte County GIS (CCGIS) Department located homes with OSTDSs from sewer line data and property parcel info rmation obtained from the Charlotte County Property Appraisers. The propert y parcel information and the sewer line data were then transferred to a map of the region to identify which homes have sewer services or OSTDSs. Properties that were in contact or adjacent to the sewer lines were considered sewer-using properties. The remaining propert ies were then identified as OSTDS-using properties. Identification of OSTDS density by soil type A map showing which residences possesse d OSTDSs was subsequently overlayed with soil types in Charlotte County using ARC GIS software (ESRI, Redlands, CA, USA). The resulting map, Figure 3-1, allowe d counting of the number of OSTDSs in each soil type and, ultimately, the determina tion of which soil types contained the most systems. Random selection of potential participants In response to a request by CCDOH, one specific area of Charlotte County was chosen for the study to ease accessibility for pump-outs and solid measurements. This region, Mid-County 2 (MC2), was selected fo r its proximity to CCDOH and high density of OSTDSs (refer to Figure 3-1). Forty-five percent of the county’s systems (and nearly 50% (20,822) of the systems when consideri ng “most populated” soils only) are in MC2. The CCGIS Department randomly extracted 2,300 systems from their database using ARC GIS utilities. The property identification number was cross-referenced with the property appraiser’s database to extract the owner’s name and mailing and physical

PAGE 51

38 addresses, and this information was transfe rred to a master Acce ss (Microsoft, Mountain View, CA, USA) database. Subtask 2B: Recruiting of Participants Recruitment efforts began in October 2001 and ended in June 2002 using a combination of methods as described below. Newspaper article In March of 1999, the Charlotte Sun Herald published an article announcing the pilot program that will involve 400 OSTDS users. The article provided contact information for interested homeowners. Also, residents were informed of a free septic tank pump out for their participation. Mailing campaign The mailing campaign was focused on resi dents with OSTDSs selected by the CCGIS Department. The volunteers who res ponded to the newspaper article were also included in the mailing campaign. The maili ngs consisted of a postcard followed by a delivered package one week later. The postc ard informed the residents of the study and that they would soon be receiving a packag e within the following week. The packages consisted of the following items: 1. a flier describing what was requested of the participants and how the gathered information would be used (Appendix A), 2. two consent forms: one for the resident ’s record and one to sign and mail back (Appendix A), 3. the initial survey (to be discussed below), 4. a self-addressed and stam ped return envelope, and 5. a pamphlet on system care.

PAGE 52

39 Figure 3-1 Selected Systems in Mid-County 2 Basin per Soil Type

PAGE 53

40 A followup postcard was mailed a month after the survey to remind those participants not responding to the mailings to do so as soon as possible. Five mailings totaling 1,512 packages were mailed from Oc tober 2001 to May 2002 in order to recruit participants. County fair A booth at the Charlotte County Fair was used for recruiting from February 15-23, 2002. CCDOH and UF staff manned the fair booth and provided educational information on system operation and maintenance and was used to invite residents to participate in the study. Residents who volunteered to participate completed the consent form and initial survey at the booth and received a pamphlet flier, and a copy of the consent form. Although the mass mailings and newspapers were distributed to many, the results were relatively poor for part icipant recruiting. The fair booth was the best method for recruiting participants, most likely because most people feel more comfortable receiving information in a personal conversation wher e they can have their questions answered with an immediate response rather than from passive sources, such as the fliers mailed and articles printed in the newspaper that pl aced the burden on them to call for additional information. Subtask 2C: Division of Recruits into Phase 1 and Phase 2 of the Study The list of participants in the study was divided into two phases, and, in doing so, care was taken to make certain that Phase 1 and Phase 2 contain an even distribution of the studied performance (independ ent) variables. The groupings of the participants were randomly prepared taking into account only information received in the initial survey of household characteristics. To ensure even di stribution of characteristics, both qualitative data denoted by “yes” or “no” (e.g., washi ng machine draining to septic tank) and

PAGE 54

41 quantitative data (e.g., number of people per home) were divided. The quantitative data were first converted to two levels, high (H ) and low (L), depending where they fell in relation to a median value. The resulting percent distributi on of high and low levels of each was maintained for both Phases 1 and 2. These results will be discussed in Chapter 4. The pump out date was also used to separa te the phases so that participants whose systems were the first to be pumped would be in Phase 1, while those whose systems pumped last would be in Phase 2. The pump out date ensured that Phase 1 final measurements would be completed in a timel y manner for subsequent analysis. There were 179 Phase 1 participants a nd 42 Phase 2 participants. Subtask 2D: Data Collection and Databasing As previously described, the independent variables for the constructed model are the performance variables that have potential to significantly impact system performance, represented in this study as accumulation rates. The performance variables were collected by means of surveys, permits, and in spections. Survey information was mostly completed by mail, but could have been completed in person or by telephone. Initial survey With consultation with Dr. Chris McCarty of the UF Survey Research Center in the Bureau of Economic and Business Research an d reference to previous CCDOH surveys, special consideration was taken in the design of the initial surv ey in order to enable each OSTDS owner to accurately provide as many of the potential perfor mance variables for each system as possible. As previously de scribed, the initial surveys were sent to prospective participants in Charlotte County from Dece mber 2001 to June 2002 after receiving approval from the UF Institutional Review Board (IRB). The initial survey,

PAGE 55

42 shown in Appendix B, allowed collection of information on residency, home activity, home description, and surrounding environment. Follow-up survey A followup survey, also approved by UF’s IRB, was sent to the participants to clarify answers to questions that were asked in the initial survey, to ask more detailed questions, and to note any changes in habit. Most participants mailed their surveys back, while others were called to complete the su rvey by phone. The followup survey was sent to participants within 6 months to one year after they had received the initial survey, and a copy of the followup survey is provided in Appendix B. Permit information Permits of most of the participants’ OSTDSs were obtained from CCDOH, and information concerning system descripti on and characteristic s of the surrounding environment was gleaned from these documents and transferred to the Access database. It is important to note that, of the 221 participants, 25 permits could not be located. As a result, the system and environmental data were either left blank or estimated. Inspection information Initial inspections of each participan t’s OSTDS were performed by CCDOH as a means of judging eligibility for participation in the project. Their criteria for eligibility was that the system could not be experienci ng a failure, must operate properly, and have an intact outlet-tee. While at each home, CCDOH was also able to collect valuable information for the modeling phase, in cluding the corrosion condition and water consumption. Also during the initial inspec tion, the septic tank wa s pumped out, the tank condition evaluated, and water use determined.

PAGE 56

43 Height measurements After the initial inspection, two measurement inspections were performed at 6 and 12 months to obtain the change in height of scum, sludge, and liquid in the tank. The CCDOH personnel used a raven meter to measur e sludge height and a measuring tape to measure the height of scum. A raven meter is a device that uses light to detect solids. When light is blocked by solid particles in the tank, it is assumed that the sludge blanket begins at that elevation. The scum is not uniformly thick in th e tank, and the average thickness must be estimated. Measurements we re taken at the exit end of the tank, unless the septic tank was a multiple chamber tank where measurements were taken in the first chamber. Databasing of all variables collected An Access database was created to contain the data collected for each participant. The database was first created to include the 2,300 OSTDS homes randomly selected by the CCGIS Department. Mailing labels were created from the database for recruitment from those 2,300 OSTDS homes. Separate fo rms in Access were created for entering data from the initial and the followup surveys for ease and efficiency. Task 3: Calculation of Solids Accumulation A primary focus of this project was asse ssment of the relative significance of the collected performance variab les (independent variable s) on the measured solids accumulation (dependent variables). Before regression analysis could be performed, the data needed to be converted to the proper fo rmat. The description below provides details of how the solid height data were used to calculate 6and 12-month accumulation rates. In order to begin creating a model, it was necessary to translate a change in sludge and scum heights to a volume change. With these volume changes in hand, an

PAGE 57

44 accumulation rate of sludge and scum was determined. A discussion of how these volume rates were calculated follows. Subtask 3A: Determination of Tank Dimensions The tank volume and manufacturer for each participant was collected from permit information. Tank schematics were collected from the CCDOH and Mr. Paul Booher of the Florida Department of Health located in Gainesville, Flor ida. A total of 10 different manufacturers’ tanks were pr esent in the study; however, only 8 of the manufacturers’ tank schematics, giving dimensions, were locate d. Twenty-seven participants either had no tank information or had unavailable schema tics, making it necessary to estimate tank dimensions. Two methods were used to estimate dimensions depending on the tank volume. Figures 3-2 and 3-3 illustrate the dimensions of V-bottom and taper-side tanks (respectively) with the appropriate nomenclature. The taper-side tank maintains a constant sidewall slope from the inlet to the bottom of the tank, unlike the V-bottom tank that has 2 different sidewall slopes with the slope being greater at h3 than at h2. Those tanks with no available dimensions and less than 600 total gallons volume (representing 2.3% of the 221 OSTDSs in this study) were assumed to have a 2:1 lengthto-width ratio, a 2-inch tape r to the bottom, and a 15% airspace volume. The tank’s average surface area was calculated from the tank’s volume divided by the liquid height. The method used to calculate the tank di mensions shown in Figure 3-2 and 3-3 is provided in Appendix D. Those tanks with no available dimensions (22 systems total) and volumes of 750, 900, and 1050 gallons were assumed to have th e same average dimension ratios as the same size tanks of known dimensions. The heig ht from the entrance baffle to the lid and the outer wall width were estimated and assumed constant for each corresponding tank

PAGE 58

45 volume. The estimated dimensions were calculated using lid wi dth and length, liquid height, along with the dimension relations hips for each tank volume. The following dimension relationships noted in Fi gures 3-2 and 3-3 were calculated: w1 w2 w3 l1 l2 l3 h2 h3 h1 HL a. b. Figure 3-2 V-bottom Septic Tank Schematic with Dimensions (a) width profile (b) length profile (w1 is the width at th e top of the tank; w2 is the width at the top of the sharp bottom taper; w3 is the width at the bottom of the tank; l1 is the length at the top of the tank; l2 is the length at the top of the sharp bottom taper; l3 is the length at the bottom of the tank; h1 is the height from the top of the tank to the liquid level, h2 is the height from the liquid level to the top of the sharp bottom taper; h3 is the height from th e top of the sharp bottom taper to the bottom of the tank) h2 + h3 w1 w3 l1 l3 h1 HL a. b. Figure 3-3 Taper-Side Septic Tank Schematic with Dimensions (a) width profile (b) length profile (w1 is the width at th e top of the tank; w3 is the width at the bottom of the tank; l1 is the length at th e top of the tank; l3 is the length at the bottom of the tank; h1 is the height from the top of the tank to the liquid level, h2+h3 is the height from liquid le vel to the bottom of the tank)

PAGE 59

46 1. R1 = w2/w3 2. R2 = h2/h3 3. R3 = (w2-w1)/(h1+h2) 4. R4 = (l3-l1)/(h1+h2+h3) 5. h1 6. t (thickness of wall) The dimension parameters, w1, w2, and w3, represent the inner width dimensions, w1 at the top of the tank, w2 in the middle, and w3 at the bottom of the tank. As noted in Figure 3-4, the w2 inner width dimension was chosen at the change in slope for V-bottom profiles, and at a set distance from the bottom in taper profiles. This established distance used in taper profile tanks was 10 inches. The inner depth was also presented at these distances, defined as l1, l2, and l3, and l2 being the length in the ta nk at the break in slope like w2. The height dimension parameter is base d on the inlet baffle. The distance from the top of the tank to the center of the inlet baffle is termed h1. The distance from the center of the inlet baffle to the break where l2 and w2 is measured is termed h2. The distance from the bottom of the tank to the break where h2 ends is termed h3. Subtask 3B: Calculation of So lids Volumes in Each Tank Solids accumulation was calculated using height measurements obtained during measurement inspections. Scum and sludge heights in each part icipant’s tank were measured by CCDOH in inches and converted by UF to a volume in gallons based on tank dimensions.

PAGE 60

47 w1 w2 w3 l1 l2 l3 hsl h2 h3 h1 hsc HL Figure 3-4 Height Dimensi ons for Liquid Height (HL), Scum Height (hsc), and Sludge Height (hsl) The analytical solutions to calculate solid s volumes in a V-bottom septic tank and a taper-side septic tank are give n in Equations 3-1 and 3-2. The dimensions used in the analytical solutions are illustrated in Figur e 3-4, which also demons trates liquid height (HL), sludge height (hsl), and scum thickness (hsc). All dimensions and solid and liquid heights arepresented in units of inches, and the resulting volume is in units of gallons. (EQN 3-1) if hsl < h3 use 231 / 2 2 43 3 2 3 3 3 2 3 s s s SLh h l l l h h w w w h V and if hsl > h3 231 / 2 2 4 43 1 2 2 1 2 3 2 1 2 1 2 3 2 3 2 3 3 h h h h l l l h h h h w w w h h l l w w h Vs s s SL (EQN 3-2) 231 / *3 2 1 3 1 1 3 2 1 3 1 1 h h h w w H w h h h l l H l h VL L sc sc

PAGE 61

48 The sludge calculation in the tapered-side tanks was based on the trapezoidal width profile. Sludge heights less than h3 were calculated with the t op of the sludge blanket as the top of the trapezoid and the bottom of th e tank, and the trapezoid area is multiplied by the average length of the tank between the t op and bottom of the tr apezoid. For sludge depths greater than the h3, the volume is calculated by adding the volume of the lower trapezoid (top and bottom of h3), and the volume of the trapezoid between the top of h3 to the top of the sludge blanket. The scum volume was calculated by the scum thickness multiplied by the width and length of the tank at the liquid height (HL). Subtask 3C: Calculation of Accumulation Rates Two different methods were used to determine solids accumulation rates. An accumulation rate was calculated for the firs t six months and second six months (using the change in volume over time) while anot her accumulation rate was determined using all three data points (0-, 6, and 12-month solids volumes) us ing the least squares method. Accumulation rates were calculated on a per system basis and a per person basis. Subtask 3D: Assessment of Trends in Accumulation The accumulation of solids during the first ye ar of service was evaluated for trends, by plotting the volume of solids from the time the septic tank was pumped. The accumulation trends were assessed for a decrease, no change, or increased change in volume from 6 months to 12 months and grouped accordingly. The accumulations that increased were grouped by comparing if the change in volume during the first 6 months was equal to, greater than, or less than the change in volume during the second six months. The first-year accumulation rate wa s evaluated for the number of people in the home, the septic tank size, and th e capacity of the septic tank.

PAGE 62

49 Task 4: Interpretation of Phase I and Phase II Model Results The accumulation rates and performance vari ables were subsequently subjected to correlation analysis in order to quantify the influence of each pe rformance variable on OSTDS performance. The correlation analys is and model development were performed by Dr. Gary Stevens of the Biostatistics C onsulting Laboratory (BCL ) in the Department of Statistics at the University of Florida. The specific methods used are described below. Subtask 4A: Assess Sample Size The mean and standard deviation values of the linear accumulation rates were evaluated to determine if the sample size used was statistically significant. There are two considerations in determini ng the appropriate sample size: the tolerable error that establishes the width of the in terval and the level of confidence. The tolerable error was based on the smallest increment of measure. In most cases, a confidence interval of the mean was too wide. The solid accumulation is based on a vertical measurement and tank dimensions. However, the measurement is only accurate to -inch. A -inch error can cause error in the solid volume accumulation rate that can range fr om 0.002 to 0.009 gallons per day, depending on the tank dimensions. An average of po ssible accumulation rate error for each tank was used for the margin of error when calculati ng the significant sample size needed for a 95% confidence of the population mean. The sample size is calcu lated from Equation 33 (Ott and Longnecker, 2001). The sample size equation is based on an estimated standard deviation ( ), confidence interval ( ), the tolerable error (W), and the Z statistic (Z /2).

PAGE 63

50 (EQN 3-3) 2 2 2 2 /2 W Z n Subtask 4B: Assessment of Correlations Correlations determine if a relationship exists between two variables. A correlation was done for the potential performa nce variables to pred ict accumulation and trends. A correlation measures the strength of the linear relations hip between the two properties and the stronger a correlation is; th e better the variable is in predicting the accumulation. The relationship is determined by the coefficient of determination, rsquare. A value of zero indi cates that no predictive value in using the variable and a value of 1 indicates perfect predic tability (Ott and Longnecker, 2001). Correlation analysis to determine the relationships between the accumulation rates and performance variables was conducted using accumulation rates of all the systems together and using rates divide d into two specific groups. Dr. Stevens used the Statistical Analysis Software (SAS) to perform linear co rrelations of the performance variables to the accumulation rate. The two groups rates, termed as “excessi ve” and “not excessive,” were chosen based on the differences in accumulation observe d. Distribution plots provided a visual means of dividing the rates into these two categories. Subtask 4C: Assessment of Model Results The accumulation model was calculated by multiple linear regressions that relate the accumulation rate to a set of performan ce variables. The multiple regression model that best predicts the accumulation rate is indicated by the coefficient of determination. A coefficient of determination, r-square valu e, of 0.400 was the assumed cutoff value that

PAGE 64

51 shows a relation when correlating variable s, but a 0.700 was the cutoff value for a significant model. The r-square value used as the cutoff limit is based on the 0.6 being the minimum value that a scatter plot show s a relationship between the variables and accumulation rates. Using a 0.4 value for correlations ensures that all correlating variables will be included. A 0.700 value used as an r-square cutoff value makes the model have a mandatory relations hip without being too stringent

PAGE 65

52 CHAPTER 4 RESULTS AND DISCUSSION Task 1: Identification of Relevant Variables As discussed in Chapter 3, the purposes of th e literature review stage of this project were to not only to assess current knowledge of OSTDSs and their best management but also to identify any potential variables that may impact their performance. A large group of these “performance” variables were assembled and grouped into three basic categories, wastewater quality/hydraulics, systems design and condition, or the surrounding environment, as previously described. Figure 4-1 provides a breakdown of these variables into their respectiv e groupings. For example, occ upancy characteristics, the source and amount of water used, the type of water-using appliance, and the type of disposal practices may impact wastewater qualit y and hydraulics. It should be noted that, of all of products disposed of (solids and liquids) listed under Disposal Practices, none were considered in the mode ling portion of this project; however, information on these specific disposal activities (e.g., disposing of medications in the toilet) was collected from each participant via the surveys. Thes e activities provided a general overview of the awareness that the participants had on the impact of their activities on OSTDS performance.

PAGE 66

53 Number of residents Occupancy per year Length of time in home Age of residentsOccupancy Water source Water quantity usedWater Use capacity detergent loads Dishwasher capacity water-conserving detergent fabric softener bleach loads Washing Machine Garbage DisposalWater-Using Appliances Shower ToiletPlumbing Fixtures feminine products disposable diapers plastic products nylon medication rubber products coffee grinds cigarette filters food particles paper towels Solids paint thinner pesticides cooking oil sour milk disinfectants bleach sour milk LiquidsDisposal Practices Wastewater Quality and Hydraulics System Age Volume Chambers Number of tanks Average length Average widthSeptic Tank Area Configuration ElevationDrainfield Repairs Knows system's location Drives or parks on system Plants on system System additiveCare and Maintenance System Design and Condition Site Elevation Normal water table Seasonal High water tableWater Table Flooding Near surface water Surrounding Environment Potential Performance Variables Figure 4-1 Divisions of Performance Variab les into the Three Characteristic Groups These variables were broken down further into those that were quantitative in nature (requiring an actual numerical value) or qualitative in natu re (e.g., yes/no, on/off), as shown in Tables 4-1 to 4-3 for all three larger categories of variables. Those variables that were qualitative in nature were designate d by a “0” to represent “no,” or “off,” or a “1” to represent “yes,” or “on.” For exampl e, if the participants did not drive on their

PAGE 67

54 drainage location, this would be signified by a “0,” and, if their systems experienced flooding over the OSTDS after ra infall events, this variable was denoted by a “1,” meaning “yes.” In some instances, additional numbers were used for qualitative variables. For example, dishwasher capacity is a qualitative va riable used, where 0 signified that the homeowner does not have a dishwasher, 1 signified a compact capacity, and 2 signified a standard capacity. Table 4-1 Potential Performance Factors De scribing Wastewater Quality and Hydraulics Description* Data Type Quantitative Units Residents (R1) Quantitative Capita Residents under 11 years (R2) Quantitative Percent Residents 11 to 19 years (R3) Quantitative Percent Residents 20 to 69 years (R4) Quantitative Percent Residents over 70 years (R5) Quantitative Percent Occupancy (HM1) Quantitative Months/year Length in home (HM2) Quantitative Years Water Source (HD1) Qualitative 1/2/3 Water Consumption (HM21) Quantitative Gallons per day Dishwasher-Capacity (HD11) Qualitative 0/1/2 Dishwasher-Detergent (HM8) Qualitative 0/1/2/3/4 Dishwasher-Loads (HM7) Quantitative Loads/week Washing Machine-Capacity (HD9) Qualitative 0/1/2/3/4 Washing-Machine-Detergent (HM5) Qualitative 0/1/2/3 Washing Machine-Water Conserving (HD10) Qualitative 0/1 Washing Machine-Fabric Softener (HM6) Qualitative 0/1 Washing Machine-Bleach (HM4) Quantitative Cups/week Washing Machine-Loads (HM3) Quantitative Loads/week Garbage Disposal Use (HM9) Qualitative 0/1/2/3 Plumbing Fixtures-Toilet (HD5) Qualitative 0/1 Plumbing Fixtures-Showers (HD6) Qualitative 0/1 Disposal Practice-Solids (HM12) Qualitative 0/1 Disposal Practice-Liquid (HM13) Qualitative 0/1 Items in parenthesis are abbreviations used to denote these factors

PAGE 68

55 Table 4-2 Potential Performance Factors Describing System Design and Condition Description* Data Type Quantitative Units System Age (SD1) Quantitative Years Septic Tank –Volume (SD2) Quantitative Gallons Septic Tank – Chambers (SD3) Quantitative Chambers/tank Septic Tank –Quantity (SD4) Quantitative Tanks/home Septic Tank-Average Length (SD9) Quantitative Inches Septic Tank-Average Width (SD8) Quantitative Inches Drainfield-Surface Area (SD5 ) Quantitative Square Feet Drainfield-Configuration (SD6) Qualitative Drainfield-Elevation (SD7) Quantitative Feet Known Repairs to System (HD7) Qualitative 0/1 Care-System Location (HM10) Qualitative 0/1 Care-Drives or Parks on System (HM11) Qualitative 0/1 Care-Plants on System (HD8) Qualitative 0/1 CareSystem Maintenance (HM20) Qualitative 0/1 *Items in parenthesis are abbreviatio ns used to denote these factors. Table 4-3 Potential Performance Factor s Describing Surrounding Environment Description Data Type Qualitative Units Site Elevation Quantitative Feet Water table-Normal Quantitative Feet Water table-Seasonal Quantitative Feet Flooding of OSTDS After Rain Event Qualitative 0/1 Within 75 ft to surface water Qualitative 0/1 Task 2: Selection and Recruitment of Part icipants from a Select Population of Charlotte County OSTDS Owners Subtask 2A: Selection of Potential Participants As previously described, the CCGIS Depart ment used ARC GIS methods to locate OSTDSs throughout the county. Figure 4-2 shows a map of Charlotte County’s MidCounty Basin 2 (MC-2) of the selected hom es having OSTDSs. A total of 43,311 homes using OSTDSs in 2001 were located, and this database was layered with the county soil information to determine the amount of OSTD Ss for each soil type present in Charlotte

PAGE 69

56 County. Soil types with 2% or more of th e County’s OSTDS population were considered to be the “most populated” soil types (defined as those types with the greatest number of OSTDSs), and Table 4-4 shows those soil type s with the greatest number of OSTDSs. For a single soil type, the grea test number of systems (18.7%) was located in Oldsmar Sand with 8094 systems. In alignment with th e criterion that the project focus on systems in these “most populated” soils potential partic ipants were subsequently randomly selected from these areas in MC2. Table 4-4 “Most Populated” Soils (with La rgest Number of OSTDSs) in Charlotte County Soil ID Soil Name County Population Percent of Population 36 Immokalee-Urban Land Complex 1866 4.2 % 43 Smyrna Fine Sand 4009 9.3 % 11 Mayakka Fine Sand 2451 5.7 % 28 Immokalee Fine Sand 3887 9.0 % 69 Matlacha gravelly fine Sand 2531 5.8 % 26 Pineda Fine Sand 2747 6.3 % 7 Matlacha-Urban Land Complex 6005 13.9 % 33 Oldsmar Sand 8094 18.7 % 12 Fedla Fine Sand 1114 2.6 % 13 Boca Fine Sand 4425 10.2 % 34 Malabar Fine Sand 1341 3.1 % 42 Wabasso Sand, limestone substratum 2931 6.8 % Subtask 2B: Recruit Participants Because many of the addresses of the randomly selected homes obtained from the ARC GIS database were not upda ted or did not contain OSTD Ss or even homes, it was necessary to repeatedly select new particip ants and mail initial information concerning this program (see Appendix A). Another me thod of approaching potential participants was by recruiting methods, as previously disc ussed. Recruitment e nded in June of 2002 with a total of 292 willing residents. Table 4-5 illustrates the number of participants from

PAGE 70

57 Figure 4-2 Selected Homes having OSTDSs within Mid-County-2

PAGE 71

58 each recruitment event. All volunteers who approached CCDOH after hearing or reading advertisements or who were recruited duri ng initial inspections of neighboring homes (except the ones recruited from the county fair) were combined with the randomly selected group for the mailing campaign. At one participant’s home during the inspection, five interested neighbors joined the study and had their systems inspected and pumped the same day. The best recruiting method was by face-to-face contact (at the fair and during inspections), and th e fair booth also enabled co ntact with residents that received information from the mailing campaign. Table 4-5 Recruitment Results Recruitment Event No. Recruited Participants Mailing Set #1 32 Mailing Set #2 15 Mailing Set #3 61 County Fair 98 Mailing Set #4 51 Mailing Set #5 35 Total 292 At the end of the first inspection, 238 pa rticipants remained in the study. The 54 participants that were no longe r in the study either withdrew or were not eligible because of the condition of their system or the conversi on to sewer in the next year. At the end of the 12 months, 221 participants remained with 179 in Phase 1 and 42 in Phase 2. The 29 participants dropped from the program be tween June 2002 and June 2003 because tank information could not be obtained (preventing vo lumes to be calculated), system failures, or the property owner had their system pumped during the study. During the initial inspections by the CCDOH, 25 percent of the systems needed repairs. Ten percent of the systems had broken off or missing outlet tees. Seventeen

PAGE 72

59 percent of the systems had bad seals between either the manhole and th e lid or the lid and the top of the tank. Ten per cent of the systems had holes in the tank, a result of the sulfate content of the wastewater enteri ng into the septic ta nk, where anaerobic conditions, high-strength wa stewater, low-flow veloci ty, and long retention time promotes the production of H2S, thus leading to the corrosion of tank walls (Fan et al., 2001). Subtask 2C: Separation of Recruits into Phase 1 and 2 As mentioned previously, 221 residents were recruited or volunteered to participate in this study, as a re sult of the vigorous recruiting and advertising campaigns. Of this total count, 42 were selected to participate in Phase 2, designed specifically to validate the results of Phase 1. As a result, their sy stems were initially in spected and pumped out subsequent to the Phase 1 systems. The distribution of the collected quantita tive and qualitative data obtained for all 238 initial recruits and their systems is presented in Tabl es 4-6 and 4-7. As previously described, care was taken in separating Phase 1 and 2 groups to maintain these percentage breakdowns of the number of sy stems in the low and high ranges of each factor. For example, as shown in Table 4-6, the percentage of all homes with 1-2 occupants was 63% ((149/238)*100), and this wa s the target percentage used in both Phases 1 and 2, as shown in Table 4-8 with 125 out of 198 for Phase 1 and 24 out of 40 for Phase 2. The median number of occupants per house was 2, and each home prepared a median number of washing machine and dishwa sher loads of 4 and 2, respectively (Table 4-6). Of interesting note in Table 4-7 is th e large number of system s with plants on or near the drainfield, flooding, drainage from the washing machine, and the large numbers

PAGE 73

60 of occupants who dispose of liquids and solid s down their sink drains. On the other hand, 46% of the participants had water-conserving toilets and showerhead s, and 95% reported to have knowledge of the location of thei r OSTDSs. Refer to Appendix C for further detail on the separation of the recruits into the 2 phases. Table 4-6 Distribution for Quantitative of Household Characteristic for All Recruits Factor ID Factor Count Median Low Value Range Low Count High Value Range High Count R1 People per home 238 2 1-2 149 3-12 89 HM1 Time of Occupancy (months) 238 12 0-11 19 12 219 HM3 Washing machine loads 238 4 0-4 121 5-28 117 HM7 Dishwasher loads 238 2 0-2 123 3-10 114 Table 4-7 Distribution for Qualitative of H ousehold Characteristics for All Recruits Factor ID Factor Count Qualitative Factors City WellBoth HD1 Water Source 238 195 35 8 Qualitative – Yes/No No Yes HD2 Washing machine drains to septic tank 238 33 205 HD5 Water-conserving toilets 235 126 109 HD6 Water-conserving showers 235 126 109 HD7 System repair or replacement 234 97 137 HM10 Location knowledge 237 10 226 HM11 Parking or driving on system 237 235 2 HD8 Plants on drainfield 235 153 81 E5 Systems within 75’ of surface water 236 219 17 HM12 Disposal of liquids 238 121 117 HM13 Disposal of solids 238 63 174 E4 Flooding 238 22 216 Subtask 2D: Data Collection and Databasing As previously described, the independent variables to be used in the modeling phase were obtained from an initial and follow-up survey, permits, and inspections. The initial survey was successfully completed and returned from the participants, and the

PAGE 74

61 Table 4-8 Frequencies for Each level of Household Characteristics for Each Phase follow-up survey was completed and returned by all but 27 particip ants. Many of the participants had to be cont acted in person or by telephone to have the follow-up survey completed. Permits were not available for 6 participants; therefore, their systems had missing factor data for the system design and surrounding environment factors. The height measurements used for the dependent vari able in the subsequent statistical analysis were gathered during inspect ions approximately 6 and 12 months after pump out, as previously described. One home’s OSTDS was not measured at 6 months because the water consumption was less than 200 gallons. All data, both the solids management and performance factors, were transferre d and stored in an Access database. Factor ID Phase 1 Phase 2 Low High Low High R1 125 73 24 16 HM1 17 181 2 38 E4 179 19 37 3 HM3 103 95 18 22 HM7 100 98 23 17 City Well Both City Well Both HD1 164 29 7 31 8 1 No Yes No Yes HD2 30 168 3 37 HD5 105 90 21 19 HD6 83 111 14 26 HD7 181 10 38 2 HM10 7 190 3 37 HM11 196 1 39 1 HD8 127 68 26 14 E5 184 12 35 5 HM12 51 147 12 28 HM13 100 98 21 19

PAGE 75

62 Task 3: Calculation of Solids Accumulation Subtask 3A: Calculation of Tank Dimensions Of the total of 221 tanks studied, 27 did not have readily available dimension information, thus necessitating calculation of th ese parameters. As previously described, two methods were used to calculate dime nsions. Method 1 simply required the tank volume and liquid height and was used for calculating dimensions of 5 tanks with volumes less than 600 gallons. Method 2 was more complex (and, perhaps more accurate) using dimension ratios and was us ed on the remaining 22 tanks with volumes greater than 750 gallons. The manufacturer ’s tank dimensions and the estimated dimensions using the two methods described above are presented in Appendix D of this document. Subtask 3B: Calculation of Solid Volumes Septic Tank The tank dimensions and measured hei ghts of liquid, scum, and sludge taken during inspections were subse quently used to calculate solids volumes after 6 and 12 months of accumulation time. Tables 4-9, 4-10, and 4-11 provide the scum, sludge, and total solid volumes accumulated along with their accompanying standard deviations and coefficients of variation. The mean scum accumulation during the first 6-month period was 6.1 gallons, ranging from 0 gallons (in 58 tanks) to 90.7 ga llons (in 1 tank). Considering the 12month scum data, the mean accumulation increa sed to 9.4 gallons, showing that the rate of accumulation during the latter 6 months wa s somewhat lower than the first 6 months; however, care should be taken in making conclu sions given the magnitude of the standard deviations. A similar trend was observed for th e sludge. The more critical time period in terms of accumulation appears to be during th e months immediately following pump out.

PAGE 76

63 Why faster rates in accumulation occur in the earlier stages is not known; however, it can be surmised that the biological community is not well established and less capable of solid degradation soon after pump out as repo rted in the Bounds (1996) study. The mean total solids volume increased after 12 months to 49.4 gall ons, or 9.8% of the smallest tank volume and 3.3% of the largest tank volume. Table 4-9 Scum Volume 6 a nd 12 Months After Pump out Accumulation (Gallons) Mean Standard Deviation Coefficient of Variation 6 months 6.1 13.2 2.15 12 months 9.4 17.6 1.88 Table 4-10 Sludge Volume 6 and 12 Months After Pump out Accumulation (Gallons) Mean Standard Deviation Coefficient of Variation 6 months 28.5 24.1 0.845 12 months 41.1 29.8 0.726 Table 4-11 Total Solids Volume 6 and 12 Months After Pump out Accumulation (Gallons) Mean Standard Deviation Coefficient of Variation 6 months 34.3 26.7 0.779 12 months 49.4 33.2 0.673 Subtask 3C: Calculation of Accumulation Rates The accumulation rate for scum, sludge, and total solids was calculated. The accumulation rate for the solids was calculated for 0-6 months, 6-12 months, and 0-12 months by dividing the volume data by the appropriate time period. The accumulation rate was also calculated on a per person basis. A linear accumulation rate per system and a linear accumulation rate per person were dete rmined for the first year of service, which used the 6and 12-month measurements. The number of people in a home, the tank

PAGE 77

64 volume, and the tank capacity were evaluated to determine if these variables would affect the accumulation rate. Accumulation rate per system The accumulation rate for scum, sludge, and total solids during the first six months, second six months, and one year are presente d in Tables 4-12, 4-13, and 4-14. The accumulation rate during the second six months of service is less than the accumulation rate during the first six months. Scum accu mulation in the second six months is about two-thirds as the first six months, while sludge accumulation in the second six months is less than half than the first six months. Table 4-12 Scum Accumulation Rates Accumulation (Gallons/Day) Mean Standard Deviation Coefficient of Variation 0-6 months 0.031 0.066 2.170 6-12 months 0.019 0.071 3.810 0-12 months 0.025 0.048 1.849 Table 4-13 Sludge Accumulation Rates Accumulation (Gallons/day) Mean Standard Deviation Coefficient of Variation 0-6 months 0.141 0.121 0.86 6-12 months 0.072 0.120 1.82 0-12 months 0.109 0.078 0.70 Table 4-14 Total Solids Accumulation Rates Accumulation (Gallons/day) Mean Standard Deviation Coefficient of Variation 0-6 months 0.171 0.134 0.791 6-12 months 0.091 0.137 1.621 0-12 months 0.134 0.086 0.670 The accumulation rates of the measured solids during the first year determined by linear regression are presented in Table 4-15. Compared to the “r ise over run” method

PAGE 78

65 used to calculate the data in Tables 4-11, 4-12, and 4-13, these values are quite similar with relatively large R2 values (a measure of goodness of fit). Table 4-15 Scum and Sludge Accumulation Rate Data Determined Using Linear Fits Accumulation (Gallons/day) Slope Standard Deviation Coefficient of Variation R2 Mean Scum 0.011 0.020 1.818 0.564 Sludge 0.116 0.082 0.707 0.825 Total Solids 0.142 0.089 0.627 0.853 Accumulation rate per person The accumulation rates for the solids were also normalized on a per person basis for each time interval, and thes e values are presented in Tables 4-16, 4-17, and 4-18. Table 4-19 presents the accumulation rates de termined using linear fits and normalized on a per person basis. Table 4-16 Scum per Person Accumulation Rate Accumulation (Gallons/day/capita) Mean Standard Deviation Coefficient of Variation 0-6 months 0.010 0.020 1.978 6-12 months 0.007 0.026 3.735 0-12 months 0.009 0.016 1.909 Table 4-17 Sludge per Person Accumulation Rate Accumulation (Gallons/day/capita) Mean Standard Deviation Coefficient of Variation 0-6 months 0.062 0.055 0.883 6-12 months 0.032 0.058 1.967 0-12 months 0.048 0.039 0.835 Table 4-18 Total Solids per Person Accumulation Rate Accumulation (Gallons/day/capita) Mean Standard Deviation Coefficient of Variation 0-6 months 0.072 0.056 0.778 6-12 months 0.039 0.062 1.706 12 months 0.057 0.040 0.723

PAGE 79

66 Table 4-19 Accumulation Rates of Solids pe r Person Determined Using Linear Fits Accumulation (Gallons/day/capita) Slope Standard Deviation Coefficient of Variation R2 Mean Scum 0.004 0.007 1.817 0.562 Sludge 0.050 0.040 0.791 0.825 Total Solids 0.060 0.040 1.024 0.853 Subtask 3D: Trends in Accumulation Accumulation trends during the first year The accumulation trends were evaluated by comparing the change in solid volumes during the first and last 6-month periods. Table 4-20 provi des the number of systems that showed an increase, decrease, or no change in scum and sludge volumes from the first to the last 6-month period, a nd Table 4-21 shows the number of systems in which the accumulation rate changed from th e first and last 6 month periods. Volumes that remained the same or decreased from 6 months to 12 months were considered to have a decreasing accumulation rate, as show n in Table 4-21. Of the 140 systems that had decreased scum accumulation rate, only 17 systems increased in scum volume after 6 months. While 145 systems experienced a decrease in sludge accumulation rate, only 71 systems experienced an increased volume. A ma jority of those systems with decreases in accumulation rate did not experience an incr ease in the accumulation volume. The result of this lack of accumulation after 6 months shows that th e systems’ accumulation rates begin to decrease after 6 months for just over half of the participants. Table 4-20 Solids Volume Change from 6 months to 12 months No. of Phase 1 Systems No. of Phase 2 Systems Scum Sludge Scum Sludge Decrease 44 40 8 9 No Change 60 22 11 3 Increase 75 117 23 30

PAGE 80

67 Table 4-21 Solids Accumulation Rate Ch ange from 6 months to 12 months No. of Phase 1 Systems No. of Phase 2 Systems Scum Sludge Scum Sludge Rate Increase 62 60 19 16 Rate Constant or Decrease 117 119 23 26 Phase 1 had 18 participants and Phase 2 had 6 participants with tanks where scum and sludge accumulation rates increased during the second 6 months compared to the first 6 months. A total of 51 part icipants’ tanks showed a decr ease in scum volume, and 44 participants’ tanks had a decrease in sludge volume during the second six months. The decreasing accumulation of solids in the first y ear is not likely to be caused by microbial degradation, as it has been reported that mi crobial activity impacts the accumulation rates only after two years (Bounds, 1996) Sludge settling resulting in an increase in density may cause the decrease in sludge volume. Accumulation trends in relation to people and sept ic tank volume The linear accumulation rate at one year was analyzed based on number of people in the home, volume of the septic tank, and septic tank capacity. The septic tank capacity was calculated by dividing the total tank volum e by the number of pe ople in the house. The mean and standard deviation were de termined for each set of accumulation rates within each level of number of people per home (Table 4-22), septic tank volumes (Table 4-23), and septic tank capacity (Table 4-24) The accumulation rates of scum and sludge were plotted against the number of people, the septic tank volume, and the septic tank capacity (Figure 4-3 to Figure 4-5, respectively). The accumulation rates based on the number of people in the home graphically show that the accumulation rate increases as the number of people increase

PAGE 81

68 Table 4-22 Accumulation Rates Based on the Number of People in the Home Number of People Solids CountMean Standard Deviation Coefficient of Variation 1 Scum 28 0.0060.009 1.482 Sludge 28 0.0730.054 0.741 2 Scum 107 0.0160.036 2.345 Sludge 107 0.1160.077 0.665 3 Scum 33 0.0270.030 1.115 Sludge 33 0.1190.064 0.536 4 Scum 33 0.0560.080 1.429 Sludge 33 0.1210.098 0.808 5 Scum 13 0.0540.055 1.010 Sludge 13 0.1030.060 0.577 6-10 Scum 7 0.0580.072 1.242 Sludge 7 0.1810.174 0.962 for both scum and sludge. The accumulation rate s for both solids were statistically tested using the t-test to determine if the accumula tion rate means increased with occupants. For the sludge accumulation rate, the accumulation rate beyond 2 or more people was statistically the same. However, an in crease in the sludge accumulation rate was statistically significant once there was more than 1 occupant in the home. The scum accumulation rate statistically increased for each occupant from 1 to 4 occupants in the home. For 4 or more occupants in the home the scum accumulation ra te was statistically the same. The increase in accumulation based on number of people in the home may be a result of a higher volume of solids entering into the septic tank. The accumulation rate based on septic ta nk size graphically showed that solids accumulation increased as the septic tank volume increased. The accumulation rates were statistically tested using the t-test to determine if the accumulation rate means increased with the larger volume septic tank s. The sludge accumulation rate increased for septic tank volumes larger than 750 gall ons when compared to smaller tanks. The scum accumulation rate showed to not be st atistically different for any septic tank

PAGE 82

69 y = 0.0112x 0.0042 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0246810 People per HomeScum Accumulation Rate (Gallons/day) Scum Mean Scum Values Linear (Scum Values) A y = 0.0137x + 0.0764 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0246810 People per HomeSludge Accumulation Rate (Gallons/day) Sludge Mean Sludge Values Linear (Sludge Values) B Figure 4-3 Accumulation Rate Trends Based on number of People in the Home A) Scum Accumulation B) Sludge Accumulation Table 4-23 Accumulation Rate Based on Septic Tank Volume Tank Volume (gallons) Solids CountMean Standard Deviation Coefficient of Variation <750 Scum 6 0.0120.020 1.654 Sludge 6 0.0600.066 1.107 750 Scum 54 0.0200.049 2.460 Sludge 54 0.0850.062 0.723 900 Scum 136 0.0240.044 1.811 Sludge 136 0.1230.080 0.651 >900 Scum 25 0.0480.065 1.358 Sludge 25 0.1280.107 0.835

PAGE 83

70 y = 6E-05x 0.0274 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 400600800100012001400 Septic Tank Volume (Gallons)Scum Accumulation Rate (Gallons/day) Scum Mean Scum Value Linear (Scum Value) A y = 0.0002x 0.0757 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 400600800100012001400 Septic Tank Volume (Gallons)Sludge Accumulation Rat e (Gallons/day) Sludge Mean Sludge Value Linear (Sludge Value) B Figure 4-4 Accumulation Rate Trends Base d on Septic Tank Volume A) Scum Accumulation B) Sludge Accumulation volume. The increase of solids accumulation with respect to septic tank size is likely retention of more solids by larger tanks than compared to smaller tanks. The septic tank capacity was plotted to furt her evaluate the previous two results. The scum accumulation trend graphically shows that, as a system increased in capacity, a larger tank with fewer residents, the accumulation of scum decreases and sludge accumulation has an overall decreas ing pattern. The t-test was us ed to statistically test if the accumulation rates decreased as septic tank capacity increased. The sludge

PAGE 84

71 Table 4-24 Accumulation Rate ba sed on Septic Tank Capacity Tank Capacity (gallons/person) Solids CountMean Standard Deviation Coefficient of Variation <200 Scum 21 0.0480.052 1.092 Sludge 21 0.1290.054 0.741 201-250 Scum 27 0.0580.084 1.447 Sludge 27 0.1230.107 0.871 251-300 Scum 13 0.0450.060 1.131 Sludge 13 0.1020.059 0.584 301-350 Scum 26 0.0260.030 1.131 Sludge 26 0.1270.063 0.493 351-400 Scum 32 0.0200.059 2.903 Sludge 32 0.0910.064 0.699 451-500 Scum 70 0.0140.021 1.524 Sludge 70 0.1250.079 0.630 501-550 Scum 4 0.6070.009 1.358 Sludge 4 0.1370.097 0.702 701-750 Scum 14 0.0050.008 1.810 Sludge 14 0.0610.044 0.719 851-900 Scum 13 0.0080.010 1.217 Sludge 13 0.0910.060 0.660 accumulation rate was inconclusive. The scum accumulation rate was shown to increase with decreasing septic tank cap acities. The preliminary trends in accumulation show that accumulation decreases when larger septic tanks and fewer people are taken into consideration. Task 4: Interpretation of Phas e 1 and Phase 2 Model Results Subtask 4A: Assess Sample Size As previously described, the number of par ticipants finally chosen for this study was restricted to a total number that would accommodate a severely limited number of CCDOH staff assigned to pump out and solids measurement duties. The final number of

PAGE 85

72 y = -7E-05x + 0.0554 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 4006008001000 Septic Tank Capacity (Gallons/person)Scum Accumulation Rate (Gallons/day) Scum Mean Scum Value Linear (Scum Value) A y = -7E-05x + 0.1394 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 4006008001000 Septic Tank Capacity (Gallons/person)Sludge Accumulation Rate (Gallons/day) Sludge Mean Sludge Value Linear (Sludge Value)B Figure 4-5 Accumulation Rate Trends Base d on Septic Tank Capacity A) Scum Accumulation B) Sludge Accumulation systems studied was 221. In order to assess whether this number was significantly high enough to represent all of the Charlotte C ounty systems (and, therefore, produce robust, statistically significant results), the smallest significant sample size was calculated using the sludge and scum accumulation rates determ ined by linear fits. Table 4-25 presents values of significant sample sizes for bot h accumulation rates, along with parameters used to estimate these values. The tolerabl e error was a conservative value that accounts

PAGE 86

73 for the average error of each measurement by using the smallest increment of measure on each side of the mean as the width. This average “smallest increment of measure” was determined by taking the average gallons of solids at a quarter of an inch and dividing by 365 days calculated the average smallest increment of measure. The Z /2 term, taken from the tabulated values (Ott and Longn ecker, 2001), is the area under a normal curve for a 95% confidence interval. Table 4-25 Significant Sample Size Values Solids Significant sample Size Mean Standard deviation Average Smallest increment Tolerable error Z /2 Scum 150 0.026 0.048 0.008 0.015 1.96 Sludge 526 0.114 0.08 0.007 0.014 1.96 The sample size used in this study of 221 systems is sufficien t to provide robust analysis of scum accumulation but falls shor t for sludge accumulation. Therefore, care should be taken in interpreting th is latter data. It is important to note here that there was no freedom to add additional par ticipants in this study. The primary reason for this lack of freedom was the previously mentioned inability of CCDOH to perform individual pump outs and measurements beyond the final number 221. Also, because this project was constrained by fixed deadlines set by FDEP and CCDOH in their original agreement, new participants could not be added once Phas e 1 of the project had begun. Despite not having a sample size significantly sufficient to warrant robust co rrelation of sludge accumulation with collected performance variab les, meaningful trends between the two variable types were still discerned.

PAGE 87

74 Subtask 4B: Development of Correlations Correlations of the potential performance variables to the solids accumulation rates were constructed to determine thei r influence on system performance. As mentioned previously, the Statistical Analys is Software (SAS) was used to construct multiple linear and linear correlations. The robustness of the correlations was initially judged based on R2 values, where 0.7 was arbitrar ily set as a cutoff value. If a correlation between the solids accumulation rates a nd performance variable(s) was not shown to have a high enough R2 value (and corresponding low p value), evidence of influencing trends betw een the rates and performan ce variable was assessed. A performance variable was determined to ha ve significant influence on an accumulation rate if the probability value (or p value) was less than 0.05. The p value is the portion of the population that will not be includ ed in the statistical prediction. The MLR analysis using the scum, sludge, and total solids accumulation over 6 and 12 months did not result in correlations of statistical significance (with r-square values greater than 0.7). However, consistent tr ends between the independent performance variables and the dependent accumulation rates were observed by the correlation’s p values less than 0.05. While a p value of le ss than 0.1 was deemed as significant but not statistically. Sludge accumulation rate correlations Excessive sludge accumulation, defined as an accumulation rate greater than 2.41 x 10-4 gallons per person per day, was impacted by the washing machine activity (specifically machine capacity, use of a wa ter-conserving model, detergent type, and drainage) during the first six months. The severe sludge accumula tion appeared when using liquid detergent, a large or extra la rge capacity, water-cons erving (front-loading)

PAGE 88

75 washing machine that drains to the septic tank. The washing machine detergent, washing machine drainage, type of water-conservi ng washing machine model, and the washing machine drainage were the only factors to noticeably correlate w ith sludge accumulation during the first six months. The scatter plot s in Figure 4-6 show the trends for washing machine capacity, water conserving models, washing machine detergent, and washing machine drainage against the sludge accumula tion rate at 6 months. After one year, excessive sludge accumulation did not significantly correlate to any of the variables. The variables, use of low-flow showerheads, a nd the presence of plants on the drainfield showed trends influencing sludge accumulati on, but the resulting co rrelations were not statistically significant. Scum accumulation rate correlations Unlike what was observed with the exce ssive sludge accumulation, excessive scum accumulation, defined as an accumulation greater than 4.11 x 10-5 gallons per person per day, correlated well with some performance va riables using the 12-month data but not the 6-month data. Using accumulation rates at 6 months, only the occurrence of flooding correlated with the scum accumulation rate since the probability was less than 0.10, but was not statistically significan t since it did not have a pr obability of less than 0.05. However, only 14 participants reported floode d conditions in their OSTDS area, leaving this result in question. Correlations between the 12-month data a nd performance variables showed that garbage disposal use, washing food down th e sink drain, dishwasher detergent and washing machine capacity significantly influenc ed the rate of scum accumulation. The most significant correlation was obtained with the capacity (large-t o-extra-large) of washing machine (p=0.0017). As a matter of fact, 62% of the participants with

PAGE 89

76 “excessive” scum used large-to-extra-large capacity washing machines. The dishwasher detergent type showed an influencing tr end with a probability of 0.0437. Sixty-one percent of the participants with excessive scum accumulation used liquid detergent, compared to participants that did not have excessive scum accumulation (37% of whom used liquid detergent). Furthermore, 43% of participants that did not have excessive scum accumulation used powder detergent, a nd 28% for excessive scum accumulation. Likewise, garbage disposal use yielded a si gnificant correlation with the 12-month scum accumulation rates (p=0.0245) with 74% of the participants that experienced excessive scum accumulation regularly used their garbage disposal. Whether a participant disposed of food scraps on their dishes before wash ing influenced scum accumulation (p=0.0168), and it was found that 46.4% of those partic ipants that experienced excessive scum accumulation did not scrape their dishes before rinsing. When pooling Phase 2 data with Phase 1 data, the use of low-flow show erheads was shown to decrease scum accumulation with 68.5% of the participants that did not have excessive scum accumulation used these showerheads. The scatter plots further illustrate the trend in scum accumulation for these performance variables (Figure 4-7). Solids disposal and flooding trends influe nced excessive scum accumulation at 12 months, but the resulting correla tions were not statistically si gnificant. The practice of improper solids disposal showed an influe ncing trend for scum accumulation (p=0.0561) with 63% of participants that had excessi ve scum accumulation improperly disposed of solids while 44.8% of participants that did not have excessive accumulation also improperly disposed of solids. The o ccurrence of flooding, ag ain, correlated with excessive scum accumulation with a p value of 0.0711. Although, only 15.2% of

PAGE 90

77 participants that had excessive scum accumulation experiencing flooding and 5.6% of who do not have excessive scum accumula tion experience flooding. The low percent value does not seem evident in supporting the significant of flooding at 12 months. Subtask 4C: Development of Model Results A model was attempted for both solids at six months and at one year. At six months, the largest R2 achievable was 0.405 using all the potential performance variables, and the largest R2 at one year was 0.56 using all the potential performance variables. The inability to produce a model from the data is a result of both too few data points and the large amount of variability present in the soli ds measurements. The short time in which these measurements were collected most lik ely is not long enough to adequately measure system performance.

PAGE 91

78 0 0.15 0.3 0.45 012B 0 0.15 0.3 0.45 01234ASludge Accumulation Rate at 6 month s (gallons/capita/day) 0 0.15 0.3 0.45 0123CSludge Accumulation Rate at 6 month s (gallons/capita/day) 0 0.15 0.3 0.45 01D Figure 4-6 Scatter Plots for Sludge Accumula tion Rates at 6 Months with the lines representing the trend A) Washing M achine Capacity (0 = No Washing Machine; 1 = Compact; 2= Medium; 3 = Large, 4 = Extra Large) B) Water Conserving Model (0 = No Washing M achine; 1 = Top-loading; 2 = Frontloading) C) Washing Machine Detergent (0 = No Washing Machine; 1 = Liquid; 2 = Powder; 3 = Both) D) Wash ing Machine Drainage (0 = Does Not Drain to OSTDS; 1 = Drains to OSTDS)

PAGE 92

79 0 0.1 0.2 0.3 0.4 0123AScum Accumulation Rate at 1 2 months (gallons/capita/day) 0 0.1 0.2 0.3 0.4 1234B 0 0.1 0.2 0.3 0.4 0123CScum Accumulation Rate at 1 2 months (gallons/capita/day) 0 0.1 0.2 0.3 0.4 01234D Figure 4-7 Scatter Plots for Scum Accumula tion Rates at 12 Months with the lines representing the trend A) Garbage Di sposal Use (0 = Not Applicable or Never; 1 = Occasionally; 2 = After Di nner; 3 = Always) B) Food Down Sink Drain (1 = Food is Scraped from Plates and the Sink is Strained; 2 = Food is Scraped from Plates and the Sink is Not Strained; 3 = Food is Not Scraped from Plates and the Sink is Strained; 4 = Food is No t Scraped from Plates and the Sink is Not Strained) C) Dishwasher Detergent (0 = Dishwasher is Not Used; 1 = Liquid; 2 = Powder ; 3 = Both ) D) Washing Machine Capacity (0 = No Washing Machine; 1 = Compact; 2 = Medium; 3 = Large; 4 = Extra Large)

PAGE 93

80 CHAPTER 5 SUMMARY AND CONCLUSIONS The primary goals of this project were to determine what characteristics of household activities, system design, and environmental conditions impact the performance of OSTDSs to a significant extent and to provide CCDOH with a list of recommended changes to current practices in OSTDS management by Charlotte County residents. A secondary goal was to deve lop a model to allow prediction of solids accumulation over time. In order to achie ve these goals, data on current OSTDS practices, systems, and environmental condi tions were obtained by means of surveys, existing state/county documentation, and insp ections, and then ev aluated against the accumulation rate determined from measurements taken at 6 and 12 months. The budget and time restrictions limited the sample size to be 300 or less participants. Although, extreme efforts were taken to recruit OSTDS using homeowners, only 221 residents were willing and qualified to participate. All data collected through out the study were databased to maintain the data, while being able to be easily converted into a useable format for statistical analysis. The solids measurements at 6 and 12 mont hs from pump out were converted into sludge and scum volumes using the specific septic tank dimensions. The accumulation rates were calculated using the number of days between measurements, and the accumulation rates were determined with linear f its to take into account for the change in the accumulation rate through out the year.

PAGE 94

81 In order to best determine the that ch aracteristics of household activity, system design, and environmental conditions impact on the accumulation rates, the performance variables were linearly correlated against th e accumulation rates. The linear correlation between the accumulation rate and a specifi c performance variable assesses the relationship between the two. The performance variable s that correlate to the accumulation rates were used to develop a m odel for predicting the accumulation rates. Before a model is created, the performance variables were related to the accumulation rate using multiple linear correlations. An R2 value is determined for that multiple linear correlation, when the R2 value is less than 0.7 a significant model cannot be predicted using only these performance variables. The resulting conclusions at one year are that scum and sludge accumulation was too random to be used in creating an a ccumulation model for predicting pump out frequencies. Trends in sludge accumulation pr oved to be ineffectively significant with the inadequate sample size. The number of participants for scum accumulation trends was significant enough. Scum accumulation rates showed to be impacted by wastewater quality and hydraulic characteristics than system design and environmental conditions. During correlations with the performa nce variables, the scum accumulation rate at 12 months significantly related to the freque nt use of garbage disposals, allowing food particles to be disposed of down the sink drain, the wash ing machine capacity, and the dishwasher detergent.. Sludge accumulation did not have an adequate sample size, resulting in an inconclusive statistical analysis.

PAGE 95

82 While some potential variables were si gnificant in the study, other performance variables were not, possibly because of the short measurement period of one year may not provided enough time to completely charact erize system performance. Previous studies used a time period of up to eight years. The increase of solids accumulation during the last six months showed that for these systems the maximum accumulation rate in these systems did not occur within the first year of service. While not completely understood, the cause of the dras tic decrease in solids volumes from six to 12 months of service was possibly caused by system failure unexpected early microbial activity, or settling of stored solids, resulti ng in a denser sludge blanket. The variables that significantly impacted accumulation rates of scum and sludge are the following: Washing machine capacity; Garbage disposal use; Low-flow showerheads; Direct disposal of food particles; Washing machine detergent; Water-conserving washing machine model; Flooding. Given the trends observed with the above-m entioned household activities, the following practices are recommended to ensure optim al performance of OSTDSs in Charlotte County: Promote use of water-conserving fixtures and appliances; Discourage the use of unnecessary over-sized capacity washing machines; Limit garbage disposal use to extend the pump-out interval; Encourage occupants to limit the amount of solids and foods particles that exit through the drain and en ter the septic tank; Promote unsaturated soil conditions to prevent high ground water levels from infiltrating into the septic tank vi a the drainfield or leaky tank.

PAGE 96

83 The results of this study have potential to significantly impact the public health of Charlotte County residents by ensuring preven tion of pollution from OSTDSs into its numerous water bodies. Pr oviding information concerni ng the effects of certain household activities on system performan ce to OSTDS owners would result in a heightened awareness of the impact of thei r activities not only on th eir system behavior (and frequency of pump-outs) but also on the health of the surrounding environment. Given that the literature has reported that th e majority of system owners are unaware of these connections and that many of the part icipants polled in this study were also unaware of appropriate maintenance procedures, transfer of this information to the public is imperative.

PAGE 97

84 CHAPTER 6 RECOMMENDATIONS FOR FUTURE WORK The work performed in this study is vita l for the improvement of management and maintenance for OSTDSs. Further analysis of accumulation rates will help lead the progress for OSTDS management and ultimatel y, public and environment health. The purpose of this chapter is to provide recommen dations for future studies that may attempt to extend this project or repeat the methods reported herein. The results and conclusions brought forth from this study show that da ta collection is among the most important aspect for the analysis of solids accumulation. A majority of the recommendations to follow will discuss the importance of various aspects of sample size, monitoring of accumulation, and collection of pe rformance variables collected. Identification of Relevant Variables In this study, three major groupings were used to identify potential performance variables. In identifying variables for this study, anything that c ould possibly impact a accumulation was gathered, thus resulting in a large set of independent variables with unknown links to wastewater generation. Add itional research of each variable and its possible relationship to wastewater gene ration may have provided more informaed insight in development of survey questions. An example of this in this study is garbage disposal use. Given that a cl oser study of the variability that exist in use of garbage disposals, the different levels of use (nev er, occasionally, only afte r meals, and always) could have been more accurately defined. In doing so, the survey questions could have

PAGE 98

85 been better posed to elicit more accurate responses and, ultimately, more robust correlations. Selection, Recruitment, and Monitoring of Participants Other factors to consider in studies such as these include the ability to monitor solids accumulation over the enti re pump out interval and to obtain a significant sample size. Monitoring over the entire pump out inte rval will create a model that describes the accumulation that determines the need to pe rform maintenance pumping. An adequate sample size will ensure that the statistical analysis performed will bring forth more meaningful results. The sample size n eeded for this study over one year was 150 participants for scum accumulation and 526 participants for sludge accumulation. However, it is important to remember that the sample size required could change for different monitoring periods. Participant Selection The participants used in an accumulation ra te study should be selected on the basis of soil type, tank size, and number of occupa nts. Selecting part icipants based on the designated soil type is viable if it is possible to recruit strictly from the desired soil types. Participant selection should use a nested de sign based on number of people in the home and the septic tank size. (Further informati on on nested design can be found in statistical experimental design textbooks.) Participan ts should have available septic tank manufacture and dimensions with no current failures. Recruiting Participants The most successful recruitment technique was the booth at the county fair. The booth allows initial questions to be answered that would otherwise i nhibit residents from participating. If mailing is desired, using a two-part postc ard that can be mailed and a

PAGE 99

86 portion of it returned that is sent to every potential participant in the desired area is recommended. A two-part postcard would allow the study to be introduced to the prospective participants, and the returned portion can provide information on the number of occupants, contact information, and ot her information needed before collecting performance variable data. The two-part postcard would save both time and money (especially since survey packets would onl y be sent to interested recruits). Division of Recruits for Two Groups Maintaining two groups, one for creating a predictive model and the second for validating the model, is recommended. Usi ng the nested design discussed above would prevent the need to separate the recruits, since the recrui ts would be placed into the appropriate model, and the tank volume and number of occupants would be used in selection and separa ting the recruits. Data Collection The potential performance variables were collected by means of surveys, permits, and inspections. The use of surveys was e ssential for collecting the household activities variables, which were mailed to the particip ant. Most of the participants mailed the surveys back promptly but many of the partic ipants did not, leading to phone calls or having the participants complete the survey during an inspection. Monitoring solids accumulation was performed for one year in 6-month intervals. It is recommended to monitor systems for the entire pump-out interval after the septic tank is pumped. Having a longer interval betw een monitoring would allow enough time for more participants to be included. The ch anges in accumulation observed in this study lead to the recommendation that mon itoring intervals do not exceed 1 year.

PAGE 100

87 Calculation of Solids Accumulation and Model Development The calculation of solids accumulation is performed in several steps, tank dimension collection, volume calculation, and accumulation rate calculation. Selecting participants based on having known septic ta nk dimensions, if possible, would prevent the introduction of error incurred from cal culating tank dimensions. It is also recommended that the investigator s have or receive sufficient tr aining in statistics prior to the modeling phase to ensure that all consider ations have been made prior to and during analysis.

PAGE 101

88 APPENDIX A CONTENTS OF PACKAGE INITIALLY MAILED TO PARTICIPANTS The mailing campaign consisted of a flier, 2 consent forms, an initial survey, and a pamphlet. The 2 consent forms allowed the hom eowner to keep one for their records and return the other with the surve y. The initial survey is presen ted in Appendix B. The flier, consent form, and pamphlet are presented in this Appendix.

PAGE 102

89 University of Florida (UF) and Charlotte County Health Department (CCHD) Onsite Sewage Treatment and Disposal System (OSTDS) Study Brochure Prepared By The University of Florida Environmental Engineering Sciences Here is what we are requesting that you do: STEP 1: Read and sign the consent form: Read the form closely so you understand how this study can benefit you and Charlotte County. Sign the form in the signature box. STEP 2: Complete the Survey: Make sure to fill it out as accurately as you can! Mail the survey and consent form using the stamped, self-addressed envelope provided. STEP 3: Await contact from CCHD: If you choose to participate in this important study, personnel from the CCHD and Charlotte County Utilities (CCU) will be stopping by your house. Once your system has been determined ready for study, CCHD and CCU will install monitoring ports and risers in your tank and drainfield. They will then monitor your OSTDS or system levels twice a year. What will we be doing with all of this information? Measure solids over the course of the year: We will take the data that CCHD gathers when it monitors your tank twice during the year. Create a model: Using the data collected during monitoring and from your survey, we will create a model that will allow the prediction of performance and required pumping of any OSTDS. Use the model: From this model, we will be better able to guide OSTDS owners like you in more efficient practices that will result in lower repair costs for you and minimize the OSTDS public health risks and environmental impact on local water resources. We thank you for considering participating in this study. If you have any questions, please do not hesitate to contact Mr. Bob Vincent (CCHD) at (941)743-1266 or Dr. Angela Lindner (UF) at (352)846-3033 or at alind@eng.ufl.edu Figure A-1 Flier (a) front (b) back

PAGE 103

90 INFORMED CONSENT FORM Official Copy to be Returned with Survey Dear Septic Tank Owner: We are writing you to ask for your help in a study of septic tank systems. The study is a multi-year project to explore how maintenance and daily household activities can affect septic system performance. The ultimate goal of this project is to better able to assist you in properly maintaining your septic system. You are one of two hundred septic tank owners in Charlotte County who have been asked to participate in our study. This is a two-tiered study. First, we ask that you take approximately twenty minutes to complete the enclosed survey, and mail it back to us using the stamped, self-addressed envelope also enclosed in this package. The survey asks you questions about daily household activities and your household occupancy. Protecting the confidentiality of your answers is very important to us. We assure you that your survey responses will be kept strictly confidential to the extent provided by law, and the results will only be publicly reported in aggregate statistical format. There is an identification number on the survey for tracking purposes, so we know not to send you another survey. Upon completion of the survey, the second portion of the study involves monitoring your septic system for approximately one year. First, Charlotte County Health Department (CCHD) personnel will inspect your system. The CCHD personnel will identify any necessary repairs, which you will then need to have made at your expense. Next, CCHD p ersonnel will install a drainfield monitoring port, and Charlotte County Utilities p ersonnel will install a riser in your septic tank. Twice a year, CCHD personnel will monitor your septic tank levels. You must be at least 18 years of age to participate, and your participation is voluntary. We anticipate no risks to you. If you agree to participate in both portions of this project, you will receive a septic tank pumpout for a nominal fee of $15-20. We are especially grateful for your help because it is only by asking septic tank users like you to share information about their septic system that we can understand how septic tank maintenance and household practices can affect septic system performance. If you have any questions or concerns, please feel free to contact me. In addition, please feel free to contact the University of Florida’s Institutional Review Board at (352) 3920433 if you Figure A-2 Consent Form Page 1

PAGE 104

91 have any questions about your rights as a study participant. If you wish to participate in this program, please indicate by signing your name and placing today’s date in the space p rovided below. Please return this form, along with your completed survey, in the enclosed self-addressed envelope. Thank you in advance for your help with this important study. Sincerely yours, Angela S. Lindner, Ph.D. Environmental Engineering Sciences, University of Florida Figure A-3 Consent Form Page 2 _________________ _________________ ___ _______ ______________ Your Signature Today’s Date

PAGE 105

APPENDIX B INTIAL AND FOLLOWUP SURVEYS

PAGE 106

93 On-Site Sewage Treatment Disposal Survey Charlotte County Health Department* and The University of Florida Department of Environmental Engineering Sciences# *Port Charlotte, Florida 33948 #Gainesville, Florida 32611 Y our Name: _________________________________________________________ Phone number: HOME: (______)_____________________________ WORK: (______)_____________________________ Email address: _____________________________________ Mailing address: _____________________________________________________________________ _____________________________________________________________________ Physical address: (If different from above.) _____________________________________________________________________ _____________________________________________________________________ QUESTIONS CONCERNING OCCUPANCY IN YOUR HOME: 1. Number of years at current address: ______________________ 2. Number of people living in your home: _______________________ 3. Number of bedrooms in your home: _______________________ 4. Do you live here year round? (Circle One.) YES NO If no, number of months of the year you live here: _______________ QUESTIONS CONCERNING YOUR DAILY ACTIVITIES IN YOUR HOME THAT MAY AFFECT YOUR SEPTIC SYSTEM’S PERFORMANCE: 5. Has your yard ever flooded in the vicinity of the septic tank after rains? (Circle One.) YES NO 6. Do you have well water or city water ? (Circle One.) Figure B-1 Initial Survey Page 1

PAGE 107

94 If you answered city water what is your normal monthly usage?____________ If you answered city water do you irrigate the yard with this water? (Circle One.) YES NO If you answered well water, do you use water softener for your drinking water? (Circle One.) YES NO 7. Do you use a clothes washing machine in your house? (Circle One.) YES NO If yes, does the washing machine drain into the septic tank?________ 8. How many loads are washed in a week?_____ most loads in a day? _____ 9. Do you have and use an automatic dishwasher? (Circle One.) YES NO How many loads are washed in a week?______ In a day?______ 10. Do you have a garbage disposal? (Circle One.) YES NO If yes, how often do you use the disposal? (Circle One.) Don’t use Occasionally use Use after meals Always use 11. Do you have a (Circle one): Low-Flow Toilet YES NO Low-Flow Showerhead YES NO QUESTIONS CONCERNING YOUR SEPTIC SYSTEM: 12. What year was your home built? ______Has the septic system been replaced? ____ If it has been replaced, in what year was it replaced?______ 13. Do you know where your septic tank and drain field are located? (Circle One) YES NO 14. Does anyone park or drive on your drain field? (Circle One.) YES NO 15. Are there any plants planted on or near the drain field? (Circle One) YES NO 16. Have you ever had problems with your septic system? (Circle One.) YES NO If so, explain the problems and how it was corrected in the space provided below: ______________________________________________________________________ _ ______________________________________________________________________ Figure B-2 Initial Survey Page 2

PAGE 108

95 ________________________________________________________________________ 17. When was the last time your septic tank was pumped out? _______________________________________________________________________ 18. Is the septic tank or drainfield within 75 feet of surface water (lake, pond or other)? (Circle One.) YES NO If you responded YES, how far (in feet) is the water from the septic tank or drainfield:_________ 19. Check the following that you dispose of in your drains or toilets: paint thinner plastic items disinfectants bleach pesticides nylon products coffee grinds food grease feminine products medications cigarette filters paper towels disposable diapers rubber products any type of food item salad oil sour milk Comments: _____________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ (You may continue on the reverse side of this page if necessary.) 20. Further input by you will help researchers guide septic tank users like you in more efficient practices, resulting in lower repair costs and minimal environmental impact on local water bodies. Would you be willing to participate further in our study? (Circle One.) YES NO If so, what is the best means of contacting you? (Circle One.) Mail Email Phone If by phone, when is the best time of day to contact you? _______ Figure B-3 Initial Survey Page 3

PAGE 109

96 On-Site Sewage Treatment Disposal Follow Up Survey Charlotte County Health Department* and The University of Florida Department of Environmental Engineering Sciences# *Port Charlotte, Florida 33948 #Gainesville, Florida 32611 Name __________________________________ Participant ID #_______ Primary Phone Number: ____________________ home/work/mobile Secondary Phone Number: __________________ home/work/mobile Occupancy 1. Please indicate the number of people living in your home that fit in the following age ranges: ___ younger than 11 ___ 1119 ___ 20-60 ___older than 60 House 2. Number of bedrooms: ______ 3. Number of bathrooms: ______ 3a. How many of your toilets are: ______ Water saving toilets ______ Regular flow toilets 3b. How many of your showers have a: ______ Water saving showerhead ______ Regular showerhead Appliances 4. Please check the box that best describes your washing machine. No, I do not have a washing machine in my home. Go to question 5. 4a. What is your washing machine capacity? Compact (1.7 – 2.3 cubic feet) Medium (2.31 – 2.5 cubic feet) Large (2.51 – 3 cubic feet) Extra Large (>3.1 cubic feet) 4b. What is the loading location? Front Top 4c. Which detergent do you primarily use? Liquid Powder Both 4d. Do you use bleach? No Yes If yes, Number of loads per week _____ Amount of bleach _________ 4e. Do you use liquid fabric softener? No Yes 4f. How many loads of laundry are typically done each week?______ 5. Please check the box that best describes your dishwasher. No, I do not have a washing machine in my home. Go to question 6. 5a. What is the size of your dishwashe r? Standard Size (24 inches wide) Compact Size (18 inches wide) 5b. Which detergent do you primarily use? Liquid Powder Both 5c. How many dishwasher loads are typically done each week?___ Figure B-4 Follow-up Survey Page 1

PAGE 110

97 Household Habits 6. How many of the following meals are typically prepared in your home during the week: ____ Breakfast ____ Lunch ____ Dinner 6a. Do you scrape your plates off in to the garbage can after meals before rinsing them? No Yes 6b. When rinsing dishes in the sink, what do you do with the remaining food particles in strainer: let them go down the sink drain put them in the garbage can or other 7. How often do you fry foods during a month: _______ 7a. Do you pour used grease down the sink drain? No Yes 8. Do you use septic system additives for your system? No Yes If yes, 8a. Product Name:________________________ 8b. How often do you use it: Once every _______ Month(s) 9. Have your habits changed as a result of the educational material provided to you by the Department of Health? No Yes If yes, please indicate which habits ________________________________________________ _________________________________________ _________________________________________ Figure B-5 Follow-up Survey Page 2

PAGE 111

98 APPENDIX C DESCRIPTION OF METHOD USED TO DIVIDE PARTICIPANTS INTO PHASE 1 AND 2 GROUPING Variable information collected in the initia l survey was used to separate recruits into two similar samples and presented in this appendix. Frequency charts and statistical descriptions are presented for quantitativ e variables. The predicted and actual distributions of the variables for each phase are also presented. Variable Descriptions The descriptions of variables used to divide the recruits are presented for all of the recruits. Figure C-1, C-2, C-3, and C-4 are frequency charts of the quantitative variables. The range, mean, and median are also presente d for quantitative variables, Table C-1. 0 20 40 60 80 100 120 140 123456789101112 People/ homefrequency Figure C-1 Number of Occupant s per Home Frequency Chart

PAGE 112

99 0 50 100 150 200 250 123456789101112 months per yearFrequency Figure C-2 Occupancy in Home dur ing the Year Frequency Chart 0 5 10 15 20 25 30 35 40 45 012345678101112141516172028 loads per weekFrequency Figure C-3 Washing Machine Loads per Week Frequency Chart

PAGE 113

100 0 10 20 30 40 50 60 01234567910 loads per wkFrequency Figure C-4 Dishwasher loads per Week Frequency Chart Table C-1 Quantitative Data Description Variable CountLow range High range MeanMedianLow High Not available Occupants (capita) 238 1 12 2.6 2 149 89 0 Occupancy (mo./yr.) 238 3 12 11.6 12 19 219 0 Washing machine loads 238 0 28 5.2 4 121 117 0 Dishwasher loads 238 0 10 2.62 2 123 114 0 Phase Distribution The recruits were separated into two pha ses using the distribution of the high and low levels. The desired sample size of th e two samples was Phase 1 with 198 and Phase 2 with 40. The quantity of low and high levels for each phase was according to the distribution and sample size of each phase. Table C-2 shows the predicted quantity of low and high levels and the actual quantity of both levels afte r the recruits were

PAGE 114

101 separated. Qualitative variables used the hi gh level to signify yes and the low level to signify no. Table C-2 Variable Phase Distribution Phase 1 Phase 2 Predicted Actual Predicted Actual Variables LowHighLowHighLow High LowHigh Capita 124 74 125 73 25 15 24 16 Occupancy per year 16 182 17 181 3 37 2 38 Washing machine loads 101 97 103 95 20 20 18 20 Dishwasher loads 102 95 100 98 21 19 23 17 Flooding 180 18 179 19 36 4 37 3 Washing machine drains to septic 27 171 30 168 6 34 3 37 Water conserving toilets 105 91 105 90 21 18 21 19 Water conserving showers 105 91 83 111 21 18 14 26 System repair or replacement 81 114 181 10 16 23 38 2 System location Knowledge 8 188 7 190 2 38 3 37 Parking or driving on system 196 2 196 1 39 0 39 1 Plants on Drainfield 127 68 127 68 26 14 26 14 Systems within 75’ of surface water 182 14 184 12 37 3 35 5 Water SourceWell 169 29 171 27 34 6 32 8 Water Source-City 36 162 34 164 7 33 9 31 Water SourceBoth 191 7 191 7 39 1 39 1

PAGE 115

102 APPENDIX D TANK DIMENSIONS This appendix presents the tank dimens ions for the known manufacturers, tanks dimensions calculated with Method 1 and Method 2, and the relationship values used in Method 2. Manufactured Tank Dimensions Table D-1Manufactured Tank Dimensions Manufacturer Volume (gal) N w1 (in) w2 (in) w3 (in) l1 (in) l2 (in) l3 (in) h1 (in) h2 (in) h3 (in) T (in) V-bottom Taylor 750 1 45 43 23 93 92 91 6.5 35 13 3 Stans 750 33 44.5 39 21 92 88 87 8 35 16 3 Nokomis 750 2 51 46 29 98 95 94 9 32 19 3 Southern 750 8 45 42 22 93 93 93 8 34 13 3 Stan’s 900 60 45 40 22 111 107 106 8 35 16 Nokomis 900 6 55 47 28 110 107 106 9 33 18 3 Southern 900 26 43 40 22 110 110 110 8 34 15 3.5 Sebring 900 36 55.6 50 33 98 97 94 10 28 19 2 Taylor 950 4 42.5 40 22 110 108 108 7.3 34 16 2.5 Stan’s 1050 2 45 40 22 115 111 110 8 40 16 3 Southern 1050 4 48 40 22 121 121 121 8 36 15 3.5 Southern 1200 1 58 49 36 116 116 116 8 30 22 4 Sebring 1500 1 57 53 43 120 120 120 7 40 21 4 Taper Side Crews 900 1 53 47 113 106 9.5 40 10 2.5 Method 1 Tank Dimension Calculation Method 1 tank dimension calculations were used to determine the tank dimensions for septic tanks with less than a 600-gal lon volume. The dimensions calculated are presented in Table D-2 for each system. The calculations used in this method are listed below.

PAGE 116

103 1. Surface Area (in2) = (Tank Volume (gallons ) /Liquid Height (in))*231 2. Average Width (in) = square root (Surface Area (in2)/3) 3. Average Length (in) = 2*Average Width (in) 4. h1 = (0.15*Tank Volume (gallons) *231)/ Surface Area (in2) 5. Total Tank Height (in) = h1 (in) + HL (in) 6. w1 = Tank Lid Width (in) – 6 in 7. l1= Tank Lid Length (in) – 6 in 8. w3 = w1 – 4 9. l3 = l1 Table D-2 Method 1 Dimension calculations ID Volume Surface Area HL Avg. Width Avg. Length w1 w3 l1 l3 h1 2283 500 2333 49.5 34 68 41 37 81 81 7.4 2688 500 2264 51 33.6 67 32 28 72 72 7.65 2007 560 3058 42.3 40 80 35 31 73 73 6.3 2812 600 2665 52 36.5 73 38.5 34.5 73 73 7.8 2813 600 2917 47.5 38 76 40 36 76 76 7.1 Method 2 Tank Dimension Calculations Method 2 tank dimension calculations were used for septic tanks with a volume of 750 and 900 gallons. The calculation was based on f our relationships. The relationships were calculated for each tank volume (Table D-3). All dimensions that were calculated for each system are presented in Table D-4. The following calculations were used to determine the dimensions: 1. w1 =W-2t 2. l1 = L – 2t 3. h2 = R2 HL 4. h3 = (1-R2) HL 5. w2 = w1 – R3 (h1+h2) 6. w3 = w2/R1 7. l2 = L – R4* (h1+h2) 8. l3 = L – R4* (h1+h2+ h3) Table D-3 Method 2 Ratios and Dimensions Tank Volume R1 R2 R R h1 t 750 1.8 2.3 0.12 0.057 8.25 3 900 1.9 2.3 0.13 0.07 8.57 3

PAGE 117

104 Table D-4 Method 2 Calculated Dimensions ID Tank Volume (gal) Lid Length (in) Lid Width (in) HL (in) w1 (in) w2 (in) w3 (in) l1 (in) l2 (in) l3 (in) h1 (in) h2 (in) h3 (in) 1059 750 97 51 51 45 44 24 91 90 88 8.2 36 15 10 750 98 51 51 45 40 22 92 89 89 8.2 36 15 596 750 98 48 51 42 41 23 92 89 89 8.2 36 15 949 750 102 45 50 39 34 19 96 93 93 8.2 35 15 1924 750 99 50 51 44 39 21 92 89 89 8.2 35 16 2287 750 98 47 50 41 36 20 92 89 89 8.2 35 15 2779 750 97 49 50 43 38 21 91 88 88 8.2 35 15 2782 750 99 64 51 58 53 30 93 90 90 8.2 36 15 2795 750 99 48 49 42 37 21 93 91 89 8.2 34 15 2740 750 95 48 50 42 38 21 89 86 86 8.2 35 15 2870 750 101 50 48 44 39 22 95 93 92 8.2 34 15 2916 750 99 50 53 44 39 21 93 90 89 8.2 37 16 2822 750 90 48 52 42 36 21 90 87 87 8.2 36 16 2879 750 90 48 51 42 37 21 84 82 81 8.2 36 15 229 900 102 53 47 48 42 25 104 101 100 8.6 36 16 1905 900 99 53 49 47 41 24 93 90 89 8.6 34 15 2658 900 98 49 52 43 37 22 92 89 88 8.6 36 16 2679 900 99 53 46 47 42 25 93 90 89 8.6 32 14 2712 900 98 46 52 40 34 21 92 89 88 8.6 36 16 2736 900 99 53 51 47 41 24 93 90 89 8.6 35 15 2874 900 110 54 52 48 42 25 104 101 100 8.6 36 16 298 950 102 54 48 48 42 41 96 93 92 8.6 34 14

PAGE 118

105 LIST OF REFERENCES ASI AmeriSep, Inc. Septic Tank and Drai nfield Maintenance (www.amerisep.com) 9/29/99 Anderson, D. and R. Siegrist. 1989. The Performance of Ultra-Low-Volume Flush Toilets in Pheonix. Journal of the Amer ican Water Works Association 81(3):52-57. Ayres Associates, 1993. Onsite Sewage Disposal Research in Florida: An Evaluation of Current OSDS Practices in Florida. Tampa, Ayres Associ ates. HRS Contract No. LP-596 Ayres Associates. 1987. The Impact of Floridas Growth on the Use of Onsite Sewage Disposal Systems. Tampa, Ayres Associates. Barshied, R. and H. El-Baroudi. 1978. Phys ical-Chemical Treatment of Septic Tank Effluent. Journal of Water Polluti on Control Federation 46(10):2347-2354 Baumann, R. 1978. Septic Tanks. National Home Sewage Treatment Symposium. American Society of Agriculture Engineers. St. Joseph, MI. Bell, H. 1977. Reviving the Septic Tank. ASCE-Civil Engineering 47(12):83-84. Bicki, T. 1989. Septic Systems Operation a nd Maintenance of On-Site Sewage Disposal Systems. University of Illinois at Ur ban-Champaign, College of Agriculture, Cooperative Extension Service lw-15.il Benton County Environmental Health. 1998. Septic Systems: A Homeowners Guide to Operation and Maintenance. Corvallis, OR. www.co.benton.or.us/health/eh/guide.htm 5/21/03 Bounds, T. 1996. Septic Tank Septage Pumping Intervals. Orenco Systems, Inc., Sutherlin, Oregon. Bounds, T. 1992. Study Provides Formulas for De termining Septic Tank Pumping Intervals. National Small Flows Quarterly 6(4). Brown County, Wisconsin. 2003. County Codes of Ordinances. 11.073(c)(5)(a). www.co.brown.wi.us/County_Clerk/C ountyCode/Outline.html 5/21/03 Brown, R. 1998. Soils and Septic Systems. Fact sheet SL-118. Cooperative Extension Service. University of Florida, Gainesville, Florida.

PAGE 119

106 Brown, R. and Bicki, T. 1987. On-Site Sewa ge Disposal Importa nce of the Wet Season Water Table. Notes in Soil Science No. 30. Soil Water Science Department, University of Florida. Brown, R. and Bicki, T. 1985. On-Site Sewage Disposal Wastewater Flow and Quality. Notes in Soil Science No. 19. Soil Water Science Department, University of Florida. Brown, R. and Peart, R. 1996. Your Home Septic System. SL-59. Cooperative Extension Service. University of Florida, Gainesville, Florida. Campbell, N.A. 1996. Biology. Benjamin/Cummings Publis hing Company. Menlo Park, CA. Canter, L. and Knox, R. 1985. Evaluation of Septic Tank System Effects on Ground Water Quality. Lewis Publisher, Ada, MI. Crites, R. and Tchobanogloos, G. 1998. Small and Decentralized Wastewater Management Systems. McGrawHill, Inc. New York, 2. Eliasson, J.M.; Lenning, D.A.; and Wecker S.C. 2001. Critical Point Monitoring A NewFramework for Monitoring On-Site Wastewater Systems. Onsite Wastewater Treatment:Proceedings of the Ninth Na tional Symposium on Individual and Small Community Sewage Systems. American Society of Agricultural Engineers, St. Joseph, MI. Fan, C., Field, R., Pisano, W., Barsanti, J ., Joyce, J., and Sorenson, H. 2001. Sewer and Tank Flushing for Sediment, Corrosion, a nd Pollution Control. Journal of Water Resources Planning and Management 127(3): 194-201. Florida Department of Health. Statistics: New Installations (www.doh.state.fl.us/environment/OSTDS /statistics/NewIn stallations.htm) 10/15/03 Jones, D. and Yahner, J. 1992. Operating and Maintaining the Home Septic System. ID142. Cooperative Extension Serv ice. Purdue University. www.agcom.purdue.edu/AgCom/Pubs/ID/ID-142.html 5/21/03 Kahn, L.; Allen, B.; and Jones, J. The Septic System Owners Manual. California: Shelter Publications, 1999. Laak, R. 1980. Multichamber Septic Tanks. Journal of Environmental Engineering Division, ASCE, Vol. 106, No. EE3, Proceedings Paper 15472, 1980, p. 539-546 Laak, R. and Crates, F.J. 1978. Sewage Treat ment by a septic tank. P. 54-61 In Home Sewage Treatment. Proceeding Seco nd National Home Sewage Treatment Symposium. American Society of Agricu lture Engineers., St. Joseph, MI ISBN:0-916150-11-9.

PAGE 120

107 LaPointe, B. and M. Clark. 1992. Nutrient Inputs from the Watershed and Coastal Eutrophication in the Florida Keys. Estuaries 15(4):465-476. Lesikar, B. 1999a. On-site Wastewater Treatment Syst ems: Septic Tank/Soil Absorption Field. L-5227. Texas Agricultural Engineer ing Service. Texas A&M University System. Lesikar, B. 1999b. On-site Wastewater Treatment Systems: Conventional Septic Tank/Drainfield. L-5234. Texas Agricultural Engi neering Service. Texas A&M University System. Loudon, T. 2002. Frequently Asked Questions About Septic Systems. Agriculture Engineering Newsletter May/June. Agricult ure Engineering Department. Michigan State University. www.egr.msu.edu/ag e/aenewsletter/1_ma y_june_02/loudon.html 5/21/03. Mancl, K. 1984. Estimating Septic Tank Pumping Frequency. Journal of Environmental Engineering, 110 (1): 283-285. Moore, J.D. 2002. Septic Tank Pumping Frequency Project. Nova Scotia On-Site Wastewater Applied Research Program. Center for Water Resources Studies, Faculty of Engineering, Dalhousie University. 5/21/03 Robertson, W.; J. Cherry; and E. Sudic ky. 1991. Ground-water Contamination from Two Small Septic Systems on Sand Aqui fers. Groundwater 29 (1):82-92. Robillard, P. and Martin, K. 1990. Septic Tank Pumping. F-161. Agricultural and Biological Engineering Depart ment. Penn State University. http://user.pa.net/~stephens/Countryside Pumping/SepticTankPumping.pdf 5/21/03 Scalf, M.; Dunlap, W.; and Kreissl, J. 1977. Environmental Effects of Septic Tank Systems. U.S. EPA No. 600/3-77-096. Septic Resources and Information Online. Pumping Your Septic Tank. www.septicinfo.com/doc/display/41.html 5/21/03 Siegrist, R. 1983. Minimum-Fl ow: Plumbing Fixtures. Journal of American Water Works Association 75(7):342-348. State of Florida. 2000. Standard for Onsite Sewage Tr eatment and Disposal Systems. Florida Administrative Code, Department of Health. University of Wisconsin-Madison. 1978. Management of Small Wastewater Flows. EPA600/7-78-173. U.S. Environmental Protec tion Agency, Office of Research and Development, Municipal Environmental Re search Laboratory (MERL), Cincinnati, OH.

PAGE 121

108 U.S. Census Bureau (2003) American Housing Survey for the United States: 1999 Current Housing Reports, Series H150/99RV, United Stated Government Printing Office, Washington, D.C., 20222 U.S. Census Bureau (1997) American Housing Survey for the United States 1995 U.S. Department of Agriculture. 1982. Equip Tips: How to Operate and Maintain Septic Tanks/Soil-Absorption System. Forest Service, San Dimas, CA. Equipment Development Center. U.S. Department of Agriculture. 1984. Soil Survey of Charlotte County, Florida. Soil Conservation Service. U.S. Department of Health Education, Welfare, 1967. Manual of Septic-Tank Practice. Public Health Service Publication No. 526. U.S. EPA 2002. Onsite Wast ewater Treatment Systems Manual. Office of Water. EPA/625/R-00/008. U.S. EPA. 2000a. Decentralized Systems Technology Fact Sheet: Septic System. Tank Office of Water EPA 832-F-00-040. U.S. EPA. 2000b. EPA Guidelines for Management of Onsite/Decentralized Systems. EPA 832-F-00-012. U.S. EPA. 1999. Decentralized Systems Technology Fact Sheet: Septic Tank-Soil Adsorption System. Office of Water, EPA/932-F-99-075. U.S. EPA. 1996a. National Water Quality Inventory: 1996 Report to Congress. [305b Report] EPA 841-R-97-008. www.epa.gov/ 305b/96report/index.html 5/21/03 U.S. EPA. 1996b. Clean Water Needs Survey Report to Congress. U.S. EPA. 1995. Clean Water Through Conservation. EPA 841-B-95-002. U.S. Environmental Protection Agency. O ffice of Water, Washington, D.C. 5/21/03 U.S. EPA. 1994. Guide to Septage Treatment and Disposal. Office of Science, Planning, and Regulatory Evaluation. Cincinnati, OH. U.S. EPA. 1980. Design Manual: Onsite Wast ewater Treatment and Disposal Systems. EPA Office of Water. EPA 625/180-01. Vincent, R. 1989. Memorandum to Pete Ev erett. “Comp Plan Hearing,” May 28, 1998.

PAGE 122

109 Vogel, M. 2001. Septic Tank Inspec tion and Trouble-Shooting. MontGuide Fact Sheet #9403. Montana University Extension Se rvice. Mantana State University. 1/2/02 Vogel, M. and Rupp, G. 1999. Septic Tank and Drainfield Operation and Maintenance. MontGuide MT 9401. Montana University Extension Service. Montana State University. www.montana.edu/wwwpb/pubs/mt9401.html 10/15/03 Washington Department of Health. 1994. On-s ite sewage system regulations. Chapter 246-272, Washington Administrative Code, adopted March 9, 1994, effective 1, 1995. Washington Department of Health, Olympia, WA. www.doh.wa.gov/ehp/ts/osreg1.doc 6/2/03 Weibel, S.; Bendixen, T.; and Coulter, J. 1949. Studies on Household Sewage Disposal Systems, Part I. U.S. Public Health Service Publication No. 397. Weiskel, P. and B. Howes. 1992. Differentia l Transport of Sewage Derived Nitrogen and Phosphorus through Coastal Watershed. Environmental Science and Technology 26: 352-360. Wilhelm, S.R.; Schiff, S.; and Cherry, J. 1994. Biogeochemical Evolution of Domestic Wastewater in Septic Systems: 1. C onceptual Model. Groundwater 32(6): 905-916. Wilcox, K. 1992. Glide audit takes a scientific look at septic tank pumping. National Small Flows Quarterly 6(4). Yates, R. 1985. Septic Tank Density a nd Ground-Water Contamination. Groundwater 23(5): 586-591.

PAGE 123

110 BIOGRAPHICAL SKETCH I was born and raised in Charlotte Count y, Florida, in 1978 to Susan Peters and Daniel Lurtz. After leaving Charlotte High School in 1996, I continued my education at Edison Community College in Punta Gorda, wher e I earned my Associate of Science in 1998. I transferred to the Univ ersity of Florida and earned my Bachelor of Science from the College of Engineering in the Environm ental Engineering Sciences Department in 2001. I stayed in the Environmental Engineer ing Science Department for my Master of Engineering degree to work on a project that was based out of my hometown. During my work on my masters degree, I married th e love of my life, Mr. Erik Lee Howard.


Permanent Link: http://ufdc.ufl.edu/UFE0002660/00001

Material Information

Title: Solids Accululation Rates for Onsite Sewage Treatment and Disposal Systems: A Focus on Charlotte County, Florida
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0002660:00001

Permanent Link: http://ufdc.ufl.edu/UFE0002660/00001

Material Information

Title: Solids Accululation Rates for Onsite Sewage Treatment and Disposal Systems: A Focus on Charlotte County, Florida
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0002660:00001


This item has the following downloads:


Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
    List of Tables
        Page viii
        Page ix
    List of Figures
        Page x
        Page xi
    Abstract
        Page xii
        Page xiii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Review of literature
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    Methods
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
    Results and discussion
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
    Summary and conclusions
        Page 80
        Page 81
        Page 82
        Page 83
    Recommendations for future work
        Page 84
        Page 85
        Page 86
        Page 87
    Appendices
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
    References
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
    Biographical sketch
        Page 110
Full Text












SOLIDS ACCUMULATION RATES FOR ONSITE SEWAGE TREATMENT AND
DISPOSAL SYSTEMS: A FOCUS ON CHARLOTTE COUNTY, FLORIDA














By

TRISHA LURTZ HOWARD


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA


2003

































Copyright 2003

by

Trisha Lurtz Howard



























This document is dedicated to the Lord Jesus Christ, my Lord and Savior, who brought
me through my weakness with his perfect love. And this document is also dedicated to
my loving husband.















ACKNOWLEDGMENTS

I would like to thank to the Charlotte County Department of Health, the Florida

Department of Environmental Protection, and the United States Environmental Protection

Agency for the opportunity to work on this project. I would also like to thank Dr.

Alexandre Trinidad in the Department of Statistics and Dr. Yong-Song Joo from IFAS

Statistics for their willingness to volunteer their time, and Dr. Gary Stevens from the

BCL for running the statistical analysis of the data. I am grateful to Mr. Paul Booher

from the FDOH for the information on tank manufacturers and schematic information.

This study would not have been possible without the willingness and cooperation

of the residents in Charlotte County to allow us to study their systems and provide their

household practices information. Finally, I wish to give thanks to Mr. Robert Vincent,

Mr. Bud Wimer, and Mr. Jeffrey Tompkins for their vigilance and guidance throughout

this project.

Most of all I would like to thank my family and friends. I would like to give a

special thank you to my brother-in-law, Thomas, and my dear friend, Liz, who helped me

through the trials of writing. And, of course, I would like to thank my parents for

preparing me for college and my husband for loving me through this research.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S ................................................................................................. iv

LIST OF TABLES .......................................... viii

LIST OF FIGU RE S .............. .......................... ........................ .. .. .... .x

ABSTRACT ................................................... ................. xii

CHAPTER

1 IN T R O D U C T IO N .................................................. .. .......................................... 1.....

A Case for Standardized Management of OSTDSs ................................................2...
E evidence of F ailure... ................................................................... .. .......... ... 2
Failure Reasons ................................. ................... ..... .. .... .... ................ .4
System Failure Impacts on Surrounding Area.................................................5...
C harlotte C county, F lorida .................................................................... ...............6...
R e search S co p e ..................................................................................................... 9

2 REV IEW O F LITER A TU RE ................................................................................ 11

O STD S D esign and O peration...................................... ...................... .................. 11
Septic Tank D esign and Operation.................. .............................................. 11
Septic tank design .......................................... ............. .... .. .............. 11
Septic tank operation ..................................... .. ........ ............ .. ............ 14
D rainfield D esign and O peration.................................................... ................ 16
D rainfi eld design ....................................... .. ....................... . ........... 17
D rainfi eld operation ...................................... ....................... .............. 18
O STD S M maintenance .... .. ................................. ............................ ............. 20
A annual Inspection ... ................................................................... .... ........... 2 1
M maintenance P um ping ......................................... ........................ .................. 2 1
EPA Management Guidelines ................... ................22
Previous Solids Accumulation Rate Research....................................... ................ 23
D discussion of Prior Studies .......................... ............................................ 23
U united States Public H health Service ................ ................................... 23
B ounds Study ......................................................................................... 26
M oore Study ..................................................................... . ........... 28
Com prison of Pum p Out Frequencies........................................... ................ 29


v









3 M E T H O D S ................................................................................................................. 3 2

O b j e c tiv e s ................ .......... ....................................................................................3 2
Task 1: Identification of Relevant Variables.........................................................33
W astew ater C characteristics ............................................................ ................ 33
S y ste m D e sig n .....................................................................................................3 5
Surrounding Environm ent .................................. ... ................ 35
Task 2: Selection and Recruitment of Participants................................................36
Subtask 2A : Participant Selection .................................................. ................ 37
Location of systems in Charlotte County................................................37
Identification of OSTDS density by soil type.........................................37
Random selection of potential participants .............................................37
Subtask 2B : R recruiting of Participants........................................... ................ 38
N ew sp ap er article ........................................ .. ..................... ..... .......... 3 8
M ailing cam paign ....................................... .. ..................... ... ........ .... 38
C county fair................................... ................... .................. 40
Subtask 2C: Division of Recruits into Phase 1 and Phase 2 of the Study ...........40
Subtask 2D: Data Collection and Databasing ................................................41
Initial survey ................................................................... . ........... 4 1
Follow -up survey......................................................................... ........... 42
Perm it inform ation .............. ............ .............................................. 42
Inspection inform action ......................................................... 42
H eight m easurem ents .............................................................. ................ 43
D atabasing of all variables collected....................................... ................ 43
Task 3: Calculation of Solids Accumulation........................................................ 43
Subtask 3A: Determination of Tank Dimensions...........................................44
Subtask 3B: Calculation of Solids Volumes in Each Tank ...............................46
Subtask 3C: Calculation of Accumulation Rates ...........................................48
Subtask 3D: Assessment of Trends in Accumulation ....................................48
Task 4: Interpretation of Phase I and Phase II Model Results...............................49
Subtask 4A : A ssess Sam ple Size.................................................... ................ 49
Subtask 4B: Assessment of Correlations ................ ....................................50
Subtask 4C: Assessment of Model Results ....................................................50

4 RE SU LTS AN D D ISCU SSION ............................................................ ................ 52

Task 1: Identification of Relevant Variables........................................................ 52
Task 2: Selection and Recruitment of Participants ...............................................55
Subtask 2A: Selection of Potential Participants............................................ 55
Subtask 2B : R ecruit Participants .......................................... ......................... 56
Subtask 2C: Separation of Recruits into Phase 1 and 2..................................59
Subtask 2D: Data Collection and Databasing ...............................................60
Task 3: Calculation of Solids Accumulation........................................................ 62
Subtask 3A: Calculation of Tank Dimensions ...............................................62
Subtask 3B: Calculation of Solid Volumes Septic Tank................................62
Subtask 3C: Calculation of Accumulation Rates ...........................................63
A ccum ulation rate per system ................................................. ................ 64









A ccum ulation rate per person ................................................. ................ 65
Subtask 3D : Trends in A ccum ulation............................................. ................ 66
Accumulation trends during the first year............................... ................ 66
Accumulation trends in relation to people and septic tank volume .............67
Task 4: Interpretation of Phase 1 and Phase 2 Model Results...............................71
Subtask 4A : A ssess Sam ple Size.................................................... ................ 71
Subtask 4B : D evelopm ent of Correlations..................................... ................ 74
Sludge accum ulation rate correlations .................................... ................ 74
Scum accum ulation rate correlations ...................................... ................ 75
Subtask 4C: Development of M odel Results.................................. ................ 77

5 SUM M ARY AND CONCLU SION S.................................................... ................ 80

6 RECOMMENDATIONS FOR FUTURE WORK .......................... ..................... 84

Identification of R elevant V ariables ...................... .......................... ..................... 84
Selection, Recruitment, and Monitoring of Participants ................. ..................... 85
P participant Selection .............................................. ....................... .... ......... 85
R recruiting P participants ........................................ ........................ ................ 85
D division of Recruits for Tw o Groups............................................. ................ 86
Data Collection ..................... ..... .................................. .. . .. ............... 86
Calculation of Solids Accumulation and Model Development ............................... 87

APPENDIX


A CONTENTS OF PACKAGE INITIALLY MAILED TO PARTICIPANTS ............88

B INTIAL AND FOLLOW UP SURVEYS ........................................ ..................... 92

C DESCRIPTION OF METHOD USED TO DIVIDE PARTICIPANTS INTO
PH A SE 1 A N D 2 GR OU PIN G ..................................... ..................... ................ 98

D TAN K D IM EN SION S ................................................................... ............... 102

M manufactured Tank Dimensions...... ......... ......... ..................... 102
Method 1 Tank Dimension Calculation...... .... ........................ 102
Method 2 Tank Dimension Calculations ............... ....................... 103


LIST O F R EFEREN CE S .. .................................................................... ............... 105

BIO GRAPH ICAL SK ETCH .................. .............................................................1...... 10















LIST OF TABLES


Table page

2-1 R residential Estim ated Sew age Flow ................................................. ................ 14

2-2 M minimum Effective Septic Tank Capacities ....................................... ................ 14

2-3 USPHS Septic Tank Years of Service (Weibel et al., 1949)...............................24

2-4 USPHS Accumulation Means and Medians (Weibel et al., 1949)........................24

2-5 Total per Capita Sludge and Scum Accumulation (Weibel et al., 1949) ..............26

2-6 Moore Study (2002) Distribution of Years of Service........................................28

2-7 Moore Study (2002) Scum and Sludge Accumulation Trends ..............................29

2-8 Sum m aries of Prior Studies....................................... ....................... ................ 30

4-1 Potential Performance Factors Describing Wastewater Quality and Hydraulics..... 54

4-2 Potential Performance Factors Describing System Design and Condition.............. 55

4-3 Potential Performance Factors Describing Surrounding Environment................. 55

4-4 "Most Populated" Soils (with Largest Number of OSTDSs) in Charlotte County..56

4-5 R ecruitm ent R results .............. ............... .............................................. 58

4-6 Distribution for Quantitative of Household Characteristic for All Recruits............60

4-7 Distribution for Qualitative of Household Characteristics for All Recruits ..........60

4-8 Frequencies for Each Level of Household Characteristics for Each Phase ............61

4-9 Scum Volume 6 and 12 Months After Pump out................................................63

4-10 Sludge Volume 6 and 12 Months After Pump out..............................................63

4-11 Total Solids Volume 6 and 12 Months After Pump out......................................63

4-12 Scum A ccum ulation R ates ........................................ ....................... ................ 64









4-13 Sludge A ccum ulation R ates ....................................... ...................... ................ 64

4-14 Total Solids A ccum ulation R ates........................................................ ................ 64

4-15 Scum and Sludge Accumulation Rate Data Determined Using Linear Fits ............65

4-16 Scum per Person A ccum ulation Rate.................................................. ................ 65

4-17 Sludge per Person A ccum ulation Rate................................................ ................ 65

4-18 Total Solids per Person Accumulation Rate ............... ................................... 65

4-19 Accumulation Rates of Solids per Person Determined Using Linear Fits ............66

4-20 Solids Volume Change from 6 months to 12 months .........................................66

4-21 Solids Accumulation Rate Change from 6 months to 12 months .........................67

4-22 Accumulation Rates Based on the Number of People in the Home......................68

4-23 Accumulation Rate Based on Septic Tank Volume...........................................69

4-24 Accumulation Rate based on Septic Tank Capacity ........................... ................ 71

4-25 Significant Sam ple Size V alues .......................................................... ................ 73

C-1 Quantitative Data Description...... ............. ............ ..................... 100

C-2 V variable Phase D distribution ........................................................ 101

D-1 M manufactured Tank Dimensions ....... ........ ........ ..................... 102

D-2 M ethod 1 Dimension Calculations...... ........ ...... ...................... 103

D-3 M ethod 2 Ratios and Dimensions ....... ......... ........ ...................... 103

D-4 M ethod 2 Calculated Dimensions ....... ......... ........ ...................... 104















LIST OF FIGURES


Figure page

1-1 OSTD S Locations in Charlotte County.....................................................7...

1-2 Average Number of New Systems Installed from 1971 to 2001 .............. ...............8

2-1 A M multiple Chamber Septic Tank Schematic...................................... ............... 13

2-2 Septic Tank Width Profiles (a) V-bottom (b) Taper .......................................... 13

2-3 PHS Rate of Scum & Sludge Accumulation....................................... ................ 25

2-4 Bounds Study Volume of Total Solids For Eight Years .....................................27

3-1 Selected Systems in Mid-County 2 Basin per Soil Type ....................................39

3-2 V-bottom Septic Tank Schematic with Dimensions ...........................................45

3-3 Taper-Side Septic Tank Schematic with Dimensions.........................................45

3-4 Height Dimensions for Liquid Height (HL), Scum Height (hs), and Sludge ..........47

4-1 Divisions of Performance Variables into the Three Characteristic Groups .............53

4-2 Selected Homes having OSTDSs within Mid-County-2.....................................57

4-3 Accumulation Rate Trends Based on Number of People in the Home .................69

4-4 Accumulation Rate Trends Based on Septic Tank Volume................................70

4-5 Accumulation Rate Trends Based on Septic Tank Capacity...............................72

4-6 Scatter Plots for Sludge Accumulation Rates at 6 Months .................................78

4-7 Scatter Plots for Scum Accumulation Rates at 12 Months .................................79

A -i F lier (a) front (b) back ...................................................................... ................ 89

A -2 C onsent F orm P age 1 ...................................................................... ................ 90

A -3 C onsent F orm P age 2 .. ..................................................................... ................ 91









B -I Initial Survey Page 1 ............. ................ ................................................. 93

B -2 Initial Survey P age 2 .. ...................................................................... ................ 94

B -3 Initial Survey P age 3 .. ...................................................................... ................ 95

B -4 F ollow -up Survey P age 1 ......................................... ........................ ................ 96

B -5 F ollow -up Survey P age 2 ......................................... ........................ ................ 97

C-i Number of Occupants per Home Frequency Chart.............................................98

C-2 Occupancy in Home during the Year Frequency Chart ......................................99

C-3 Washing Machine Loads per Week Frequency Chart.........................................99

C-4 Dishwasher loads per Week Frequency Chart ....... ......................................100
















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

SOLIDS ACCUMULATION RATES FOR ONSITE SEWAGE TREATMENT AND
DISPOSAL SYSTEMS: A FOCUS ON CHARLOTTE COUNTY, FLORIDA

By

Trisha Lurtz Howard

December 2003

Chair: Angela S. Lindner
Major Department: Environmental Engineering Sciences

In 1999, 24.1% of American households and more than 60 million people used

onsite sewage treatment and disposal systems (OSTDSs) for domestic wastewater

treatment, with Florida consistently containing the largest number of systems than any

other state. For example, in 1990, Florida was reported as havingl.56 million OSTDSs.

In Charlotte County, Florida, approximately 24,000 systems were installed before 1983,

and, as of 1998, nearly 40,000 systems were in place, with 82% of these in residential

areas.

As these systems age, they may eventually fail if not maintained. A survey

conducted by the U.S. Census Bureau (1997) estimated that 403,000 homes experienced

system failure within the 3-month survey period, and 31,000 of these homes were

reported to have four or more breakdowns during this period. Studies reviewed by the

U.S. Environmental Protection Agency (U.S. EPA) cite failure rates ranging from 10-









20%. System failure surveys typically do not include systems that might be

contaminating their surrounding environment, as these failures are not always obvious.

The primary goal of this study was to better understand the underlying factors

(social, geographical, system design, etc.) that impact system performance. The ultimate

goal of this study was to provide CCDOH with a list of factors that potentially hamper

the ability of the region's OSTDSs to perform effectively. The primary methods to

determine these factors involved a combination of recruiting for participants, data

gathering using surveys, inspections, and permits, and multiple linear regression (MLR)

analysis. Two hundred twenty-one Charlotte County residents were recruited for

participation in this study. MLR analysis related solids accumulation rates (as dependent

variables) with the performance variables collected in the data gathering phases.

Those performance variables that were identified as having the greatest impact on

solids accumulation were related to wastewater generating activities in the household and

flooding frequencies. The scum accumulation rate significantly related to the use of

garbage disposals, the disposal of food particles while rinsing dishes, the washing

machine capacity, and the dishwasher detergent. The sample size was limited in yielding

significant results for the sludge accumulation rate.

Despite the inability of constructing statistically robust multiple linear correlations,

this study yielded a greater understanding of the importance of adopting better household

practices that result in less potential for OSTDS failure. By establishing community

outreach programs for OSTDS owners, CCDOH can prevent risk to the environment and

public health by ensuring that Charlotte County's systems do not fail and intrude on

surrounding surface waters.














CHAPTER 1
INTRODUCTION

Results from the U.S. Census in the past 20 years indicate that use of onsite sewage

treatment and disposal systems (OSTDSs) is a common method of managing household

wastewater in the United States. In 1999, approximately twenty-three percent

(26,051,000) of all of the nation's homes used OSTDSs (U.S. Census Bureau, 2003),

including one-third of newly constructed homes and one-half of all mobile homes. Over

50% of OSTDSs in the United States were found to exceed 30 years of service,

surpassing the intended 20-30 years of useful life of these systems. Florida possesses the

largest number of OSTDSs than any other state in nation with 1.56 million in 1999 (U.S.

Census Bureau, 2003). In 1987, Florida exceeded 60,000 permits for new systems

annually (Ayres Associates, 1987). As the population in Florida increases along with the

number of households using OSTDSs for wastewater management, there is an urgent

need to address factors that affect the performance of these systems in order to minimize

and ultimately prevent negative public and environmental health impacts.

This report focuses on the results of a study, funded by the Charlotte County

Department of Health (CCDOH), that began in July 2001. The overall goal of this work

was to identify the most significant human and environmental factors that have potential

to cause an OSTDS to fail, and, with these results, to allow CCDOH to recommend best

management practices to its residents. Chapter 1 of this report provides an overview of

this project with a description of Charlotte County and the research scope. Chapter 2

presents a thorough literature review of all research to date concerning OSTDSs,









including detailed descriptions of their design, normal maintenance, and wastewater

characteristics. Chapter 3 presents the methods used in this study, and Chapter 4 presents

the results of this work. Chapter 5 presents the conclusion of this study, and Chapter 6

presents recommendations for best practices in OSTDS management and for extending

this study.

A Case for Standardized Management of OSTDSs

Homeowners typically have the sole responsibility for managing and maintaining

OSTDSs (U.S. EPA, 2002; Laak and Crates, 1978). During a 3-month period in 1995,

1.57% of the total systems in the nation experienced system failures, with 31,000 of those

homes reporting four or more OSTDS failures during that same period (U.S. Census

Bureau, 1997). During a 3-month period in 1999, 1.44% of the total systems in the

nation experienced system failures, with 27,000 of those homes reporting four or more

OSTDS failures during that same period (U.S. EPA, 2002). Despite an increase of

systems, the number of reported failures decreased from 1995 to 1999, possibly

indicating improved management of the systems. The OSTDS failure rate throughout the

U.S. ranges from 10-20% of all systems (U.S. EPA, 2000a).

Evidence of Failure

An OSTDS is considered to have failed when it no longer treats wastewater to

dischargeable conditions. Monitoring for system failure is often difficult because both

wastewater treatment and discharge occur underground. A wide variety of criteria exist

to signal system failure, and a brief description of these failure characteristics is presented

below.

Class I. The first type of failure symptoms, known as Class I, is the reentry of raw

sewage back into the house, commonly termed a "sewage backup" and immediately









noticed by the homeowner (Brown, 1998). The raw sewage returns through the drains or

toilets (Vogel and Rupp, 1999; Brown, 1998) from either blockage in the pipes

connecting to the septic tank or the septic tank approaching full capacity for solid storage.

A slow flushing toilet or emptying drain can be the first signs of a blockage in the pipes

or a near-full septic tank (Vogel and Rupp, 1999).

Class II. The second group of failure symptoms, called Class II, is raw or partially

treated sewage surfacing in the yard (Brown, 1998). In this class of failure symptoms,

the toilet and other water-using facilities usually function properly, but untreated or

poorly treated sewage surfaces in the yard or seeps along the surface of the ground near

the system (Vogel and Rupp, 1999; Brown, 1998). Evidence of a system failure for class

of symptoms is apparent when lush green grass flourishes over the system despite no

sewage surfacing. Excessive growth of plant materials indicates an excessive amount of

nutrient-rich liquid moving up through the soil (Vogel and Rupp, 1999).

Class III. The third type of failure characteristics, called Class III, is the decline in

water quality while the household plumbing and drainfield seem to be working perfectly

without evident odors or excess wetness around the drainfield (Brown, 1998). Failures of

this type result in a decline in the quality of groundwater and/or surface water; however,

because there is no other obvious evidence, homeowners may be skeptical that this is a

result of their systems (Brown, 1998). The build up of aquatic weeds or algae in lakes or

ponds adjacent to a homeowner's system is indication of nutrient overload from failing

OSTDSs (Vogel and Rupp, 1999).

Class IV. The final evidence of failures is a long-term, gradual environmental

degradation (Brown, 1998). There is little, if any, scientific evidence that ground water









or surface water is being degraded at a rate likely to be a problem for the current or next

generation of residents. However, modeling and long-term monitoring indicate that very

gradual environmental degradation may result from improper septic system practices at a

particular home site, in a neighborhood, or in a region. Of all the classes of system

failure, this one is the most difficult to prove (Brown, 1998).

Failure Reasons

Failing systems are often left unnoticed until Class I-IV evidence of failure (as

previously described) becomes bothersome to the homeowner or apparent to the

regulatory agency. System failures are typically the consequence of several factors, but

the most common reason is system mismanagement. OSTDS failures can be grouped

into three possible causes: the system location, the system design and condition, or

management of the system by the homeowner.

The system location can jeopardize the performance of an OSTDS depending on

the OSTDS density in the region, the presence of effective drainage, and elevation of the

seasonal high groundwater table. A high density of OSTDSs decrease the soil's natural

capacity to purify wastewater (Yates, 1985), while effective drainage (via permeable

subsoils) is critical to prevent liquids from entering the septic tank from a flooded

drainfield or leaky tank (Vogel and Rupp, 1999; Brown, 1998; Bounds, 1996; Bell,

1977). High groundwater elevation results in an insufficient unsaturated soil depth under

the drainfield, which must be maintained when the groundwater elevation is at its highest

elevation (Brownand Bicki, 1987).

System deterioration and under-design can also prevent proper functioning.

System failures can be minimized through informed planning and installation of the

system (Brown, 1998). Deterioration of a system is caused by root growth in pipes,









crushed drainfield pipes, poor original design, or poor installation. Septic tanks, suffering

from corrosion or root infiltration, allow water outside of the system to enter, and the

resulting hydraulic overload of the tank causes sewage to return to the home or to

surfaces in the nearby yard (U.S. EPA, 1980).

The daily habits of the occupants, such as water use and disposal activities, can

cause a system with proper siting and excellent condition to fail. Management of an

OSTDS, including use and maintenance practices, is the sole responsibility of the owner.

Therefore, for an owner to avoid the most commonly reported failure, hydraulic

overloading, he/she must routinely perform tasks, such as monitoring tank residual

buildup, scheduling pumping, ensuring proper flow distribution, checking pumps and

float switches, inspecting filtration media for clogging, and performing monitoring and

maintenance tasks (U.S. EPA, 2002). Unfortunately, most homeowners have a limited

knowledge of OSTDS management practices, thus increasing the risk of their system to

reach overcapacity and, ultimately, leading to clogged drainfields (U.S. EPA, 2000a;

Vogel and Rupp, 1999; Bell, 1977).

System Failure Impacts on Surrounding Area

OSTDS failures can result in endangering public and environmental health, not to

mention high costs for system repairs. Improper maintenance can yield undesirable

odors, mosquito breeding areas, repair or replacement, condemnation of residence,

groundwater contamination, and the spreads of disease associated with sewage (Bicki,

1989). Failed systems, mostly caused by improper maintenance, are the third most

common source of groundwater contamination (Robertson et al., 1991; Canter and Knox,

1985; Yates, 1985), and sewage has been attributed to being the source of nearly one

third of the miles of contamination observed along the U.S. ocean shoreline (U.S. EPA,









1996a; LaPointe and Clark, 1992; Weiskel and Howes, 1992). In 1996, the Clean Water

Needs Survey revealed that more than 500 communities in the nation have public health

problems caused by failed systems (U.S. EPA, 1996b). Over half of the waterborne

disease outbreaks in the nation are from consuming contaminated groundwater. The

contaminated groundwater is most frequently contaminated with OSTDS effluents

(Yates, 1985).

Charlotte County, Florida

Charlotte County was the subject of this study. Located approximately 100 miles

south of Tampa on the southwest coast of Florida, Charlotte County is 894 square miles in

area with the Gulf of Mexico serving as its west border. 705 square miles of Charlotte

County is land and the rest is water. In the 1960's and 1970's, 68 square miles were

subdivided into several hundred thousand 1/-acre lots. The maximum elevation of the land

is 35 feet above sea level, approximately 13 miles inland from the Charlotte Harbor, the

second largest estuarine harbor in Florida (also in Charlotte County). The county has over

300 miles of navigable and drainage canals with nearly 300,000 waterfront lots. The build-

able areas, developed and undeveloped, have a seasonal high groundwater table within

one inch of the ground surface. Figure 1-1 illustrates the location of homes served by

OSTDSs and sewer within Charlotte County.

As of 1998, just fewer than 40,000 OSTDSs existed in Charlotte County with 82%

residential and 18% commercial or institutional and in industrial zones. Approximately

24,000 systems were installed before 1983. The median age of systems in 1998 was 12

years. Charlotte County experienced rapid growth between the years of 1977 and 1990

with the peak of installations in 1978.


















Wastewater Treatment and Disposal Evaluation


Dmi> SoUrC C"harfivo C ly 61S DrXpar-movI ;and

Households on Mp hnrr Tr Lz l
Map Cri, r Tr 'i;s L 4arrI 2W 2


- I


C 3


12 eis
12' ^


Figure 1-1 OSTDS Locations in Charlotte County









2500
C',

0
7 2000

o 0 1500

0 1000





1970 1975 1980 1985 1990 1995 2000 2005

Year
Figure 1-2 Average Number of New Systems Installed from 1971 to 2001 in Charlotte
County (Florida Department of Health, 2003)

Charlotte County has eleven major municipal wastewater treatment plants

(MWWTP), all permitted at or above 50,000 GPD and 2 larger MWWTP permitted

above 2 MGD. The county also has 36 smaller MWWTP with a loading capacity of

50,000 to 75,000 GPD. The high count of OSTDSs used in the county is because of a

lack of existing infrastructure (Vincent, 1998).

In the mid-1990s, the Charlotte County Commission was prepared to begin a utility

expansion to connect most of Port Charlotte to sewer. The residents opposed the

expansion mainly because of the anticipated cost and the lack of evidence that the

OSTDSs were a source of pollution in the county. The cost of the expansion is $8,000

per property expected to be paid by the property owner, not including the monthly water

bill. With one-third of the population over 65 and one of the highest median ages of 58,

the community of Charlotte County attracts citizens for its excellent retirement lifestyle.

In 1999, there were 140,000 year-round residents and 60,000 winter residents visiting 4-6









months a year. The median income is $42,000 a year, and the median home price is

$74,000.

Research Scope

This project sought a novel approach to the study of OSTDSs in Charlotte County -

by better understanding the underlying factors (social, geographical, system design, etc.)

that impact system performance, a predictive model could be developed to enable

prevention of problems leading to system failures. The objective of this research by the

University of Florida was to determine the underlying factors that correlate with sludge

and scum accumulation and to develop, if possible, an accumulation model of sludge,

scum, and total solids using data measured during one year of service. The specific tasks

of this project are the following:

1. Identify relevant variables that may impact OSTDS performance.

2. Collect specific information concerning relevant performance variables from a
selected population of Charlotte County OSTDS owners.

3. Create a model to predict accumulation that will aid in the creation of a pump out
schedule specific to the individual OSTDS.

4. Interpret the model results that will, in turn, allow CCDOH to establish
recommended best management practices for OSTDSs.

The United States Environmental Protection Agency (U.S. EPA), Florida

Department of Environmental Protection (FDEP), and the Charlotte County Department

of Health (CCDOH) sponsored this research. More specifically, this project was funded

in part by a Section 319 Nonpoint Source Management Program Implementation grant

from the U.S. EPA through an agreement/contract with the Nonpoint Source

Management Section of FDEP.






10


By completion of these tasks, performance factors that influence solids

accumulation during the first year of service of an OSTDS were identified and best

management practices determined, thus aiding in preventing further environmental

deterioration caused by these systems and adding to the continuously growing body of

knowledge on trends in solids accumulation and required pumping frequencies.














CHAPTER 2
REVIEW OF LITERATURE

OSTDS Design and Operation

OSTDSs provide effective wastewater treatment when properly sited, designed, and

managed. A conventional OSTDS consists of a septic tank and a drainfield. An OSTDS

has many advantages over a wastewater treatment plant. OSTDSs require minimum

energy and technology, while also being low in cost. Unlike a wastewater treatment

plant, an OSTDS requires no operators, no moving parts, little scheduled maintenance,

and produces less sludge (Laak and Crates, 1978). However, wastewater treatment plants

have better management and maintenance when compared with OSTDSs.

Septic Tank Design and Operation

Quality septic tank design ensures proper operation and treatment of wastewater.

Septic tanks must be designed to promote the separation of solids from the wastewater

effluent. The septic tank must also be at adequate capacity to guarantee retention of

effluent to allow settling and storage of the settled solids. The stored solids are then

subjected to partial treatment by degradation.

Septic tank design

Septic tanks are designed to prevent failure and increase longevity of a drainfield

by preventing solids from exiting. A septic tank has the following components: entrance

and exit baffles, a manhole, and possibly an interior wall (Figure 2-1). The entrance and

exit baffles are designed to allow wastewater to enter the septic tank and clarified effluent

to leave without stored solids exiting. Like a settling chamber, the entrance and exit









baffles are located on the walls of furthest distance to allow adequate retention time and

settling of solids. The manhole allows access to monitor the retained solids, to pump

septage when solids reach capacity, and to inspect septic tank conditions. An interior

wall is used to divide the septic tank into two separate chambers. Multiple chambers

reduce the amount of solids that can exit when the tank is hydraulically overloaded. The

Florida Department of Health regulates the design of septic tanks through the Florida

Administrative Code of Standards. Major criteria for septic tank design by the Florida

Department of Health are as follows:

* must be watertight (64E-6.002(49)),

* can have a single or double compartment (64E-6.013(2)(a)),

* tanks with a double compartment: the first chamber must be 2/3 the total volume
and the second chamber must be 1/3 of the total volume (64E-6.013(2)(a)),

* liquid depth must be at least 42 inches (64E-6.013(2)(b)),

* airspace must be 15% of the effective capacity (64E-6.013(2)(c)),

* the inlet device must enter one to three inches above the liquid level with a
diameter greater than 4 inches and must not extend greater than 33% of the liquid
depth below the water surface (64E-6.013(2)(d)),

* the outlet device must have a diameter greater than 4 inches and extend down
below the water surface between 33% to 44% of the liquid depth (64E-6.013(2)(e)),

* the inlet and outlet devices must be on opposite ends of the septic tank (64E-
6.013(2)(f)), and

* constructed of concrete, fiberglass, corrosion-resistant steel, or other equally
durable material ((64E-6.010(2)(a)(1)).

Concrete septic tanks are the most common constructed septic tanks while

fiberglass septic tanks are used in areas where the heavy concrete septic tanks cannot be

transported. Concrete septic tanks are typically rectangular in shape with a 2:1 length-to-

width ratio (Canter and Knox, 1985). The width of a concrete septic tank generally









tapers approximately two inches from the top to the bottom. The width profile is usually

a taper or a V-bottom profile (Figure 2-2). Although concrete tanks are commonly used,

they have difficulty remaining watertight from corrosion or at the seal of the tank and the

tank lid. A fiberglass septic tank is commonly cylindrical and easily remains watertight

while in service.


Figure 2-1 A Multiple Chamber Septic Tank Schematic


Figure 2-2 Septic Tank Width Profiles (a) V-bottom (b) Taper

Septic tank capacity must be adequate to allow sufficient retention of wastewater

while storing the accumulated solids. The estimated wastewater flow to an OSTDS is 50

gallons per person per day. The effective volume of a septic tank is the volume required

for twenty-four hour retention of entering wastewater and is located between the sludge









and scum layer (Khan et al., 2000). The effective capacity is the volume below the liquid

in the septic tank (64E-6.002(20)). The required minimum effective capacity for a home

is based on the regulated estimated flow of two occupants per bedroom (Table 2-1) and is

outlined by the Florida Administrative Codes of Standards. Minimum effective septic

tank capacities for different average sewage flow are presented in Table 2-2.

Table 2-1 Residential Estimated Sewage Flow*
Single and Multiple family per dwelling Estimated Sewage Flow (Gallons/Day)
1 bedroom with 750 sq. ft. 100
2 bedrooms with 751-1200 sq. ft. 200
3 bedrooms with 1201-2250 sq. ft. 300
4 bedrooms with 2251-3300 sq. ft. 400
*For each additional bedroom or each additional 750 sq. ft., the estimated sewage flow
increases by 100 gallons per dwelling unit.


Table 2-2 Minimum Effective Septic Tank Capacities
Average Sewage Flow (Gallons/day) Minimum Effective Capacity (Gallons)
0 -200 900
201- 300 900
301 -400 1050
401- 500 1200
501- 600 1350
601- 700 1500


Septic tank operation

Primary treatment of wastewater is performed within the septic tank operation,

consisting of separation of settable solids from wastewater, digest organic matter, store

settled solids, and discharge of clarified liquid for further treatment and disposal in the

drainfield. The septic tank separates solids and grease from liquid through gravity

settling or floatation. The wastewater flow is reduced once it enters the tank, allowing

solids to sink to the bottom while fats and grease float to the top (U.S. Department of

Health, Education, Welfare, 1967). The solids that rise to the top of the liquid level









consisting of fat and grease are termed "scum", and the solids that sink to the bottom of

the tank are termed "sludge". The effluent within the septic tank containing scum and

sludge is termed septage. The scum and sludge combined represent the total solids in the

septic tank. Wastewater clarification is promoted by three main design parameters: tank

depth, retention time, and chambers (Canter and Knox, 1985; U.S. EPA, 1980; Barshied

and El-Baroudi, 1974). A large tank depth increases the available depth for storage and

settling (Barshied and El-Baroudi, 1978).

Retention time is the average time that the wastewater spends in the septic tank

from entry to exit and is a function of the effective volume, daily household wastewater

flow, and the volume of stored solids (Kahn et al., 2000). As the sludge depth increases,

the liquid volume and detention time in the septic tank will decrease (U.S. EPA, 1980).

At maximum sludge depth, the septic tank should be able to retain the wastewater for a

minimum of 24 hours (Kahn et al., 2000; U.S. EPA, 1980). However, under ordinary

conditions when the storage is not at capacity, wastewater may be retained in the septic

tank for up to three days (Kahn et al., 2000).

Multiple chambers prevent solids from exiting the septic tank when mixing is

induced by hydraulically overloading the tank. Multiple chambers also decrease mixing

and increase the removal of biochemical oxygen demand (BOD) and suspended solids

(U.S. EPA, 1980). The multiple chambers allow mixing of solids with liquid in the first

chamber, while the second compartment receives wastewater at a lowered velocity

allowing the remaining solids to settle from the wastewater again before effluent exits the

tank (Canter and Knox, 1985). A tank with multiple chambers will lead to longer service

time between pump outs (Canter and Knox, 1985).









Solids storage uses the remaining septic tank volume that is not required for the

effective volume to settle solids. Scum storage is a layer at the top of the liquid level

with two-thirds of the layer above the liquid and one-third of the layer submerged (U.S.

EPA, 1980). Forty percent of the septic tank volume is typically designed for sludge and

scum storage (U.S. EPA, 1980). Maintenance must be performed when the scum or the

sludge layer is endangered of exiting the tank.

Stored solids are partially degraded within the septic tank. The septic tank is an

anaerobic environment, thus the term "septic" (U.S. EPA, 1980; Laak and Crates, 1978;

U.S. Department of Health, Education, Welfare, 1967). The available anaerobic

microbial cultures partially decompose and liquefy solids (U.S. EPA, 1980; Laak and

Crates, 1978; U.S. Department of Health, Education, Welfare, 1967). The

microorganisms in the septic tank destroy pathogens, mineralize organic matter, and

oxidize material (Canter and Knox, 1985), while reducing sludge and scum to finer

particles, liquid, and gas during decomposition and digestion (U.S. Department of Health,

Education, Welfare, 1967; Amerisep Inc., 1999). The major chemicals in the retained

solids are carbon, hydrogen, nitrogen and sulfur that are transformed during digestion and

decomposition to methane, carbon dioxide, water, ammonia, and hydrogen sulfide

(Baumann, 1978, Wilhelm et al., 1994).

Drainfield Design and Operation

The drainfield treats and disposes clarified effluent by distributing it into the soil

for percolation (U.S. Dept. of Agriculture, 1982). The soil type and appropriate sizing

determine treatment performance of clarified effluent in the drainfield. The treatment in

the drainfield is final treatment of the effluent before disposal and is achieved by

percolation and biological degradation.









Drainfield design

The drainfield is designed to discharge clarified effluent into the soil below for

final treatment and disposal (Kahn et al., 2000). The drainfield uses either an adsorption

bed or a drain trench with a mineral aggregate for disposing clarified effluent to the soil

(64E-6.014(5)). The drainfield size depends on of the soil type and estimated

wastewater flow (64E-6.008(5); U.S. Department of Agriculture, 1982). Soil types that

are slightly to moderately limitation are satisfactory for standard subsurface systems that

are determined by a percolation test. A limited soil type is defined as by the percolation

rate with a slightly limited soil having a percolation of less than 2 minutes per inch and a

moderately limited soil having 5 to 10 minutes per inch. Severely limited soil types have

a percolation rate of greater than 30 minutes per inch or less than one minute per inch and

a water table less than 4 feet below the drainfield and are unsatisfactory for standard

subsurface systems because the soil type will not promote the minimum 2 foot

unsaturated soil condition needed for proper treatment (64E-6.008(5)).

A drain trench is the preferred method of subsurface drainfield systems (64E-

6.014(b)). The trench system consists of a perforated pipe discharging clarified effluent

within its own trench (Brown and Peart, 1996). The trench cannot be greater than 36

inches wide (64E-6.014(5)(a)). A trench width less than 12 inches must have a minimum

of 12 inches separating the sidewalls of adjacent trenches (64E-6.014(5)(a)), while a

trench width greater than 12 inches must have a minimum of 24 inches separating the

sidewalls of adjacent trenches (64E-6.014(5)(a)).

An absorption bed system must have the entire earth content of the absorption area

removed and replaced with aggregate and distribution pipes (64E-6.014(5)(b)). The

perforated pipes are all in the same trench, being the single bed. The bottom surface of









the absorption bed must not exceed 1500 square feet (64E-6.014(5)(b)), and the

dimensions of the absorption bed must achieve maximum length-to-width ratio practical

(64E-6.014(5)(b)).

The maximum depth of the drainfield from bottom to finished surface must not

exceed 30 inches with a minimum earth cover of 6 inches (64E-6.014(5)(e)). A polyester

bonded layer is used to prevent earth backfill from infiltrating and is placed only on top

of the drainfield (64E-6.014(5)(e); Brown and Peart, 1996). The mineral aggregate

material that is used within the trench or bed is either limestone, slag, quartz rock,

granite, river gravel, recycled crushed concrete, lightweight aggregate, or another equally

durable material (64E-6.014(5)(c)1). The total depth of aggregate must be at least 12

inches throughout the bed or trench with a minimum of 6 inches below the pipe, but not

exceeding 10 inches when total depth is at the minimum (64E-6.014(5)(c)1). A profile of

a drainfield is shown in Figure 2-3.


Polyester bonded Backfill
layer
12"
-- I "< -- lneral aggregate
Perforated pipe 6" aggregate



Original soil

Figure 2-3 Drainfield Profile


Drainfield operation

Septic tank effluent is discharged into the drainfield for further treatment through

biological processes, adsorption, and infiltration into underlying soil (U.S. EPA, 2002).









The clarified effluent is discharged from perforated pipes through aggregate to evenly

distribute effluent to the soil. Remaining solids (suspended) in the effluent will form a

clogging mat above the soil layer, lowering hydraulic conductivity that prevents soil

saturation (Ayres Associates, 1993; U.S. EPA, 1980). The clarified effluent receives

primary treatment as it percolates through the soil and is disposed of to the water table.

During percolation, clarified effluent is treated by physically entrapping the

remaining particulate matter in the clarified effluent and is responsible for the majority of

wastewater treatment (U.S. EPA, 1980). The clarified effluent percolates through

unsaturated soil to provide adequate removal of pathogenic organisms and other

pollutants from the effluent before reaching the groundwater (Bicki, 1989; U.S. EPA,

1980). The drainfield is responsible for treating organic, inorganics, and pathogens in

the clarified wastewater. Affective treatment is accomplished by a complex arrangement

of primary minerals and organic particles that differ in composition, size, shape, and

arrangement in the soil (U.S. EPA, 1980).

The quality of wastewater treatment depends on how the effluent moves into and

through the soil. Treatment in the soil depends on the soil's physical properties: size,

shape, and continuity of pore space (U.S. EPA, 1980) and is dependent on the wastewater

nature, soil type, and degree of saturation (Brown, 1998). Unsaturated soil forces

clarified effluent to flow through smaller pores, maximizing treatment compared to

saturated soil where smaller pores are occupied by water (U.S. EPA, 1980). The clarified

effluent travels more slowly in unsaturated soil than in the same soil when saturated. The

slower the velocity of flow, the longer the residence time of the wastewater in the









unsaturated soil and the greater the opportunity to treat the wastewater as it travels

through the soil (Brown, 1998).

The two most important soil attributes are soil permeability and seasonal high

ground water table (Brown, 1998). Soil permeability refers to the ability of a soil to

transmit water or air (U.S. Department of Agriculture, 1984). Permeability is based on

the soil characteristics observed in the field, particularly structure, porosity, and texture

(U.S. Department of Agriculture, 1984). Low permeability, such as in clayey soils,

would prohibit vertical flow and would result in horizontal flow with little or no

treatment. A high permeability soil, such as sandy soil, has rapid vertical flow with little

residence time in the unsaturated soil, resulting in limited treatment.

Final disposal occurs when the treated clarified effluent has percolated through

the unsaturated soil and reaches the water table. In areas limited in unsaturated soil

depth, the soil must be built up (mounded) to meet this requirement. Once the effluent

makes it to the water table, its concentration will dilute and eventually make its way to

surface water or a lower aquifer.

OSTDS Maintenance

Inspection ensures that the system is functioning as designed. Pumping the septic

tank should be done when accumulated solids have reached the storage capacity. A

combination of visual, physical, bacteriological, chemical, and remote monitoring can be

used to access system performance (U.S. EPA, 2002). A recurring weakness of many

existing OSTDS management programs has been the failure to ensure proper operation

and maintenance of installed systems (U.S. EPA, 2002).









Annual Inspection

The type of inspection and frequency should be determined by the size of the area,

site conditions, resource sensitivity, the complexity of the system, and number of systems

(U.S. EPA, 2002). Mandatory inspections are an effective method for identifying system

failures or systems in need of corrective action (U.S. EPA, 2002). The inspection would

ensure the system is functioning properly and identify any obvious problems such as the

septic tank structure and accumulated solids level (Crites and Tchobanoglous, 1998; U.S.

Department of Health, Education, Welfare, 1967). Scheduled inspections during seasonal

rises in ground water levels facilitate monitoring of performance during "worst case"

conditions (U.S. EPA, 2002). The OSTDS should be inspected for the following:

1. watertight tank condition,
2. clogs in the entrance and exit baffles, and
3. accumulated sludge and scum levels.

Maintenance Pumping

Tank pumping or other routine maintenance tasks are seldom required or even

tracked by regulatory authorities of management for information purposes (U.S. EPA,

2002). Septic tanks must be pumped when solid layers are above designed storage

capacity to prevent solids from entering the drainfield and ensure proper operation (U.S.

EPA, 1980; U.S. Department of Health, Education, Welfare, 1967). The septic tank

reaches capacity when the retention time is less than twenty-four hours or the sludge

layer is within three inches of the bottom of the exit baffle (U.S. EPA, 1999; U.S. EPA

1980; U.S. Department of Health, Education, Welfare, 1967).

The pumping frequency is dependent on the accumulation rate of solids that vary

from system to system and is a factor of septic tank design, wastewater characteristics,

and drainfield performance (U.S. EPA, 2000b; Vogel and Rupp, 1999; Bounds, 1996;









Mancl, 1984). Recommended pumping frequencies range from 2 to 12 years (Benton

County Environmental Health, 1998; Jones and Yahner, 1992; Loudon, 2002). In some

counties such as Brown County, WI, the pumping frequency is regulated. In this

particular case, tanks are required to be pumped out every three years unless the solids

are less than one-third of liquid capacity (County Codes 11.073(c)(5)(a)). Pumping a

system too often increases the volume of septage that must be unnecessarily treated.

EPA Management Guidelines

The importance of OSTDS management became a national issue when it was found

that improperly operated systems were becoming contributors to major water quality

problems. The U.S. EPA created OSTDS Management Guidelines to raise the level of

performance of OSTDSs through improved management programs (U.S. EPA, 2000).

The management guidelines present five separate model programs as a progressive

series where management requirements become more rigorous as the system technologies

become more complex or when environmental sensitivity increases. The management

guidelines are voluntary and apply to all OSTDSs. The models are structured to allow

communities to pick and choose or adopt complete sets of management criteria that will

provide the necessary level of protection while balancing costs and other institutional

factors. The model programs provided by the U.S. EPA are intended to be benchmarks

that aid communities in identifying a management objective, in evaluating whether

current programs are adequate, and ultimately, in determining an appropriate

management program and the necessary program enhancements to achieve management

objectives and public health and environmental goals.









Previous Solids Accumulation Rate Research

Discussion of Prior Studies

Three previous studies examined solids generation in a septic tank. A study by the

Public Health Service (1949) was the first extensive study, and the results reported in this

study are still consulted today (Bounds, 1992). A second study by Terry Bounds in 1986

was used to validate the results of the Public Health Service. A third study by J. D.

Moores in Novia Scotia was performed in 2002 to examine accumulation rates in

OSTDSs.

United States Public Health Service

The United States Public Health Service (USPHS) presented a study on the

accumulation rate of solids in a septic tank in 1949. The USPHS study used 300 single

family homes with septic systems in 9 areas Dallas, TX; Kansas City, MO; Cook

County, IL; St. Joseph, IN; Cincinnati, OH; Kalamazoo, MI; Warwick County, VA;

Cuyahoga County, OR; Montgomery County, AL; and Dade County, FL. An inspection

was made of each home that had available history on its system. The criteria for

participation was that it

1. must be a single family home,
2. have reasonably accurate history with known last pump out date of the tank,
3. the tank could not be full, and
4. the outlet device must be intact.

The inspection documented the number of people occupying the home, the number of

bedrooms, water usage from the water meter, the discharge units (bathroom, laundry,

kitchen and/or water closet), and the measured solids in the septic tank.

A total of 205 tanks were used in their analysis, with years of service ranging

from 0.5 to 39 years (Table 2-3). The years of service is the time since either the tank









was pumped-out or installed. The mean and median accumulation rates in gallons per

person per year for the participants who had their systems in service for 2 years or less

are provided in Table 2-4. Table 2-4 shows that the accumulation rate in these tanks was

high in the first half year of service, after which it quickly decreased.



Table 2-3 USPHS Septic Tank Years of Service (Weibel et al., 1949)
Years of Service Number of Participants
0.5 4
0.75 4
1 13
1.5 2
2 13
3 24
4 14
5 14
6 30
7 18
8 23
9 19
10 4
11 6
12 5
13 4
16 1
20 3
21 1
32 2
39 1





Table 2-4 USPHS Accumulation Means and Medians (Weibel et al., 1949)
Years of Number Mean Mean Mean Median Median Median
Service of Reports Scum Sludge SC* & SL* Scum Sludge SC* & SL*
0.5 4 17.35 71.44 88.79 19.60 63.06 89.61
0.75 4 2.84 31.34 31.94 0 32.39 34.41
1 13 5.16 18.25 23.41 2.02 16.23 22.59
1.5 2 13.09 8.53 21.62 13.09 8.53 21.62
2 24 4.04 10.17 14.21 2.84 9.35 15.41
SC = scum; SL = sludge.









From the results of the Weibel et al. study, the USPHS concluded that sludge and

scum accumulated more quickly per person in the first 6 years of operation. Sludge

accumulation became constant at the 7-year point, while scum accumulation became

constant at the 3-year point.

Septic tanks with capacities less than 125 175 gallons per person retained fewer

solids than tanks greater than 175 gallons per person. The lower capacity tanks could

result in a lower retention than the larger was because of a lower retention time that

allowed settling of the solids. The increased depth of the liquid level was found to

increase the solid removal from the wastewater that also increases retention time,

increasing solids accumulation. The average accumulation of scum, sludge, and total

solids is presented in Figure 2-3 with values in Table 2-5.




35

30

(De 25

E 0 20 -

S 15 -*
e C Sludge & Sm




0
| | 10 S Sludge
5 3um -- m


0 5 10 15 20 25
Years of Service


Figure 2-3 PHS Rate of Scum & Sludge Accumulation. The points marked on the figure
are from the mean accumulation rate of each year and the trend line marks the
average accumulation over all. (Weibel et al., 1949)









Table 2-5 Total per Capita Sludge and Scum Accumulation (Weibel et al., 1949)


Years


Gallons/ Capita/Year


Total Gallons/Capita


Scum


Scum &
Sludge


Sludge


Scum &
Sludge


1 6.21 18.33 24.54 6.21 18.33 24.54
2 3.52 12.19 15.71 9.72 30.52 40.25
3 3.22 9.58 12.79 12.94 40.10 53.04
4 3.22 8.15 11.37 16.16 48.25 64.41
5 3.22 7.48 10.70 19.37 55.73 75.10
6 3.22 7.11 10.32 22.59 62.84 85.43
7 3.22 6.88 10.10 25.81 69.72 95.53
8 3.22 6.88 10.10 29.02 76.60 105.62
9 3.22 6.88 10.10 32.24 83.48 115.72
10 3.22 6.88 10.10 35.46 90.36 125.82
11 3.22 6.88 10.10 38.67 97.25 135.92
12 3.14 6.88 10.02 41.82 104.13 145.94
13 3.14 6.88 10.02 44.96 111.01 155.97
14 3.14 6.88 10.02 48.10 117.89 165.99
15 3.14 6.88 10.02 51.24 124.78 176.02
16 3.14 6.88 10.02 54.38 131.66 186.04
17 3.14 6.88 10.02 57.53 138.54 196.06
18 3.14 6.88 10.02 60.67 145.42 206.09
19 3.14 6.88 10.02 63.81 152.30 216.11
20 3.14 6.88 10.02 66.95 159.19 226.14


Bounds Study

The Bounds study (1992, 1996) was centered in Glide County, Oregon where the

largest septic tank effluent pump (STEP) system (in the nation) was in place. A STEP

system uses septic tanks (for initial wastewater treatment) in conjunction with a sewer

system (receives clarified effluent from the septic tanks). A pump is in place in the septic

tank that pumps the clarified effluent into the sewer lines. The use of a STEP system

within a septic tank can cause turbulence and washout of solids. The STEP system in

Glide County had 468 septic tanks and over 20 miles of collection lines. A step system,

like OSTDS systems, still needs to be pumped out as solids fill the tank, and the septic

tanks in Glide County were pumped when sludge was within 6 inches and scum was

within 3 inches of the outlet (Bounds, 1992).


Scum


Sludge









In his study, Bounds used 450 tanks in Glide County. Residents were interviewed

and information on the number of people, their ages, and their habits that would impact

performance was gathered (Wilcox, 1992). A total of three measurements were taken in

this study at 2.8 years, 5 years, and 8 years. The first measurement of solids was 2.8

years after initial pump out, and 19 of the tanks were randomly selected for solids

measurement 5 years after pump out. On the third measurement at 8 years after pump

out, solids were measured in all the tanks again. Figure 2-4 illustrates the average

accumulation of total solids in Glide County.

r 120

0 100 -

C. 80 -



0 40-
o 0

20 -.


0 2 4 6 8 10
Time (Years)

Figure 2-4 Bounds Study Volume of Total Solids For Eight Years

As shown in Figure 2-4, after 8 years, the solids levels were at half of the storage

capacity. Bounds (1992) also noted that microorganisms required up to 2 years to reach

solid decomposition activity levels that are high enough to impact accumulation rates.

The results of this study also showed that the infiltration of groundwater resulted in solids

accumulation decreasing and that scum accumulation increased with increased garbage

disposal use. The Bounds Study is the first and only study that observed the









accumulation of solids over an extended period of time, unlike the single inspection made

by the Public Health Service study.

Moore Study

The Moore study (2002) centered in Nova Scotia and presented a literature review

and results of a field analysis of pumping frequencies and maintenance procedures.

Measurements were collected from 40 tanks that had accurate records of the most recent

pump out. The OSTDSs used in this study, ranged in operation time from 0.75 to 12

years from the last pumping and ranged in the occupants it served from 1 to 60

occupants. The mean and median numbers of years of service were 3.64 years and 3

years, respectively, whereas the mean and median occupants in the home were 6.4 people

and 3 people, respectively. The average sludge accumulation rate from those tanks was

10.93 gallons per person per year, and the scum accumulation rate was 5.86 gallons per

person per year.

Table 2-6 Moore Study (2002) Distribution of Years of Service
Years of Service Number of Systems
0.75 1
1 3
1.5 3
2 3
2.5 2
3 11
4 6
4.5 1
5 6
6 2
11 1
12 1









Table 2-7 Moore Study (2002) Scum and Sludge Accumulation Trends
Years Number Mean Mean Mean Median Median Median
of of Scum Sludge SC* & Scum Sludge SC* & SL*
Service Reports SL*
0.75 1 20.36 0 20.36 20.36 0 20.36
1 3 12.09 0.85 12.94 9.16 0 9.16
1.5 3 17.41 7.54 24.94 16.07 9.04 28.12
2 3 17.73 6.53 24.26 22.91 3.05 17.82
*SC = Scum; SL = Sludge.

The results of this study in Novia Scotia were used to educate homeowners in best

management practices. While Moore did not determine significant influences on

accumulation, he but did discuss the effects of system additives and water softener brine.

System tank additives, in some cases, resulted in limitations in solid separation from

wastewater, and systems receiving water softener brine showed a decrease in scum

accumulation.

Comparison of Pump Out Frequencies

The prior studies illustrate the current documented knowledge in the accumulation

rate of solids in the septic tank. A summary of their results is presented in Table 2-8,

which lists the number of participants, the accumulation of scum and sludge in gallons

per capital for the first year, the model equation for total solids, and the solids

measurement method. The accumulations in the first year for the PHS study (1949) and

the Moore study (2002) are similar. Also, the Bounds study (1992) is considered to be in

agreement with the PHS study in terms of accumulation rates, even though the 1-year

sludge and scum accumulation volumes are not available.









Table 2-8 Summaries of Prior Studies
1 year Sludge 1 year Scum Total Solids
Participant Accumulation Accumulation Model* Method of
Study Count Gallons/Capita Gallons/Capita Gallons/Capita Measurement
PHS, 205 18.33 6.21 8.6t + 14.96 Single
1949 Inspection
Bound, Multiple
1992 450 N/A N/A 23.4t07 inspections
during 8 years
Moore, 40 16.94 5.91 22.85t Single
2002 Inspection
* t = time, years.

The volume of total solids accumulated during the first year is within less than 25

gallons per capital for all 3 studies. The PHS and Bounds studies result that the

accumulation rate during the first year is greater than the accumulation rate in subsequent

years. The PHS and Bounds studies also used over 200 participants, with the Bounds

study using twice the number of participants than with the PHS study. Unlike the PHS

and Bounds study, the Moore study had less than 50 participants and had a constant

accumulation rate from the first to the last year (8th).

The shortcomings of these studies were the lack of statistical information and the

method of measurement. Unfortunately, the studies did not present the standard

deviations for the data that was collected. The standard deviation was calculated for the

Moore study with the mean and standard deviation for scum, 23.32 gallons per year and

28.74 gallons per year, respectively, and for sludge, 40.46 gallons per year and 47.78

gallons per year, respectively. The single inspection made during the PHS and Moore

studies assumed that accumulation trends in the OSTDSs are similar. More than one

measurement from a system determines accumulation trends that result in identifying the

accumulation rate peak for each solid. In the Bounds study two measurements were









made, and the peak volume is assumed to be between 2.8 years and 8 years. The Bounds

study was the first to monitor an OSTDS over an extended time period after pump out.

The objective of this study was to determine the accumulation rate for scum and

sludge during the first year of service. The accumulation rate was determined from

multiple measurements of over 200 participants. Performance variables were determined

from wastewater, system design, and surrounding environmental characteristics that

could possibly affect the accumulation and those variables that do affect the system were

to be included in a model to predict solids accumulation. The overall outcome of this

study is an attempt to produce best management practices to control solids accumulation,

along with the expected solids accumulation rate when considering an individual system

in its entirety.














CHAPTER 3
METHODS

Objectives

The objectives of this study were to identify the relevant variables, collecting them

from a select population, develop a model with the collected data and assess the relative

impact of variables to the OSTDS performance. The result of this study is aimed to also

develop best management practices that homeowners can implement. The goals used to

address these objectives was:

* Identify potential performance variables from household activity, system factors,
and surrounding environment characteristics,
* Create a survey to collect identified performance variables from OSTDS-using
homeowners,
* Create a database of the systems to store contact information, collected
performance variables, and inspection measurements,
* Determine expected accumulation rates for scum and sludge,
* Determine what performance factors that impact OSTDS performance, and
* Create a model using performance factors that impact OSTDS performance.


In this study, the OSTDS performance and management practices were monitored

over a sample population of 221 Charlotte County residents to determine the most

significant underlying factors that influence accumulation of solids. Potential

performance-influencing variables were identified and databased by UF using a

combination of surveys, permits, and inspections. After pumping out the participating

homeowners' OSTDS during an initial inspection by CCDOH, the depths of solids were

measured at approximately 6- and 12-month time intervals, and this accumulation

information, transferred to UF, served as the response variable in multiple linear









regression (MLR) models. The Biostatistics Consulting Laboratory in the Department of

Statistics at UF performed all analysis, and the resulting trends showing which variables

influenced solids accumulation were identified.

Task 1: Identification of Relevant Variables

As a first step in better understanding the problem of OSTDS failure and its causes,

all factors influencing accumulation were determined using an exhaustive literature

search of OSTDS care and maintenance fact sheets, reports from previous research, and

manuals for system management. The factors identified in the literature as having

potential impact on OSTDS performance were categorized into three major groupings

describing 1) wastewater characteristics, 2) system design and condition, and 3)

surrounding environment. The wastewater characteristics, consisting of hydraulic

loading and wastewater quality, are factors that describe the wastewater that enters into

the system from the home. The OSTDS system design and condition consists of specific

information on the septic tank and the drainfield. The surrounding environment consists

of the site elevation and groundwater elevation. A more thorough description of each

grouping of factors is provided below.

Wastewater Characteristics

The hydraulic loading and quality of wastewater entering the system from the

home can be best predicted by household practices, such as occupancy, home activity,

home characteristics, and water consumption (U.S. EPA, 2000; Crites and

Tchobanogloos, 1998; Anderson and Siegrist, 1989; Siegrist, 1983). Home activity

varies with occupants' practices and includes water-using appliances and disposal

practices (U.S. EPA, 2002; U.S. EPA, 2000a). Home description factors typically stay

constant despite change in occupancy and include water-conserving plumbing fixtures,









water-using appliances, water source, and home characteristics (U.S. EPA, 2002;

Hammer and Hammer, 2001; Kahn et al., 2000).

Occupancy factors potentially impact water characteristics by the number and age

of residents, annual time of occupancy, and ownership period. The number of residents

significantly alters water consumption and wastewater production (U.S. EPA, 2000). The

annual occupancy duration differentiates seasonal residences that accumulate solids for a

short period from year-round residences, which accumulate solids all year. The seasonal

residences allow the system to rest, resulting in less accumulation; however, a longer

length of residency result in a more acclimated microbial system for decomposing

organic particles, thus decreasing accumulation as well.

Water-using appliances and homeowner practices alter the hydraulic loading and

wastewater quality. Wastewater-creating appliances are typically washing machines,

automatic dishwashers, and garbage disposals, which drain to the septic tank (Kuhner et

al., 1979). Washing machine and dishwasher descriptions alter the hydraulic loading

depending on load capacity and number of loads per week. Water-conserving washing

machines, typically front-loading, use significantly less water compared to traditional

top-loading machines. Detergent type and use, liquid fabric softener, and bleach also

alter wastewater quality.

Kitchen sink activity influences wastewater. For example, removal of solids from

dishes to a solid waste container before cleaning in a sink or dishwasher reduces the

amount of particles exiting through the drain (Kuhner et al., 1979). Garbage disposal use,

therefore, increases solid accumulation by introducing food particles into the system

(U.S. EPA, 2002; Hammer and Hammer, 2001; Bounds, 1996). Also, frying foods









compared to baking introduces a higher amount of oil and fats if the grease from frying is

disposed down the sink drain (U.S. EPA, 2002; Kahn et al., 2000).

Direct disposal of solids other than toilet tissue and non-water liquids increases

solids accumulation. Typical liquids other than water that are disposed in the drain

include paint thinners, pesticides, salad dressing oil, sour milk, disinfectants, bleach, and

food grease. Typical solids that are improperly introduced in the wastewater system are

feminine products, disposable diapers, plastic items, nylon products, medications, rubber

products, cigarette filters, paper towels, and any type of food item (U.S. EPA, 2002;

Hammer and Hammer, 2001; Lesikar, 1999a).

System Design

System design components are functions of the septic tank and drainfield (Lesikar,

1999b; Laak, 1980). The septic tank's age, dimensions, tank volume, number of

chambers, and number of tanks along with the drainfield configuration, area, and

elevation are included in this study. System age is used to note an impact of

performance, especially with the many systems in the nation over 30 years old. The

drainfield description is used to determine if the drainfield impairs or promotes the

performance of solid accumulation. When a drainfield is not operating correctly and

drainage is not occurring, water can reenter into the septic tank allowing solids to exit.

Bounds (1996) noticed this effect from high groundwater levels on accumulation in the

septic tank. The elevation of the drainfield is in relation to the elevation of the center of

the paved frontage road of the residence.

Surrounding Environment

The surrounding environment factors that potentially hinder system performance

are site elevation and the contact surface of the tank or drainfields with the groundwater.









The elevation of a system determines its ability to drain and the possibility of water

infiltration. Systems in contact with groundwater can cause infiltration in leaky tanks

(Bounds, 1996), while storm and floodwaters that flood drainfields can cause infiltration

to both leaky and non-leaky tanks. The estimated water table is the water level that is

expected to be in a year of normal rainfall during the wet season characterized by zero

pore pressure or simply described as the water level in an unlined, augered hole at the end

of the wet season in a year of normal rainfall.

As previously mentioned, the purpose of the literature review phase of this project

was to construct a thorough list of all potential factors that may impact OSTDS

performance. The potential performance variables that were included on this list are

presented in the results chapter to follow. Values of each these variables were

subsequently obtained by a combination of surveys of selected participants, permits, and

inspections.

Task 2: Selection and Recruitment of Participants

Three criteria were used in choosing participants. First, a participant should live in

a region with dominant soil type containing 2% or more of the total population of

OSTDSs in Charlotte County. Using systems within these "most populated" soils would

ensure representation of a majority of Charlotte County's OSTDS population. However,

because of the unanticipated difficulty that CCDOH would have in visiting the large

number of widely distributed OSTDSs, a second criterion was followed that participants

would live in only one largely populated region of Charlotte County in proximity to

CCDOH. Finally, the third criterion was the willingness of the selected residents to

participate in this study. Below is a detailed description of how participants were

randomly selected and recruited to participate in this study.









Subtask 2A: Participant Selection

Location of systems in Charlotte County

The Charlotte County GIS (CCGIS) Department located homes with OSTDSs from

sewer line data and property parcel information obtained from the Charlotte County

Property Appraisers. The property parcel information and the sewer line data were then

transferred to a map of the region to identify which homes have sewer services or

OSTDSs. Properties that were in contact or adjacent to the sewer lines were considered

sewer-using properties. The remaining properties were then identified as OSTDS-using

properties.

Identification of OSTDS density by soil type

A map showing which residences possessed OSTDSs was subsequently overlayed

with soil types in Charlotte County using ARC GIS software (ESRI, Redlands, CA,

USA). The resulting map, Figure 3-1, allowed counting of the number of OSTDSs in

each soil type and, ultimately, the determination of which soil types contained the most

systems.

Random selection of potential participants

In response to a request by CCDOH, one specific area of Charlotte County was

chosen for the study to ease accessibility for pump-outs and solid measurements. This

region, Mid-County 2 (MC2), was selected for its proximity to CCDOH and high density

of OSTDSs (refer to Figure 3-1). Forty-five percent of the county's systems (and nearly

50% (20,822) of the systems when considering "most populated" soils only) are in MC2.

The CCGIS Department randomly extracted 2,300 systems from their database using

ARC GIS utilities. The property identification number was cross-referenced with the

property appraiser's database to extract the owner's name and mailing and physical









addresses, and this information was transferred to a master Access (Microsoft, Mountain

View, CA, USA) database.

Subtask 2B: Recruiting of Participants

Recruitment efforts began in October 2001 and ended in June 2002 using a

combination of methods as described below.

Newspaper article

In March of 1999, the Charlotte Sun Herald published an article announcing the

pilot program that will involve 400 OSTDS users. The article provided contact

information for interested homeowners. Also, residents were informed of a free septic

tank pump out for their participation.

Mailing campaign

The mailing campaign was focused on residents with OSTDSs selected by the

CCGIS Department. The volunteers who responded to the newspaper article were also

included in the mailing campaign. The mailings consisted of a postcard followed by a

delivered package one week later. The postcard informed the residents of the study and

that they would soon be receiving a package within the following week. The packages

consisted of the following items:

1. a flier describing what was requested of the participants and how the gathered
information would be used (Appendix A),
2. two consent forms: one for the resident's record and one to sign and mail back
(Appendix A),
3. the initial survey (to be discussed below),
4. a self-addressed and stamped return envelope, and
5. a pamphlet on system care.













Charlotte County
Dwellings wllhout Sewer by Soil Type
VA .rf .



C. 4.,4
:$ -&,


Figure 3-1 Selected Systems in Mid-County 2 Basin per Soil Type


I 1


L


r


Z,. o ..... i i'.m ......









A followup postcard was mailed a month after the survey to remind those

participants not responding to the mailings to do so as soon as possible. Five mailings

totaling 1,512 packages were mailed from October 2001 to May 2002 in order to recruit

participants.

County fair

A booth at the Charlotte County Fair was used for recruiting from February 15-23,

2002. CCDOH and UF staff manned the fair booth and provided educational information

on system operation and maintenance and was used to invite residents to participate in the

study. Residents who volunteered to participate completed the consent form and initial

survey at the booth and received a pamphlet, flier, and a copy of the consent form.

Although the mass mailings and newspapers were distributed to many, the results

were relatively poor for participant recruiting. The fair booth was the best method for

recruiting participants, most likely because most people feel more comfortable receiving

information in a personal conversation where they can have their questions answered

with an immediate response rather than from passive sources, such as the fliers mailed

and articles printed in the newspaper that placed the burden on them to call for additional

information.

Subtask 2C: Division of Recruits into Phase 1 and Phase 2 of the Study

The list of participants in the study was divided into two phases, and, in doing so,

care was taken to make certain that Phase 1 and Phase 2 contain an even distribution of

the studied performance (independent) variables. The groupings of the participants were

randomly prepared taking into account only information received in the initial survey of

household characteristics. To ensure even distribution of characteristics, both qualitative

data denoted by "yes" or "no" (e.g., washing machine draining to septic tank) and









quantitative data (e.g., number of people per home) were divided. The quantitative data

were first converted to two levels, high (H) and low (L), depending where they fell in

relation to a median value. The resulting percent distribution of high and low levels of

each was maintained for both Phases 1 and 2. These results will be discussed in Chapter

4.

The pump out date was also used to separate the phases so that participants whose

systems were the first to be pumped would be in Phase 1, while those whose systems

pumped last would be in Phase 2. The pump out date ensured that Phase 1 final

measurements would be completed in a timely manner for subsequent analysis. There

were 179 Phase 1 participants and 42 Phase 2 participants.

Subtask 2D: Data Collection and Databasing

As previously described, the independent variables for the constructed model are

the performance variables that have potential to significantly impact system performance,

represented in this study as accumulation rates. The performance variables were

collected by means of surveys, permits, and inspections. Survey information was mostly

completed by mail, but could have been completed in person or by telephone.

Initial survey

With consultation with Dr. Chris McCarty of the UF Survey Research Center in the

Bureau of Economic and Business Research and reference to previous CCDOH surveys,

special consideration was taken in the design of the initial survey in order to enable each

OSTDS owner to accurately provide as many of the potential performance variables for

each system as possible. As previously described, the initial surveys were sent to

prospective participants in Charlotte County from December 2001 to June 2002 after

receiving approval from the UF Institutional Review Board (IRB). The initial survey,









shown in Appendix B, allowed collection of information on residency, home activity,

home description, and surrounding environment.

Follow-up survey

A followup survey, also approved by UF's IRB, was sent to the participants to

clarify answers to questions that were asked in the initial survey, to ask more detailed

questions, and to note any changes in habit. Most participants mailed their surveys back,

while others were called to complete the survey by phone. The followup survey was sent

to participants within 6 months to one year after they had received the initial survey, and

a copy of the followup survey is provided in Appendix B.

Permit information

Permits of most of the participants' OSTDSs were obtained from CCDOH, and

information concerning system description and characteristics of the surrounding

environment was gleaned from these documents and transferred to the Access database.

It is important to note that, of the 221 participants, 25 permits could not be located. As a

result, the system and environmental data were either left blank or estimated.

Inspection information

Initial inspections of each participant's OSTDS were performed by CCDOH as a

means of judging eligibility for participation in the project. Their criteria for eligibility

was that the system could not be experiencing a failure, must operate properly, and have

an intact outlet-tee. While at each home, CCDOH was also able to collect valuable

information for the modeling phase, including the corrosion condition and water

consumption. Also during the initial inspection, the septic tank was pumped out, the tank

condition evaluated, and water use determined.









Height measurements

After the initial inspection, two measurement inspections were performed at 6 and

12 months to obtain the change in height of scum, sludge, and liquid in the tank. The

CCDOH personnel used a raven meter to measure sludge height and a measuring tape to

measure the height of scum. A raven meter is a device that uses light to detect solids.

When light is blocked by solid particles in the tank, it is assumed that the sludge blanket

begins at that elevation. The scum is not uniformly thick in the tank, and the average

thickness must be estimated. Measurements were taken at the exit end of the tank, unless

the septic tank was a multiple chamber tank where measurements were taken in the first

chamber.

Databasing of all variables collected

An Access database was created to contain the data collected for each participant.

The database was first created to include the 2,300 OSTDS homes randomly selected by

the CCGIS Department. Mailing labels were created from the database for recruitment

from those 2,300 OSTDS homes. Separate forms in Access were created for entering

data from the initial and the followup surveys for ease and efficiency.

Task 3: Calculation of Solids Accumulation

A primary focus of this project was assessment of the relative significance of the

collected performance variables (independent variables) on the measured solids

accumulation (dependent variables). Before regression analysis could be performed, the

data needed to be converted to the proper format. The description below provides details

of how the solid height data were used to calculate 6- and 12-month accumulation rates.

In order to begin creating a model, it was necessary to translate a change in sludge

and scum heights to a volume change. With these volume changes in hand, an









accumulation rate of sludge and scum was determined. A discussion of how these

volume rates were calculated follows.

Subtask 3A: Determination of Tank Dimensions

The tank volume and manufacturer for each participant was collected from permit

information. Tank schematics were collected from the CCDOH and Mr. Paul Booher of

the Florida Department of Health located in Gainesville, Florida. A total of 10 different

manufacturers' tanks were present in the study; however, only 8 of the manufacturers'

tank schematics, giving dimensions, were located. Twenty-seven participants either had

no tank information or had unavailable schematics, making it necessary to estimate tank

dimensions. Two methods were used to estimate dimensions depending on the tank

volume. Figures 3-2 and 3-3 illustrate the dimensions of V-bottom and taper-side tanks

(respectively) with the appropriate nomenclature. The taper-side tank maintains a

constant sidewall slope from the inlet to the bottom of the tank, unlike the V-bottom tank

that has 2 different sidewall slopes with the slope being greater at h3 than at h2.

Those tanks with no available dimensions and less than 600 total gallons volume

(representing 2.3% of the 221 OSTDSs in this study) were assumed to have a 2:1 length-

to-width ratio, a 2-inch taper to the bottom, and a 15% airspace volume. The tank's

average surface area was calculated from the tank's volume divided by the liquid height.

The method used to calculate the tank dimensions shown in Figure 3-2 and 3-3 is

provided in Appendix D.

Those tanks with no available dimensions (22 systems total) and volumes of 750,

900, and 1050 gallons were assumed to have the same average dimension ratios as the

same size tanks of known dimensions. The height from the entrance baffle to the lid and

the outer wall width were estimated and assumed constant for each corresponding tank










volume. The estimated dimensions were calculated using lid width and length, liquid

height, along with the dimension relationships for each tank volume. The following

dimension relationships noted in Figures 3-2 and 3-3 were calculated:


p p------------k


a. -
w3


Figure 3-2 V-bottom Septic Tank Schematic with Dimensions (a) width profile (b) length
profile (wi is the width at the top of the tank; w2 is the width at the top of the
sharp bottom taper; w3 is the width at the bottom of the tank; 11 is the length at
the top of the tank; 12 is the length at the top of the sharp bottom taper; 13 is the
length at the bottom of the tank; hi is the height from the top of the tank to the
liquid level, h2 is the height from the liquid level to the top of the sharp
bottom taper; h3 is the height from the top of the sharp bottom taper to the
bottom of the tank)


W .


hb



h2 + h3 HL



b. -


a. W3
w3


Figure 3-3 Taper-Side Septic Tank Schematic with Dimensions (a) width profile (b)
length profile (wi is the width at the top of the tank; w3 is the width at the
bottom of the tank; 11 is the length at the top of the tank; 13 is the length at the
bottom of the tank; hi is the height from the top of the tank to the liquid level,
h2+h3 is the height from liquid level to the bottom of the tank)


hl


h2 HL
12

I<- F -- --- ,,










1. R1 = w2/w3
2. R2 = h2/h3
3. R3 = (w2-wl)/(hl+h2)
4. R4 = (13-11)/(hi+h2+h3)
5. hi
6. t (thickness of wall)

The dimension parameters, wi, W2, and w3, represent the inner width dimensions,

wi at the top of the tank, w2 in the middle, and w3 at the bottom of the tank. As noted in

Figure 3-4, the w2 inner width dimension was chosen at the change in slope for V-bottom

profiles, and at a set distance from the bottom in taper profiles. This established distance

used in taper profile tanks was 10 inches. The inner depth was also presented at these

distances, defined as li, 12, and 13, and 12 being the length in the tank at the break in slope

like w2. The height dimension parameter is based on the inlet baffle. The distance from

the top of the tank to the center of the inlet baffle is termed hi. The distance from the

center of the inlet baffle to the break where 12 and w2 is measured is termed h2. The

distance from the bottom of the tank to the break where h2 ends is termed h3.

Subtask 3B: Calculation of Solids Volumes in Each Tank

Solids accumulation was calculated using height measurements obtained during

measurement inspections. Scum and sludge heights in each participant's tank were

measured by CCDOH in inches and converted by UF to a volume in gallons based on

tank dimensions.








W4


V/


4


W3 13
Figure 3-4 Height Dimensions for Liquid Height (HL), Scum Height (hs,), and Sludge
Height (hsl)
The analytical solutions to calculate solids volumes in a V-bottom septic tank and a
taper-side septic tank are given in Equations 3-1 and 3-2. The dimensions used in the
analytical solutions are illustrated in Figure 3-4, which also demonstrates liquid height
(HL), sludge height (hsl), and scum thickness (hsc). All dimensions and solid and liquid
heights represented in units of inches, and the resulting volume is in units of gallons.


(EQN 3-1)
if hsi < h3 use

VSL = 2w3 *h, 213 2 *h, /231
14 h3 h3

and if hsi > h3

=h3 (W3W2)(13 +12)+

[(h, 2w2 + (W (h h3 ) 212 + 2 )(h, h3. ]
L 4 (hi + h+2 ]) (h2 + hi)


(EQN 3-2) V, = Ihs,1 w -L(-W3) /231
1 hi +h2 +h3 hi +h2 +h3









The sludge calculation in the tapered-side tanks was based on the trapezoidal width

profile. Sludge heights less than h3 were calculated with the top of the sludge blanket as

the top of the trapezoid and the bottom of the tank, and the trapezoid area is multiplied by

the average length of the tank between the top and bottom of the trapezoid. For sludge

depths greater than the h3, the volume is calculated by adding the volume of the lower

trapezoid (top and bottom of h3), and the volume of the trapezoid between the top of h3 to

the top of the sludge blanket. The scum volume was calculated by the scum thickness

multiplied by the width and length of the tank at the liquid height (HL).

Subtask 3C: Calculation of Accumulation Rates

Two different methods were used to determine solids accumulation rates. An

accumulation rate was calculated for the first six months and second six months (using

the change in volume over time) while another accumulation rate was determined using

all three data points (0-, 6-, and 12-month solids volumes) using the least squares method.

Accumulation rates were calculated on a per system basis and a per person basis.

Subtask 3D: Assessment of Trends in Accumulation

The accumulation of solids during the first year of service was evaluated for trends,

by plotting the volume of solids from the time the septic tank was pumped. The

accumulation trends were assessed for a decrease, no change, or increased change in

volume from 6 months to 12 months and grouped accordingly. The accumulations that

increased were grouped by comparing if the change in volume during the first 6 months

was equal to, greater than, or less than the change in volume during the second six

months. The first-year accumulation rate was evaluated for the number of people in the

home, the septic tank size, and the capacity of the septic tank.









Task 4: Interpretation of Phase I and Phase II Model Results

The accumulation rates and performance variables were subsequently subjected to

correlation analysis in order to quantify the influence of each performance variable on

OSTDS performance. The correlation analysis and model development were performed

by Dr. Gary Stevens of the Biostatistics Consulting Laboratory (BCL) in the Department

of Statistics at the University of Florida. The specific methods used are described below.

Subtask 4A: Assess Sample Size

The mean and standard deviation values of the linear accumulation rates were

evaluated to determine if the sample size used was statistically significant. There are two

considerations in determining the appropriate sample size: the tolerable error that

establishes the width of the interval and the level of confidence. The tolerable error was

based on the smallest increment of measure.

In most cases, a confidence interval of the mean was too wide. The solid

accumulation is based on a vertical measurement and tank dimensions. However, the

measurement is only accurate to 1/4-inch. A 1/4-inch error can cause error in the solid

volume accumulation rate that can range from 0.002 to 0.009 gallons per day, depending

on the tank dimensions. An average of possible accumulation rate error for each tank

was used for the margin of error when calculating the significant sample size needed for a

95% confidence of the population mean. The sample size is calculated from Equation 3-

3 (Ott and Longnecker, 2001). The sample size equation is based on an estimated

standard deviation (c), confidence interval (u.), the tolerable error (W), and the Z statistic

(Z./2).









(Za / 2 )2 2
(EQN 3-3) (W/2)2


Subtask 4B: Assessment of Correlations

Correlations determine if a relationship exists between two variables. A

correlation was done for the potential performance variables to predict accumulation and

trends. A correlation measures the strength of the linear relationship between the two

properties and the stronger a correlation is; the better the variable is in predicting the

accumulation. The relationship is determined by the coefficient of determination, r-

square. A value of zero indicates that no predictive value in using the variable and a

value of 1 indicates perfect predictability (Ott and Longnecker, 2001).

Correlation analysis to determine the relationships between the accumulation rates

and performance variables was conducted using accumulation rates of all the systems

together and using rates divided into two specific groups. Dr. Stevens used the Statistical

Analysis Software (SAS) to perform linear correlations of the performance variables to

the accumulation rate.

The two groups rates, termed as "excessive" and "not excessive," were chosen

based on the differences in accumulation observed. Distribution plots provided a visual

means of dividing the rates into these two categories.

Subtask 4C: Assessment of Model Results

The accumulation model was calculated by multiple linear regressions that relate

the accumulation rate to a set of performance variables. The multiple regression model

that best predicts the accumulation rate is indicated by the coefficient of determination.

A coefficient of determination, r-square value, of 0.400 was the assumed cutoff value that






51


shows a relation when correlating variables, but a 0.700 was the cutoff value for a

significant model. The r-square value used as the cutoff limit is based on the 0.6 being

the minimum value that a scatter plot shows a relationship between the variables and

accumulation rates. Using a 0.4 value for correlations ensures that all correlating

variables will be included. A 0.700 value used as an r-square cutoff value makes the

model have a mandatory relationship without being too stringent














CHAPTER 4
RESULTS AND DISCUSSION

Task 1: Identification of Relevant Variables

As discussed in Chapter 3, the purposes of the literature review stage of this project

were to not only to assess current knowledge of OSTDSs and their best management but

also to identify any potential variables that may impact their performance. A large group

of these "performance" variables were assembled and grouped into three basic categories,

wastewater quality/hydraulics, systems design and condition, or the surrounding

environment, as previously described. Figure 4-1 provides a breakdown of these

variables into their respective groupings. For example, occupancy characteristics, the

source and amount of water used, the type of water-using appliance, and the type of

disposal practices may impact wastewater quality and hydraulics. It should be noted that,

of all of products disposed of (solids and liquids) listed under Disposal Practices, none

were considered in the modeling portion of this project; however, information on these

specific disposal activities (e.g., disposing of medications in the toilet) was collected

from each participant via the surveys. These activities provided a general overview of

the awareness that the participants had on the impact of their activities on OSTDS

performance.








53









Occupancy -System Age -Site Elevation
-Septic Tank -Water Table
Number of residents
Occupancy per year Volume Normal water table
Length of time in home Chambers Seasonal High water table
Age of residents Number of tanks Flooding
Water Use -Average length Near surface water
Average width
Water source Drainfield
Water quantity used
-Water-Using Appliances Area
Configuration
-Dishwasher IElevation
Repairs
-Care and Maintenance
capacity
detergent
loads Knows system's location
-Washing Machine Drives or parks on system
Plants on system
capacity System additive
water-conserving
detergent
fabric softener
bleach
loads
Garbage Disposal
Plumbing Fixtures

SShower
Toilet
Disposal Practices


Solids Liquids


feminine products paint thinner
disposable diapers pesticides
plastic products cooking oil
nylon sour milk
medication disinfectants
rubber products bleach
coffee grinds sour milk
cigarette filters
food particles
paper towels
Figure 4-1 Divisions of Performance Variables into the Three Characteristic Groups


These variables were broken down further into those that were quantitative in


nature (requiring an actual numerical value) or qualitative in nature (e.g., yes/no, on/off),


as shown in Tables 4-1 to 4-3 for all three larger categories of variables. Those variables


that were qualitative in nature were designated by a "0" to represent "no," or "off," or a


"1" to represent "yes," or "on." For example, if the participants did not drive on their









drainage location, this would be signified by a "0," and, if their systems experienced

flooding over the OSTDS after rainfall events, this variable was denoted by a "1,"

meaning "yes." In some instances, additional numbers were used for qualitative

variables. For example, dishwasher capacity is a qualitative variable used, where 0

signified that the homeowner does not have a dishwasher, 1 signified a compact capacity,

and 2 signified a standard capacity.


Table 4-1 Potential Performance Factors Describing Wastewater Quality and Hydraulics
Description* Data Type Quantitative Units
Residents (RI) Quantitative Capita
Residents under 11 years (R2) Quantitative Percent
Residents 11 to 19 years (R3) Quantitative Percent
Residents 20 to 69 years (R4) Quantitative Percent
Residents over 70 years (R5) Quantitative Percent
Occupancy (HM1) Quantitative Months/year
Length in home (HM2) Quantitative Years
Water Source (HDI) Qualitative 1/2/3
Water Consumption (HM21) Quantitative Gallons per day
Dishwasher-Capacity (HD11) Qualitative 0/1/2
Dishwasher-Detergent (HM8) Qualitative 0/1/2/3/4
Dishwasher-Loads (HM7) Quantitative Loads/week
Washing Machine-Capacity (HD9) Qualitative 0/1/2/3/4
Washing-Machine-Detergent Qualitative 0/1/2/3
(HM5)
Washing Machine-Water Qualitative 0/1
Conserving (HD10)
Washing Machine-Fabric Softener Qualitative 0/1
(HM6)
Washing Machine-Bleach (HM4) Quantitative Cups/week
Washing Machine-Loads (HM3) Quantitative Loads/week
Garbage Disposal Use (HM9) Qualitative 0/1/2/3
Plumbing Fixtures-Toilet (HD5) Qualitative 0/1
Plumbing Fixtures-Showers (HD6) Qualitative 0/1
Disposal Practice-Solids (HM12) Qualitative 0/1


Disposal Practice-Liquid (HM13)
* Items in parenthesis are abbreviations used to denote these factors


Qualitative











Table 4-2 Potential Performance Factors Describing System Design and Condition
Description* Data Type Quantitative Units
System Age (SD1) Quantitative Years
Septic Tank -Volume (SD2) Quantitative Gallons
Septic Tank Chambers (SD3) Quantitative Chambers/tank
Septic Tank -Quantity (SD4) Quantitative Tanks/home
Septic Tank-Average Length (SD9) Quantitative Inches
Septic Tank-Average Width (SD8) Quantitative Inches
Drainfield-Surface Area (SD5) Quantitative Square Feet
Drainfield-Configuration (SD6) Qualitative 12
Drainfield-Elevation (SD7) Quantitative Feet
Known Repairs to System (HD7) Qualitative 0/1
Care-System Location (HM10) Qualitative 0/1
Care-Drives or Parks on System Qualitative 0/1
(HM11)
Care-Plants on System (HD8) Qualitative 0/1
Care- System Maintenance (HM20) Qualitative 0/1
*Items in parenthesis are abbreviations used to denote these factors.

Table 4-3 Potential Performance Factors Describing Surrounding Environment
Description Data Type Qualitative Units
Site Elevation Quantitative Feet
Water table-Normal Quantitative Feet
Water table-Seasonal Quantitative Feet
Flooding of OSTDS After Rain Qualitative 0/1
Event
Within 75 ft to surface water Qualitative 0/1


Task 2: Selection and Recruitment of Participants from a Select Population of
Charlotte County OSTDS Owners

Subtask 2A: Selection of Potential Participants

As previously described, the CCGIS Department used ARC GIS methods to locate

OSTDSs throughout the county. Figure 4-2 shows a map of Charlotte County's Mid-

County Basin 2 (MC-2) of the selected homes having OSTDSs. A total of 43,311 homes

using OSTDSs in 2001 were located, and this database was layered with the county soil

information to determine the amount of OSTDSs for each soil type present in Charlotte









County. Soil types with 2% or more of the County's OSTDS population were considered

to be the "most populated" soil types (defined as those types with the greatest number of

OSTDSs), and Table 4-4 shows those soil types with the greatest number of OSTDSs.

For a single soil type, the greatest number of systems (18.7%) was located in Oldsmar

Sand with 8094 systems. In alignment with the criterion that the project focus on systems

in these "most populated" soils, potential participants were subsequently randomly

selected from these areas in MC2.


Table 4-4 "Most Populated" Soils (with Largest Number of OSTDSs) in Charlotte
County
Soil Soil Name County Percent of
ID Population Population
36 Immokalee-Urban Land Complex 1866 4.2 %
43 Smyrna Fine Sand 4009 9.3 %
11 Mayakka Fine Sand 2451 5.7 %
28 Immokalee Fine Sand 3887 9.0 %
69 Matlacha gravelly fine Sand 2531 5.8 %
26 Pineda Fine Sand 2747 6.3 %
7 Matlacha-Urban Land Complex 6005 13.9%
33 Oldsmar Sand 8094 18.7 %
12 Fedla Fine Sand 1114 2.6 %
13 Boca Fine Sand 4425 10.2 %
34 Malabar Fine Sand 1341 3.1 %
42 Wabasso Sand, limestone substratum 2931 6.8 %

Subtask 2B: Recruit Participants

Because many of the addresses of the randomly selected homes obtained from the

ARC GIS database were not updated or did not contain OSTDSs or even homes, it was

necessary to repeatedly select new participants and mail initial information concerning

this program (see Appendix A). Another method of approaching potential participants

was by recruiting methods, as previously discussed. Recruitment ended in June of 2002

with a total of 292 willing residents. Table 4-5 illustrates the number of participants from



















Charlotte County
Dwellings without Sewer by Soil Type


*~ h** *S
6 a
S. *



Sn -


~

-.'. ~.
4

t


4-
A


i ~




~ ~

A.
~ S.
~ ,~ ~$


4k


i~
* '*
*.,% ~


L ~7- a


Figure 4-2 Selected Homes having OSTDSs within Mid-County-2


0


I









S~ t~A~






*4


:.


. L -nL-











each recruitment event. All volunteers who approached CCDOH after hearing or reading

advertisements or who were recruited during initial inspections of neighboring homes

(except the ones recruited from the county fair) were combined with the randomly

selected group for the mailing campaign. At one participant's home during the

inspection, five interested neighbors joined the study and had their systems inspected and

pumped the same day. The best recruiting method was by face-to-face contact (at the fair

and during inspections), and the fair booth also enabled contact with residents that

received information from the mailing campaign.

Table 4-5 Recruitment Results
Recruitment Event No. Recruited Participants
Mailing Set #1 32
Mailing Set #2 15
Mailing Set #3 61
County Fair 98
Mailing Set #4 51
Mailing Set #5 35
Total 292


At the end of the first inspection, 238 participants remained in the study. The 54

participants that were no longer in the study either withdrew or were not eligible because

of the condition of their system or the conversion to sewer in the next year. At the end of

the 12 months, 221 participants remained with 179 in Phase 1 and 42 in Phase 2. The 29

participants dropped from the program between June 2002 and June 2003 because tank

information could not be obtained (preventing volumes to be calculated), system failures,

or the property owner had their system pumped during the study.

During the initial inspections by the CCDOH, 25 percent of the systems needed

repairs. Ten percent of the systems had broken off or missing outlet tees. Seventeen









percent of the systems had bad seals between either the manhole and the lid or the lid and

the top of the tank. Ten percent of the systems had holes in the tank, a result of the

sulfate content of the wastewater entering into the septic tank, where anaerobic

conditions, high-strength wastewater, low-flow velocity, and long retention time

promotes the production of H2S, thus leading to the corrosion of tank walls (Fan et al.,

2001).

Subtask 2C: Separation of Recruits into Phase 1 and 2

As mentioned previously, 221 residents were recruited or volunteered to participate

in this study, as a result of the vigorous recruiting and advertising campaigns. Of this

total count, 42 were selected to participate in Phase 2, designed specifically to validate

the results of Phase 1. As a result, their systems were initially inspected and pumped out

subsequent to the Phase 1 systems.

The distribution of the collected quantitative and qualitative data obtained for all

238 initial recruits and their systems is presented in Tables 4-6 and 4-7. As previously

described, care was taken in separating Phase 1 and 2 groups to maintain these

percentage breakdowns of the number of systems in the low and high ranges of each

factor. For example, as shown in Table 4-6, the percentage of all homes with 1-2

occupants was 63% ((149/238)* 100), and this was the target percentage used in both

Phases 1 and 2, as shown in Table 4-8 with 125 out of 198 for Phase 1 and 24 out of 40

for Phase 2.

The median number of occupants per house was 2, and each home prepared a

median number of washing machine and dishwasher loads of 4 and 2, respectively (Table

4-6). Of interesting note in Table 4-7 is the large number of systems with plants on or

near the drainfield, flooding, drainage from the washing machine, and the large numbers









of occupants who dispose of liquids and solids down their sink drains. On the other hand,

46% of the participants had water-conserving toilets and showerheads, and 95% reported

to have knowledge of the location of their OSTDSs. Refer to Appendix C for further

detail on the separation of the recruits into the 2 phases.

Table 4-6 Distribution for Quantitative of Household Characteristic for All Recruits
Factor Factor Count Median Low Low High High
ID Value Count Value Count
Range Range
R1 People per home 238 2 1-2 149 3-12 89
HM1 Time of Occupancy 238 12 0-11 19 12 219
(months)
HM3 Washing machine loads 238 4 0-4 121 5-28 117
HM7 Dishwasher loads 238 2 0-2 123 3-10 114


Table 4-7 Distribution for Qualitative of Household Characteristics for All Recruits
Factor Factor Count
ID
Qualitative Factors City Well Both
HDI Water Source 238 195 35 8
Qualitative Yes/No No Yes
HD2 Washing machine drains to septic tank 238 33 205
HD5 Water-conserving toilets 235 126 109
HD6 Water-conserving showers 235 126 109
HD7 System repair or replacement 234 97 137
HM10 Location knowledge 237 10 226
HM11 Parking or driving on system 237 235 2
HD8 Plants on drainfield 235 153 81
E5 Systems within 75' of surface water 236 219 17
HM12 Disposal of liquids 238 121 117
HM13 Disposal of solids 238 63 174
E4 Flooding 238 22 216


Subtask 2D: Data Collection and Databasing

As previously described, the independent variables to be used in the modeling

phase were obtained from an initial and follow-up survey, permits, and inspections. The

initial survey was successfully completed and returned from the participants, and the









Table 4-8 Frequencies for Each level of Household Characteristics for Each Phase
Factor ID Phase 1 Phase 2
Low High Low High
R1 125 73 24 16
HM1 17 181 2 38
E4 179 19 37 3
HM3 103 95 18 22
HM7 100 98 23 17
City Well Both City Well Both
HDI 164 29 7 31 8 1
No Yes No Yes
HD2 30 168 3 37
HD5 105 90 21 19
HD6 83 111 14 26
HD7 181 10 38 2
HM10 7 190 3 37
HMI11 196 1 39 1
HD8 127 68 26 14
E5 184 12 35 5
HM12 51 147 12 28
HM13 100 98 21 19



follow-up survey was completed and returned by all but 27 participants. Many of the

participants had to be contacted in person or by telephone to have the follow-up survey

completed. Permits were not available for 6 participants; therefore, their systems had

missing factor data for the system design and surrounding environment factors. The

height measurements used for the dependent variable in the subsequent statistical analysis

were gathered during inspections approximately 6 and 12 months after pump out, as

previously described. One home's OSTDS was not measured at 6 months because the

water consumption was less than 200 gallons. All data, both the solids management and

performance factors, were transferred and stored in an Access database.









Task 3: Calculation of Solids Accumulation

Subtask 3A: Calculation of Tank Dimensions

Of the total of 221 tanks studied, 27 did not have readily available dimension

information, thus necessitating calculation of these parameters. As previously described,

two methods were used to calculate dimensions. Method 1 simply required the tank

volume and liquid height and was used for calculating dimensions of 5 tanks with

volumes less than 600 gallons. Method 2 was more complex (and, perhaps more

accurate) using dimension ratios and was used on the remaining 22 tanks with volumes

greater than 750 gallons. The manufacturer's tank dimensions and the estimated

dimensions using the two methods described above are presented in Appendix D of this

document.

Subtask 3B: Calculation of Solid Volumes Septic Tank

The tank dimensions and measured heights of liquid, scum, and sludge taken

during inspections were subsequently used to calculate solids volumes after 6 and 12

months of accumulation time. Tables 4-9, 4-10, and 4-11 provide the scum, sludge, and

total solid volumes accumulated along with their accompanying standard deviations and

coefficients of variation.

The mean scum accumulation during the first 6-month period was 6.1 gallons,

ranging from 0 gallons (in 58 tanks) to 90.7 gallons (in 1 tank). Considering the 12-

month scum data, the mean accumulation increased to 9.4 gallons, showing that the rate

of accumulation during the latter 6 months was somewhat lower than the first 6 months;

however, care should be taken in making conclusions given the magnitude of the standard

deviations. A similar trend was observed for the sludge. The more critical time period in

terms of accumulation appears to be during the months immediately following pump out.









Why faster rates in accumulation occur in the earlier stages is not known; however, it can

be surmised that the biological community is not well established and less capable of

solid degradation soon after pump out as reported in the Bounds (1996) study. The mean

total solids volume increased after 12 months to 49.4 gallons, or 9.8% of the smallest

tank volume and 3.3% of the largest tank volume.

Table 4-9 Scum Volume 6 and 12 Months After Pump out
Accumulation Mean Standard Coefficient of
(Gallons) Deviation Variation
6 months 6.1 13.2 2.15
12 months 9.4 17.6 1.88


Table 4-10 Sludge Volume 6 and 12 Months After Pump out
Accumulation Mean Standard Coefficient of
(Gallons) Deviation Variation
6 months 28.5 24.1 0.845
12 months 41.1 29.8 0.726


Table 4-11 Total Solids Volume 6 and 12 Months After Pump out
Accumulation Mean Standard Coefficient of
(Gallons) Deviation Variation
6 months 34.3 26.7 0.779
12 months 49.4 33.2 0.673


Subtask 3C: Calculation of Accumulation Rates

The accumulation rate for scum, sludge, and total solids was calculated. The

accumulation rate for the solids was calculated for 0-6 months, 6-12 months, and 0-12

months by dividing the volume data by the appropriate time period. The accumulation

rate was also calculated on a per person basis. A linear accumulation rate per system and

a linear accumulation rate per person were determined for the first year of service, which

used the 6- and 12-month measurements. The number of people in a home, the tank









volume, and the tank capacity were evaluated to determine if these variables would affect

the accumulation rate.

Accumulation rate per system

The accumulation rate for scum, sludge, and total solids during the first six months,

second six months, and one year are presented in Tables 4-12, 4-13, and 4-14. The

accumulation rate during the second six months of service is less than the accumulation

rate during the first six months. Scum accumulation in the second six months is about

two-thirds as the first six months, while sludge accumulation in the second six months is

less than half than the first six months.

Table 4-12 Scum Accumulation Rates
Accumulation Mean Standard Coefficient of
(Gallons/Day) Deviation Variation
0-6 months 0.031 0.066 2.170
6-12 months 0.019 0.071 3.810
0-12 months 0.025 0.048 1.849


Table 4-13 Sludge Accumulation Rates
Accumulation Mean Standard Coefficient of
(Gallons/day) Deviation Variation
0-6 months 0.141 0.121 0.86
6-12 months 0.072 0.120 1.82
0-12 months 0.109 0.078 0.70


Table 4-14 Total Solids Accumulation Rates
Accumulation Mean Standard Coefficient of
(Gallons/day) Deviation Variation
0-6 months 0.171 0.134 0.791
6-12 months 0.091 0.137 1.621
0-12 months 0.134 0.086 0.670

The accumulation rates of the measured solids during the first year determined by

linear regression are presented in Table 4-15. Compared to the "rise over run" method









used to calculate the data in Tables 4-11, 4-12, and 4-13, these values are quite similar

with relatively large R2 values (a measure of goodness of fit).

Table 4-15 Scum and Sludge Accumulation Rate Data Determined Using Linear Fits
Accumulation Standard Coefficient of R2
(Gallons/day) Slope Deviation Variation Mean
Scum 0.011 0.020 1.818 0.564
Sludge 0.116 0.082 0.707 0.825
Total Solids 0.142 0.089 0.627 0.853

Accumulation rate per person

The accumulation rates for the solids were also normalized on a per person basis

for each time interval, and these values are presented in Tables 4-16, 4-17, and 4-18.

Table 4-19 presents the accumulation rates determined using linear fits and normalized

on a per person basis.

Table 4-16 Scum per Person Accumulation Rate
Accumulation Mean Standard Coefficient of
(Gallons/day/capita) Deviation Variation
0-6 months 0.010 0.020 1.978
6-12 months 0.007 0.026 3.735
0-12 months 0.009 0.016 1.909


Table 4-17 Sludge per Person Accumulation Rate
Accumulation Mean Standard Coefficient of
(Gallons/day/capita) Deviation Variation
0-6 months 0.062 0.055 0.883
6-12 months 0.032 0.058 1.967
0-12 months 0.048 0.039 0.835


Table 4-18 Total Solids per Person Accumulation Rate
Accumulation Mean Standard Coefficient of
(Gallons/day/capita) Deviation Variation
0-6 months 0.072 0.056 0.778
6-12 months 0.039 0.062 1.706
12 months 0.057 0.040 0.723









Table 4-19 Accumulation Rates of Solids per Person Determined Using Linear Fits
Accumulation Standard Coefficient of R2
(Gallons/day/capita) Slope Deviation Variation Mean
Scum 0.004 0.007 1.817 0.562
Sludge 0.050 0.040 0.791 0.825
Total Solids 0.060 0.040 1.024 0.853


Subtask 3D: Trends in Accumulation

Accumulation trends during the first year

The accumulation trends were evaluated by comparing the change in solid

volumes during the first and last 6-month periods. Table 4-20 provides the number of

systems that showed an increase, decrease, or no change in scum and sludge volumes

from the first to the last 6-month period, and Table 4-21 shows the number of systems in

which the accumulation rate changed from the first and last 6 month periods. Volumes

that remained the same or decreased from 6 months to 12 months were considered to

have a decreasing accumulation rate, as shown in Table 4-21. Of the 140 systems that

had decreased scum accumulation rate, only 17 systems increased in scum volume after 6

months. While 145 systems experienced a decrease in sludge accumulation rate, only 71

systems experienced an increased volume. A majority of those systems with decreases in

accumulation rate did not experience an increase in the accumulation volume. The result

of this lack of accumulation after 6 months shows that the systems' accumulation rates

begin to decrease after 6 months for just over half of the participants.

Table 4-20 Solids Volume Change from 6 months to 12 months
No. of Phase 1 Systems No. of Phase 2 Systems
Scum Sludge Scum Sludge
Decrease 44 40 8 9
No Change 60 22 11 3
Increase 75 117 23 30









Table 4-21 Solids Accumulation Rate Change from 6 months to 12 months
No. of Phase 1 Systems No. of Phase 2 Systems
Scum Sludge Scum Sludge

Rate Increase 62 60 19 16
Rate Constant 117 119 23 26
or Decrease _______


Phase 1 had 18 participants and Phase 2 had 6 participants with tanks where scum

and sludge accumulation rates increased during the second 6 months compared to the first

6 months. A total of 51 participants' tanks showed a decrease in scum volume, and 44

participants' tanks had a decrease in sludge volume during the second six months. The

decreasing accumulation of solids in the first year is not likely to be caused by microbial

degradation, as it has been reported that microbial activity impacts the accumulation rates

only after two years (Bounds, 1996). Sludge settling resulting in an increase in density

may cause the decrease in sludge volume.

Accumulation trends in relation to people and septic tank volume

The linear accumulation rate at one year was analyzed based on number of people

in the home, volume of the septic tank, and septic tank capacity. The septic tank capacity

was calculated by dividing the total tank volume by the number of people in the house.

The mean and standard deviation were determined for each set of accumulation rates

within each level of number of people per home (Table 4-22), septic tank volumes (Table

4-23), and septic tank capacity (Table 4-24). The accumulation rates of scum and sludge

were plotted against the number of people, the septic tank volume, and the septic tank

capacity (Figure 4-3 to Figure 4-5, respectively).

The accumulation rates based on the number of people in the home

graphically show that the accumulation rate increases as the number of people increase









Table 4-22 Accumulation Rates Based on the Number of People in the Home

Number Standard Coefficient of
of People Solids Count Mean Deviation Variation
1 Scum 28 0.006 0.009 1.482
Sludge 28 0.073 0.054 0.741
2 Scum 107 0.016 0.036 2.345
Sludge 107 0.116 0.077 0.665
3 Scum 33 0.027 0.030 1.115
Sludge 33 0.119 0.064 0.536
4 Scum 33 0.056 0.080 1.429
Sludge 33 0.121 0.098 0.808
5 Scum 13 0.054 0.055 1.010
Sludge 13 0.103 0.060 0.577
6-10 Scum 7 0.058 0.072 1.242
Sludge 7 0.181 0.174 0.962

for both scum and sludge. The accumulation rates for both solids were statistically tested

using the t-test to determine if the accumulation rate means increased with occupants.

For the sludge accumulation rate, the accumulation rate beyond 2 or more people was

statistically the same. However, an increase in the sludge accumulation rate was

statistically significant once there was more than 1 occupant in the home. The scum

accumulation rate statistically increased for each occupant from 1 to 4 occupants in the

home. For 4 or more occupants in the home the scum accumulation rate was statistically

the same. The increase in accumulation based on number of people in the home may be a

result of a higher volume of solids entering into the septic tank.

The accumulation rate based on septic tank size graphically showed that solids

accumulation increased as the septic tank volume increased. The accumulation rates

were statistically tested using the t-test to determine if the accumulation rate means

increased with the larger volume septic tanks. The sludge accumulation rate increased

for septic tank volumes larger than 750 gallons when compared to smaller tanks. The

scum accumulation rate showed to not be statistically different for any septic tank













0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05 -


u


0 2 4 6 8 1
People per Home



Sludge Mean
Sludge Values
Linear (Sludge Values)

y = 0.0137x + 0.0764


= 1-LJ^----"-
r+^M^T8


People per Home


Figure 4-3 Accumulation Rate Trends Based on number of People in the Home A) Scum
Accumulation B) Sludge Accumulation


Table 4-23 Accumulation Rate Based on Septic Tank Volume
Tank
Volume Standard Coefficient of
(gallons) Solids Count Mean Deviation Variation
<750 Scum 6 0.012 0.020 1.654
Sludge 6 0.060 0.066 1.107
750 Scum 54 0.020 0.049 2.460
Sludge 54 0.085 0.062 0.723
900 Scum 136 0.024 0.044 1.811
Sludge 136 0.123 0.080 0.651
>900 Scum 25 0.048 0.065 1.358
Sludge 25 0.128 0.107 0.835


* Scum Mean
* Scum Values
-Linear (Scum Values)


y = 0.0112x 0.0042







70




0.4
0.35 -. Scum Mean
0.3 Scum Value
o -" -- Linear (Scum Value)
S 0.25 -


08 0.15 -
S* y = 6E-05x 0.0274
E 0.1 -
3 0 .0 5 0


400 600 800 1000 1200 1400
Septic Tank Volume (Gallons)
A

0.7
0.6 Sludge Mean
0*: Sludge Value
2 0.5 -- Linear (Sludge Value)
CO
I 0.4 -
0 y = 0.0002x 0.0757
= 0.3 -


U 0.1

0 .
400 600 800 1000 1200 1400
B Septic Tank Volume (Gallons)

Figure 4-4 Accumulation Rate Trends Based on Septic Tank Volume A) Scum
Accumulation B) Sludge Accumulation

volume. The increase of solids accumulation with respect to septic tank size is likely

retention of more solids by larger tanks than compared to smaller tanks.

The septic tank capacity was plotted to further evaluate the previous two results.

The scum accumulation trend graphically shows that, as a system increased in capacity, a

larger tank with fewer residents, the accumulation of scum decreases and sludge

accumulation has an overall decreasing pattern. The t-test was used to statistically test if

the accumulation rates decreased as septic tank capacity increased. The sludge














Table 4-24 Accumulation Rate based on Septic Tank Capacity
Tank
Capacity Standard Coefficient of
(ganons/person) Solids Count Mean Deviation Variation
<200 Scum 21 0.048 0.052 1.092
Sludge 21 0.129 0.054 0.741
201-250 Scum 27 0.058 0.084 1.447
Sludge 27 0.123 0.107 0.871
251-300 Scum 13 0.045 0.060 1.131
Sludge 13 0.102 0.059 0.584
301-350 Scum 26 0.026 0.030 1.131
Sludge 26 0.127 0.063 0.493
351-400 Scum 32 0.020 0.059 2.903
Sludge 32 0.091 0.064 0.699
451-500 Scum 70 0.014 0.021 1.524
Sludge 70 0.125 0.079 0.630
501-550 Scum 4 0.607 0.009 1.358
Sludge 4 0.137 0.097 0.702
701-750 Scum 14 0.005 0.008 1.810
Sludge 14 0.061 0.044 0.719
851-900 Scum 13 0.008 0.010 1.217
Sludge 13 0.091 0.060 0.660


accumulation rate was inconclusive. The scum accumulation rate was shown to increase

with decreasing septic tank capacities. The preliminary trends in accumulation show that

accumulation decreases when larger septic tanks and fewer people are taken into

consideration.

Task 4: Interpretation of Phase 1 and Phase 2 Model Results

Subtask 4A: Assess Sample Size

As previously described, the number of participants finally chosen for this study was

restricted to a total number that would accommodate a severely limited number of

CCDOH staff assigned to pump out and solids measurement duties. The final number of












* Scum Mean
Scum Value
- Linear (Scum Value)


0.4
0.35
0.3
0.25
0.2
-2 -2
o 0.15
0.1
0.05
0 ,
400


y = -7E-05x + (.0554
a


600 800
Septic Tank Capacity (Gallons/person)


* Sludge Mean
Sludge Value
- Linear (Sludge Value)


y = -7E-05x + 5.1394


600 800
Septic Tank Capacity (Gallons/person)


1000


1000


Figure 4-5 Accumulation Rate Trends Based on Septic Tank Capacity A) Scum
Accumulation B) Sludge Accumulation




systems studied was 221. In order to assess whether this number was significantly high

enough to represent all of the Charlotte County systems (and, therefore, produce robust,

statistically significant results), the smallest significant sample size was calculated using

the sludge and scum accumulation rates determined by linear fits. Table 4-25 presents

values of significant sample sizes for both accumulation rates, along with parameters

used to estimate these values. The tolerable error was a conservative value that accounts


I
A.


0.7

0.6

0.5

" 0.4

o 0.3

0.2

0.1

0 -
400









for the average error of each measurement by using the smallest increment of measure on

each side of the mean as the width. This average "smallest increment of measure" was

determined by taking the average gallons of solids at a quarter of an inch and dividing by

365 days calculated the average smallest increment of measure. The Z /2 term, taken

from the tabulated values (Ott and Longnecker, 2001), is the area under a normal curve

for a 95% confidence interval.

Table 4-25 Significant Sample Size Values
Significant Average
sample Standard Smallest Tolerable
Solids Size Mean deviation increment error Za/2
Scum 150 0.026 0.048 0.008 0.015 1.96
Sludge 526 0.114 0.08 0.007 0.014 1.96


The sample size used in this study of 221 systems is sufficient to provide robust

analysis of scum accumulation but falls short for sludge accumulation. Therefore, care

should be taken in interpreting this latter data. It is important to note here that there was

no freedom to add additional participants in this study. The primary reason for this lack

of freedom was the previously mentioned inability of CCDOH to perform individual

pump outs and measurements beyond the final number 221. Also, because this project

was constrained by fixed deadlines set by FDEP and CCDOH in their original agreement,

new participants could not be added once Phase 1 of the project had begun. Despite not

having a sample size significantly sufficient to warrant robust correlation of sludge

accumulation with collected performance variables, meaningful trends between the two

variable types were still discerned.









Subtask 4B: Development of Correlations

Correlations of the potential performance variables to the solids accumulation

rates were constructed to determine their influence on system performance. As

mentioned previously, the Statistical Analysis Software (SAS) was used to construct

multiple linear and linear correlations. The robustness of the correlations was initially

judged based on R2 values, where 0.7 was arbitrarily set as a cutoff value.

If a correlation between the solids accumulation rates and performance variable(s)

was not shown to have a high enough R2 value (and corresponding low p value), evidence

of influencing trends between the rates and performance variable was assessed. A

performance variable was determined to have significant influence on an accumulation

rate if the probability value (or p value) was less than 0.05. The p value is the portion of

the population that will not be included in the statistical prediction.

The MLR analysis using the scum, sludge, and total solids accumulation over 6 and

12 months did not result in correlations of statistical significance (with r-square values

greater than 0.7). However, consistent trends between the independent performance

variables and the dependent accumulation rates were observed by the correlation's p

values less than 0.05. While a p value of less than 0.1 was deemed as significant but not

statistically.

Sludge accumulation rate correlations

Excessive sludge accumulation, defined as an accumulation rate greater than 2.41 x

10-4 gallons per person per day, was impacted by the washing machine activity

(specifically machine capacity, use of a water-conserving model, detergent type, and

drainage) during the first six months. The severe sludge accumulation appeared when

using liquid detergent, a large or extra large capacity, water-conserving (front-loading)









washing machine that drains to the septic tank. The washing machine detergent, washing

machine drainage, type of water-conserving washing machine model, and the washing

machine drainage were the only factors to noticeably correlate with sludge accumulation

during the first six months. The scatter plots in Figure 4-6 show the trends for washing

machine capacity, water conserving models, washing machine detergent, and washing

machine drainage against the sludge accumulation rate at 6 months. After one year,

excessive sludge accumulation did not significantly correlate to any of the variables. The

variables, use of low-flow showerheads, and the presence of plants on the drainfield

showed trends influencing sludge accumulation, but the resulting correlations were not

statistically significant.

Scum accumulation rate correlations

Unlike what was observed with the excessive sludge accumulation, excessive scum

accumulation, defined as an accumulation greater than 4.11 x 10.5 gallons per person per

day, correlated well with some performance variables using the 12-month data but not the

6-month data. Using accumulation rates at 6 months, only the occurrence of flooding

correlated with the scum accumulation rate since the probability was less than 0.10, but

was not statistically significant since it did not have a probability of less than 0.05.

However, only 14 participants reported flooded conditions in their OSTDS area, leaving

this result in question.

Correlations between the 12-month data and performance variables showed that

garbage disposal use, washing food down the sink drain, dishwasher detergent and

washing machine capacity significantly influenced the rate of scum accumulation. The

most significant correlation was obtained with the capacity (large-to-extra-large) of

washing machine (p=0.0017). As a matter of fact, 62% of the participants with









"excessive" scum used large-to-extra-large capacity washing machines. The dishwasher

detergent type showed an influencing trend with a probability of 0.0437. Sixty-one

percent of the participants with excessive scum accumulation used liquid detergent,

compared to participants that did not have excessive scum accumulation (37% of whom

used liquid detergent). Furthermore, 43% of participants that did not have excessive

scum accumulation used powder detergent, and 28% for excessive scum accumulation.

Likewise, garbage disposal use yielded a significant correlation with the 12-month scum

accumulation rates (p=0.0245) with 74% of the participants that experienced excessive

scum accumulation regularly used their garbage disposal. Whether a participant disposed

of food scraps on their dishes before washing influenced scum accumulation (p=0.0168),

and it was found that 46.4% of those participants that experienced excessive scum

accumulation did not scrape their dishes before rinsing. When pooling Phase 2 data with

Phase 1 data, the use of low-flow showerheads was shown to decrease scum

accumulation with 68.5% of the participants that did not have excessive scum

accumulation used these showerheads. The scatter plots further illustrate the trend in

scum accumulation for these performance variables (Figure 4-7).

Solids disposal and flooding trends influenced excessive scum accumulation at 12

months, but the resulting correlations were not statistically significant. The practice of

improper solids disposal showed an influencing trend for scum accumulation (p=0.0561)

with 63% of participants that had excessive scum accumulation improperly disposed of

solids while 44.8% of participants that did not have excessive accumulation also

improperly disposed of solids. The occurrence of flooding, again, correlated with

excessive scum accumulation with a p value of 0.0711. Although, only 15.2% of









participants that had excessive scum accumulation experiencing flooding and 5.6% of

who do not have excessive scum accumulation experience flooding. The low percent

value does not seem evident in supporting the significant of flooding at 12 months.

Subtask 4C: Development of Model Results

A model was attempted for both solids at six months and at one year. At six

months, the largest R2 achievable was 0.405 using all the potential performance variables,

and the largest R2 at one year was 0.56 using all the potential performance variables. The

inability to produce a model from the data is a result of both too few data points and the

large amount of variability present in the solids measurements. The short time in which

these measurements were collected most likely is not long enough to adequately measure

system performance.







78



% 0.45 0.45




. 0.3 0.3
0. M
E 0-

S 0.15 0.15

" *


0 02
0 1 2 3 0 B 1 2
A B



S 0.45 0.45

0


0.3 0.3






C D
E. 0.15 0.15





0 1 2 3 0 1
C D








Liquid; 2 = Powder; 3 = Both) D) Washing Machine Drainage (0 = Does Not
Drain to OSTDS; 1 = Drains to OSTDS)







79


0.4 0.4

*-
e 0.3 0.3







f 0.1 0.1


0 0
0 1 2 3 1 2 3 4
A B








S 0.3 0.3
& | 0.2 0.2
























S0.1 0.1



0 0
0 1 2 3 0 1 2 3 4
0 .4 ------------| 0 .4 T-------------
















C D



Figure 4-7 Scatter Plots for Scum Accumulation Rates at 12 Months with the lines
representing the trend A) Garbage Disposal Use (0 = Not Applicable or
Never; 1 = Occasionally; 2 = After Dinner; 3 = Always) B) Food Down Sink
Drain (1 = Food is Scraped from Plates and the Sink is Strained; 2 = Food is
Scraped from Plates and the Sink is Not Strained; 3 = Food is Not Scraped
from Plates and the Sink is Strained; 4 = Food is Not Scraped from Plates and
the Sink is Not Strained) C) Dishwasher Detergent (0 = Dishwasher is Not
I I 0 .2----------- 0 .2-------------




















Used; 1 = Liquid; 2 = Powder; 3 = Both) D) Washing Machine Capacity (0 =
< 0.1 --- ; -- ^ -- 0.1---------- ^

















No Washing Machine; 1 Compact; 2 Medium; 3 Large; 4 Extra

Large)
Large)














CHAPTER 5
SUMMARY AND CONCLUSIONS

The primary goals of this project were to determine what characteristics of

household activities, system design, and environmental conditions impact the

performance of OSTDSs to a significant extent and to provide CCDOH with a list of

recommended changes to current practices in OSTDS management by Charlotte County

residents. A secondary goal was to develop a model to allow prediction of solids

accumulation over time. In order to achieve these goals, data on current OSTDS

practices, systems, and environmental conditions were obtained by means of surveys,

existing state/county documentation, and inspections, and then evaluated against the

accumulation rate determined from measurements taken at 6 and 12 months.

The budget and time restrictions limited the sample size to be 300 or less

participants. Although, extreme efforts were taken to recruit OSTDS using homeowners,

only 221 residents were willing and qualified to participate. All data collected through

out the study were databased to maintain the data, while being able to be easily converted

into a useable format for statistical analysis.

The solids measurements at 6 and 12 months from pump out were converted into

sludge and scum volumes using the specific septic tank dimensions. The accumulation

rates were calculated using the number of days between measurements, and the

accumulation rates were determined with linear fits to take into account for the change in

the accumulation rate through out the year.









In order to best determine the that characteristics of household activity, system

design, and environmental conditions impact on the accumulation rates, the performance

variables were linearly correlated against the accumulation rates. The linear correlation

between the accumulation rate and a specific performance variable assesses the

relationship between the two. The performance variables that correlate to the

accumulation rates were used to develop a model for predicting the accumulation rates.

Before a model is created, the performance variables were related to the accumulation

rate using multiple linear correlations. An R2 value is determined for that multiple linear

correlation, when the R2 value is less than 0.7 a significant model cannot be predicted

using only these performance variables.

The resulting conclusions at one year are that scum and sludge accumulation was

too random to be used in creating an accumulation model for predicting pump out

frequencies. Trends in sludge accumulation proved to be ineffectively significant with

the inadequate sample size. The number of participants for scum accumulation trends

was significant enough.

Scum accumulation rates showed to be impacted by wastewater quality and

hydraulic characteristics than system design and environmental conditions. During

correlations with the performance variables, the scum accumulation rate at 12 months

significantly related to the frequent use of garbage disposals, allowing food particles to be

disposed of down the sink drain, the washing machine capacity, and the dishwasher

detergent.. Sludge accumulation did not have an adequate sample size, resulting in an

inconclusive statistical analysis.









While some potential variables were significant in the study, other performance

variables were not, possibly because of the short measurement period of one year may

not provided enough time to completely characterize system performance. Previous

studies used a time period of up to eight years. The increase of solids accumulation

during the last six months showed that for these systems the maximum accumulation rate

in these systems did not occur within the first year of service. While not completely

understood, the cause of the drastic decrease in solids volumes from six to 12 months of

service was possibly caused by system failure, unexpected early microbial activity, or

settling of stored solids, resulting in a denser sludge blanket.

The variables that significantly impacted accumulation rates of scum and sludge are

the following:

* Washing machine capacity;
* Garbage disposal use;
* Low-flow showerheads;
* Direct disposal of food particles;
* Washing machine detergent;
* Water-conserving washing machine model;
* Flooding.

Given the trends observed with the above-mentioned household activities, the following

practices are recommended to ensure optimal performance of OSTDSs in Charlotte

County:

* Promote use of water-conserving fixtures and appliances;
* Discourage the use of unnecessary over-sized capacity washing machines;
* Limit garbage disposal use to extend the pump-out interval;
* Encourage occupants to limit the amount of solids and foods particles that exit
through the drain and enter the septic tank;
* Promote unsaturated soil conditions to prevent high ground water levels from
infiltrating into the septic tank via the drainfield or leaky tank.









The results of this study have potential to significantly impact the public health of

Charlotte County residents by ensuring prevention of pollution from OSTDSs into its

numerous water bodies. Providing information concerning the effects of certain

household activities on system performance to OSTDS owners would result in a

heightened awareness of the impact of their activities not only on their system behavior

(and frequency of pump-outs) but also on the health of the surrounding environment.

Given that the literature has reported that the majority of system owners are unaware of

these connections and that many of the participants polled in this study were also

unaware of appropriate maintenance procedures, transfer of this information to the public

is imperative.














CHAPTER 6
RECOMMENDATIONS FOR FUTURE WORK

The work performed in this study is vital for the improvement of management and

maintenance for OSTDSs. Further analysis of accumulation rates will help lead the

progress for OSTDS management and ultimately, public and environment health. The

purpose of this chapter is to provide recommendations for future studies that may attempt

to extend this project or repeat the methods reported herein. The results and conclusions

brought forth from this study show that data collection is among the most important

aspect for the analysis of solids accumulation. A majority of the recommendations to

follow will discuss the importance of various aspects of sample size, monitoring of

accumulation, and collection of performance variables collected.

Identification of Relevant Variables

In this study, three major groupings were used to identify potential performance

variables. In identifying variables for this study, anything that could possibly impact a

accumulation was gathered, thus resulting in a large set of independent variables with

unknown links to wastewater generation. Additional research of each variable and its

possible relationship to wastewater generation may have provided more informaed

insight in development of survey questions. An example of this in this study is garbage

disposal use. Given that a closer study of the variability that exist in use of garbage

disposals, the different levels of use (never, occasionally, only after meals, and always)

could have been more accurately defined. In doing so, the survey questions could have









been better posed to elicit more accurate responses and, ultimately, more robust

correlations.

Selection, Recruitment, and Monitoring of Participants

Other factors to consider in studies such as these include the ability to monitor

solids accumulation over the entire pump out interval and to obtain a significant sample

size. Monitoring over the entire pump out interval will create a model that describes the

accumulation that determines the need to perform maintenance pumping. An adequate

sample size will ensure that the statistical analysis performed will bring forth more

meaningful results. The sample size needed for this study over one year was 150

participants for scum accumulation and 526 participants for sludge accumulation.

However, it is important to remember that the sample size required could change for

different monitoring periods.

Participant Selection

The participants used in an accumulation rate study should be selected on the basis

of soil type, tank size, and number of occupants. Selecting participants based on the

designated soil type is viable if it is possible to recruit strictly from the desired soil types.

Participant selection should use a nested design based on number of people in the home

and the septic tank size. (Further information on nested design can be found in statistical

experimental design textbooks.) Participants should have available septic tank

manufacture and dimensions with no current failures.

Recruiting Participants

The most successful recruitment technique was the booth at the county fair. The

booth allows initial questions to be answered that would otherwise inhibit residents from

participating. If mailing is desired, using a two-part postcard that can be mailed and a









portion of it returned that is sent to every potential participant in the desired area is

recommended. A two-part postcard would allow the study to be introduced to the

prospective participants, and the returned portion can provide information on the number

of occupants, contact information, and other information needed before collecting

performance variable data. The two-part postcard would save both time and money

(especially since survey packets would only be sent to interested recruits).

Division of Recruits for Two Groups

Maintaining two groups, one for creating a predictive model and the second for

validating the model, is recommended. Using the nested design discussed above would

prevent the need to separate the recruits, since the recruits would be placed into the

appropriate model, and the tank volume and number of occupants would be used in

selection and separating the recruits.

Data Collection

The potential performance variables were collected by means of surveys, permits,

and inspections. The use of surveys was essential for collecting the household activities

variables, which were mailed to the participant. Most of the participants mailed the

surveys back promptly but many of the participants did not, leading to phone calls or

having the participants complete the survey during an inspection.

Monitoring solids accumulation was performed for one year in 6-month intervals. It

is recommended to monitor systems for the entire pump-out interval after the septic tank

is pumped. Having a longer interval between monitoring would allow enough time for

more participants to be included. The changes in accumulation observed in this study

lead to the recommendation that monitoring intervals do not exceed 1 year.






87


Calculation of Solids Accumulation and Model Development

The calculation of solids accumulation is performed in several steps, tank

dimension collection, volume calculation, and accumulation rate calculation. Selecting

participants based on having known septic tank dimensions, if possible, would prevent

the introduction of error incurred from calculating tank dimensions. It is also

recommended that the investigators have or receive sufficient training in statistics prior to

the modeling phase to ensure that all considerations have been made prior to and during

analysis.