Radon information system for new house construction

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Radon information system for new house construction
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Li, Win-Gine
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Thesis (Ph. D.)--University of Florida, 1995.
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Includes bibliographical references (leaves 207-214).
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by Win- Gine Li.
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Typescript.
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Vita.

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University of Florida
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RADON INFORMATION SYSTEM FOR NEW HOUSE CONSTRUCTION


By



WIN-GINE LI













A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORIDA


1995





























To my parents and in memory of my younger brother















ACKNOWLEDGMENTS

This work was sponsored by the Florida Department of

Community Affairs, whose funding is sincerely appreciated. I

wish to thank the colleagues who worked on the project with

me. Special thanks are due to Dr. David Hintenlang, Mr.

Kaiss Al-Ahmady and Mrs. Huong Iselin from the Department of

Nuclear Engineering and Sciences for their support and

encouragement.

I would like to express my sincere thanks to Dr. Fazil

T. Najafi, the committee chairman, for his compassionate

guidance and patience in making this study possible. I

sincerely thank Dr. Paul Thompson, Dr. Mang Tia, Dr. John

Staudhammer and Dr. Elroy Bolduc for serving as my committee

members. I thank them for taking their precious time in

helping me complete this work.

My family has supported me so much for more than six

years from thousands of miles away. Their love and

encouragement have motivated me to complete this work. I

deeply appreciate their sacrifices and support both

financially and spiritually.

My host parents, Rachel and Scott Gray, have given me

much love during my stay in the United States. I would like

to thank the Lord for His everlasting love to make this work

possible. Also, Dr. Fadi Nassar, Mr. Xiaoyu Fu, Mr. Quan-


iii








Yang Yao, Dr. Wei-Tong Chen, Mr. Bill Epstein, Ms. Candance

Leggett, Ms. Irene Scarso, and all my friends whose

consideration and support have made me feel comfortable far

from home.
















TABLE OF CONTENTS


ACKNOWLEDGMENTS .............................


iii

. ix


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

LIST OF FIGURES ..............


.... xi


ABSTRACT ............. ........................ ............. vxi

CHAPTER


1 INTRODUCTION ................
Research Overview ..........
Statement of Problem.......
Radon Information Is Not
Accessible ..............
Objective of Work ..........
Scope of Work ..............
Description of Chapters ....


Well


Organized


2 RADON RISK IN HEALTH AND ITS CAUSES.
Introduction. .......................
What Is Radon?........................
Potential Radon Exposure Risks ......
Chronological Studies and Statements
Radon and Liability ...............
Radon Decay Chain ...................
Radon Damage Mechanism..............
Radon Measurement Units ..........
Radon Concentration ............
Radon Progeny...................


Radon


Radioactive Decay.


.................................. 22


Decay Relationship between Parent and Daughter.
Summary. .............................................

3 RADON TRANSPORT IN STRUCTURES .......................
Introduction.........................................
Review of Literature ...............................
Research Subjects....................................
Sources that Contribute to Indoor Radon .............


and


Risks


. 7
S7
S7

10
15
16
18
. 20
20
21


... 23
... 25









Radon Transport in Substructures ....................... 29
Radon in Soil and Its Movement ...................... 29
Radon Emanation Coefficients ........................ 31
Indoor Radon Prediction Model ....................... 32
Soil Permeability ................................... 33
Radon Flows Through Different Soil Layers ........... 38
A Proposed Mitigation Method ........................ 40
Soil Permeability in Different Depths ............... 40
Radon from Geological Consideration ................. 42
Geological Elevated Radon Summary ................... 43
A Generalized Geological Map for the State of
Florida ........................................... 45
Phosphate Region and Indoor Radon Levels in
Florida................................ ............ 50
Summary of Radon Transport in Substructures............. 50
Radon Transport in Superstructures ..................... 50
Radon Transport through Concrete Floor Slab ......... 53
House Water ............... .......................... 55
Emanation from Building Materials ................... 56
House Ventilation ................................... 58
Ventilation Rates and Indoor Radon Concentrations ... 59
Radon Entry Rate .................................... 59
Pressure-driven Flow ................................ 64
Summary of Radon Transport in Superstructures .......... 68

4 ANALYSIS OF HOUSE RADON AND CRACK STUDY................ 71
Introduction ........................................... 71
House Physical Characteristics and Soil Radon .......... 71
Soil Data Analysis ..................................... 75
Crack Study............................................ 77
Crack Research Process .............................. 78
Data Analysis ....................................... 79
Correlation Analysis ............................... 81
Calculation of Crack Parameters ..................... 84
Comparison of Crack Characteristics with Indoor
Radon ............................................. 84
Potential Crack Radon Entry Analysis ................ 84
Crack Resistance Analysis ............................ 88
Crack Study Summary..................................... 90
Infiltration and Indoor Radon Test Results ............. 91
Two Radon Research Experiments ......................... 95
Effectiveness of Tube Length on the Measurement of
Radon Concentration ............................... 97
Equipment Used ..................................... 97
Testing Procedures ................................ 97









Site Selection and Testing ......................... 98
Test Results....................................... 98
Discussion of the Experiment ........................ 01
Indoor Radon Concentration Variation Due to
Pressurization .............................. ...... 102
Objective of the Experiment ...................... 102
Experimental Procedure ............................. 102
Experimental Results. ............................ 103
Discussion of the Experiment ....................... 103
Summary. ................................ 105

5 CONSTRUCTION METHODS ............ ..... ..... .............. 106
Introduction ............................................ 106
State-Of-The-Art Construction Mitigation Methods...... 106
Enkavent Mat Method................................... 107
Installation Procedures .......................... 108
Suction Pit Method.................................... 108
Perforated Pipe Method................................. 111
Mechanical Barrier.................................... 111
Change of Foundation Soil ............................. 115
Fill Materials or Layered Natural Soils ............ 116
Construction Materials ............................ 117
Costs Comparisons ..................................... 118
Planned Mechanical Systems ............................ 118
A New Radon Mitigation Method........................... 121
Summary ............................................... 123

6 ESTABLISHMENT OF KNOWLEDGE BASE........................ 124
Introduction ............. .............................. 124
Effective Information Retrieving ...................... 125
Expert System Applications............................ 125
Advantages of Managing Radon Information by Expert
Systems ....... ................................... 125
Performance Improvement and Knowledge Transferring
through Expert Systems .............................. .126
The Structure of Knowledge-Based Expert Systems .... 127
Objective of the Knowledge Base Development ............ 129
Knowledge Acquisition .................................. 130
Selection of Knowledge Domain ....................... 130
Control Mechanism of This System....................... 132
Database Development .................................. 132
Identify Target Users .............................. 133
Establish Problem Boundaries ....................... 133
Obtain Expert Support .............................. 135
Organize the Facts from the Knowledge Databases ....... 135


vii










Design Rules .......................................
System Development. ....................................
Homeowner Database .................................
Contractor Database ................................
Researcher Database ................................
Sample Applications of the Expert System ...........
System Testing and Validation .........................
Summary. ...............................................

7 CONCLUSION AND RECOMMENDATIONS ........................
Summary and Conclusion..................................
Effectiveness of the Radon Mitigation Methods .........
Cost-Effectiveness of the Mitigation Systems ..........
Advantages of Radon Information System ................
Recommendations .......................................
Author's Contribution to the Advancement of Radon


Knowledge ................................


.......... 161


APPENDICES


A STATISTICS PROGRAMS ........................
Testing Equality of Four ACH Experiments...
Indoor Radon and Its Correlation Tests ..
Sample Program Output: Normality ........
Sample Program Output: Correlation ......
B HYPERTALK PROGRAMS .........................
HyperTalk Scripts ..........................
C EXAMPLE OF KNOWLEDGE BASE ..................
Crack Sealant Knowledge Base ...............
Crack Treatment Knowledge Base .............
Indoor Radon Prediction Knowledge Base.....


163
163
166
167
169
170
170
192
192
195
203


LIST OF REFERENCES ...................................... 207

BIOGRAPHICAL SKETCH ..................................... 215


viii


137
139
139
143
145
149
156
157

159
159
159
160
160
161


. ...

. ,. .
. .. .
o
. o o. .
. ... .
. . .
. ... o. .















LIST OF TABLES


Table ................... ................. .. ........... acge

2.1 Organ Dose Ratios and Absolute Risk .................. 9

2.2 Major Radon Studies and Statements .................... 12

2.3 Radon Isotopes and Their Half-lives .................. 19

2.4 Properties of Radon Progeny ........................... 19

2.5 Definition of Working Level ........................... 21

3.1 Soil Permeability .................................... 37

3.2 Utilization and Costs of Water Radon Mitigation
Methods .................. ............................. 57

3.3 Radon Emanation Rates ................................ 58

3.4 House Radon Entry Data ............................... 65

4.1 House Characteristics (Project of 1992) .............. 72

4.2 Radon Test Results (Project of 1992) ................. 73

4.3 House Characteristics (Project of 1993) .............. 74

4.4 Radon Test Results(Project of 1993) .................. 75

4.5 Crack Classification ............... ..................... 78

4.6 House Characteristics ................................ 82

4.7 House Basic Statistics in the Crack Study ............ 83

4.8 Correlations between Factors ......................... 83

4.9 Crack Resistance in Three Projects ................... 90

4.10 Infiltration Rate and Indoor Radon Concentration.. ..93








4.11 Multiple Comparison of Means ........................ 94

4.12 Tube Lengths and Their Calculated Radon Readings
(0-25 ft) .................. .......................... 99

4.13 Tube Lengths and Their Calculated Radon Readings
(25-50 ft) .. ........................................ 100

5.1 Soil Changing Analysis ............................... 116

5.2 Costs of the Enkavent Mat System ..................... 119

5.3 Costs of the Suction Pit System ...................... 120

6.1 Radon Index Matrix ................................... 146

6.2 Probable Indoor Radon Level ............................ 147

6.3 Decision Table of the Indoor Radon Prediction ......158












LIST OF FIGURES

Figure ................................................ -

2.1 Radon Gas Damage Mechanism ............................ 8

2.2 Decay Flow Chart of Uranium .......................... 17

3.1 Major Research Subjects. ............................. 28

3.2 Soil Gas Radon Entry Mechanism and Affecting
Parameters .................................. ...........30

3.3 Effect of Moisture Content on the Relative Radon
Emanation Coefficient [Nazaroff 1992]. .............. 32

3.4 Indoor Radon Prediction by Using Soil Radon .......... 34

3.5 Soil Gas Radon Mitigation by Perforated Pipe
Systems .............................................. 41

3.6 Permeability Distribution of Different Pressure. .....42

3.7 Average Indoor Radon Levels vs. Soil Radon
Concentrations ..................................... .44

3.8 Average Indoor Radon Concentration vs. Soil Radon
Concentration ...................................... .44

3.9 Generalized Geology Map of Florida [Otton 1993]. ......46

3.10 Generalized Surface Materials Map for the State of
Florida [Otton 1993] ................................ 49

3.11 Phosphate Distribution in Florida [Roessler et al.
1983] ................ .............................. 51

3.12 Indoor Radon Levels of Florida [DCA 1994] ........... 52

3.13 Indoor Radon vs. House Ventilation Rate. ............ 60

3.14 Radon Entry Rate for House "Robin Lane" .............. 62

3.15 Radon Entry Rate for House "Summit Oaks" ............ 63









3.16 Across Slab Differential Pressure for House
"Summit Oaks". ...................................... 69

3.17 Across Slab Differential Pressure for House "Robin
Lane" ................... ............................ 70

4.1 Distribution of Indoor Radon versus Subslab Radon. ...76

4.2 Indoor Radon versus Subslab Radon. ................... 77

4.3 Crack Map of House "Summit Oaks" ..................... 80

4.4 Calculation of Total Crack Equivalent Area............85

4.5 Average Subslab Radon and Indoor Radon
Concentration ................... .................... 86

4.6 Indoor Radon/Subslab Radon vs. Total Equivalent
Crack Area. ................... ...................... 86

4.7 Crack Resistances of the Houses Tested. .............. 89

4.8 Indoor Radon Levels vs. Infiltration Rates. ...........96

4.9 Correlation between Indoor Radon and Infiltration
Rates ................... ............................ 96

4.10 Tube Lengths and Their Radon Readings. .............. 101

4.11 Radon Concentrations with Respect to Pressure
Changes ................... .......................... 104

5.1 Enkavent Mat Placement. .............................. 109

5.2 Typical Enkavent Mat Layouts. .......................... 110

5.3 Suction Pit Placement ................................ 112

5.4 Mechanical Barrier. .................................. 114

5.5 Solid Concrete Block Barrier and Vapor Barrier
Installation Layout. ............................... 117

5.6 A Schematic Illustrating the Application of an
Electrially Induced Soil-Gas Barrier. ................122

6.1 The Basic Structure of a Knowledge-based Expert
System ................... ........................... 128


xii








6.2 Knowledge Base Expert System Establishment
Procedures ................... ....................... 131

6.3 Schematic Diagram of the Interface System. ........... 133

6.4 Hierarchical Structure of HyperCard. .................. 138

6.5 Entity Relationship Diagram of Hypercard Elements. ...138

6.6 Data Transferring Between Stacks. .................... 139

6.7 Illustration of System Menu. .......................... 141

6.8 Key Elements of Homeowner Database .................. 141

6.9 Hierarchical Flow Chart of Homeowner Database. .......142

6.10 Key Elements of Contractor Database .................144

6.11 Program Output of Radon Index. ...................... 147

6.12 Functions of Mitigation Methods Database. ........... 148

6.13 Key Elements of Researcher Database. ................ 148

6.14 Linkage of Hypercard and MacSmarts Expert System. ...150

6.15 Expert System Output (crack.fig.lb) for Crack
Treatments. ........................................ 152


xiii















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


RADON INFORMATION SYSTEM FOR NEW HOUSE CONSTRUCTION

By

Win-Gine Li

May, 1995





Chairman: Dr. F. T. Najafi
Major Department: Civil Engineering


Exposure to a high level of radon gas has been found to

be a health threat. Researchers have concentrated on

investigating the factors that affect radon entry and to

designing mitigation methods in preventing radon intrusion.

This research focused on radon gas prevention in new

residential houses. Subjects related to house structures

were thoroughly examined from substructures to

superstructures. The major factors in the substructures

investigated are soil type, soil moisture content, soil

permeability, soil radium content, and geology, while in

superstructures the factors investigated are concrete slab

characteristics, floor cracks, types of building material,


xiv








house water, house ventilation, and pressure differentials.

Based on the results of the University of Florida research

projects, the data were analyzed. Correlations between

various factors that might have an effect on radon entry

were analyzed statistically. The parameters include soil

radon, subslab radon, floor cracks and foundation type. In

addition, the precision of radon measurements was discussed.

The results have shown that the radon mitigation systems

have successfully brought down indoor radon levels below the

U.S. Environmental Protection Agency's standard.

Recent construction mitigation methods were reviewed.

The methods are mostly based on the projects of the

University of Florida and the U.S. Environmental Protection

Agency. The installation procedures, materials used and

costs of suction pit and Enkavent mat methods were all

detailed in the content. A computer-aided design, Radon

Information System, has been developed for use in

construction for preventing radon intrusion. Procedures and

materials used for constructing a radon resistant house were

incorporated in the system. Radon Information System was

developed for diagnosing radon problems and providing

information available upon request. The system provides

object-oriented databases in conjunction with an expert

system to deal with radon problems. Final conclusion about

the effectiveness of the radon mitigation methods and

suggestions for future research subjects were described.















CHAPTER 1
INTRODUCTION


Research Overview


This chapter provides an overview of the entire

research, describes the principal problem, and reveals the

reasons this research is needed. A historical review of

previous research and a brief introduction of each chapter

are also presented.



Statement of Problem


Radon is a radioactive gas which occurs in nature and

can not be seen, smelled or tasted. Radon can be found in

soils, and it can migrate through foundation slabs and enter

houses. In an enclosed space, radon can accumulate. The risk

of developing lung cancer from exposure to radon depends

upon the concentration of radon and the length of time

people are exposed. In general, the risk increases as the

level of radon and the length of exposure increase. The U.S.

Environmental Protection Agency (EPA) estimated that radon

gas is responsible for 5,000 to 20,000 deaths annually in

the United States. Although this is a large number, it

represents less than 10% of total lung cancer deaths and








only 2% of all cancer deaths [Bodansky et al. 1987]. Based

on the available information, the U.S. EPA suggests that

homes with levels above 4 pCi/L (picocuries/liter) are

harmful to human beings [EPA 1986].

The soil is the primary source of indoor radon in

single-family houses in the United States [Nero and Nazaroff

1984]. Pressure-driven flow is a principal means by which

soil gas enters houses; it is expected to be the predominant

source of radon in houses with elevated concentration

[Garbesi and Sextro 19891].

Since radon can migrate from soil through the slab, we

should consider methods to prevent radon entry into houses

while planning to build a new house. Some techniques have

actually been applied during the construction of new houses.

The applicability, cost feasibility, radon-prevention

effectiveness, and durability of the techniques cannot be

fairly assessed. The EPA-sponsored radon prevention projects

in new house construction should provide a better evaluation

of radon prevention alternatives.

The University of Florida (UF) has received research

funds from the Department of Community Affairs (DCA) to

evaluate the effectiveness of potential building design and

construction criteria. The results will be used to reduce

radon entry into new houses and to develop recommendations

based on the evaluation for future improvement. Fourteen

houses were constructed according to Draft Standard for

Radon Resistant Building Construction in 1992 and twelve








houses in 1993. The data sets were analyzed statistically by

the SAS program. However, the research results from the

prior studies were not organized in a way that people could

access them easily.


Radon Information Is Not Well Organized or Accessible


There have been many research projects on radon

problems. Research results have been published in journals

and conference proceedings. However, the radon knowledge

has not stored or organized properly. If these research

findings and the ongoing projects' findings were saved on a

computer, people could share them more easily. In addition,

these facts could be transformed into a knowledge base which

could be utilized to aid in decision making. Therefore,

radon information should be saved on effective computer

programs that will benefit users financially and timely.



Objective of Work


Based on the investigation of previous research

findings and the UF project results, the Radon Information

System (RIS) was developed. It is designed to assist radon

information retrieval, consulting and problem diagnosis.

Also, RIS emphasizes on radon resistant construction methods

for preventing radon intrusion.

Object-oriented databases in conjunction with an expert

system were established in RIS. The databases were based on








intensive experiments from previous research and the

Environmental Protection Agency's methods and standards. New

house construction regulations, procedures, scheduling, cost

estimation, and materials used were included in the system.

Graphical construction procedures of mitigation systems and

a potential radon index were also incorporated into the

system. The user-friendly RIS is capable of assisting

builders, contractors, homeowners, and researchers in

obtaining suggested information for decision making.


Scope of Work


A literature review was conducted on methods of

constructing of radon resistant houses. The information was

then transferred into computer knowledge bases. The review

focused on the construction methods used for preventing

radon intrusion. Previous work reviewed consisted of radon

sources and radon movement in soil, house ventilation rates

and pressure differentials from indoor to sublsab. Recent

work reviewed consisted of evaluation of the efficiency of

improved slab construction, construction costs, crack study,

house ventilation rates, pressure differentials from indoor

to sublsab, and subslab depressurization systems. The

results of the various investigations were compared to

similar research in the past to investigate the cause and

effect relationship between building characteristics and

radon entry. The collected data from the literature were

analyzed statistically. The results of this investigation








and findings from previous research were incorporated into

computer knowledge bases. In addition to literature review,

the following experimental work were conducted: floor crack

study, pressure differentials tests, and tube length effect

on radon reading tests.



Outline of Chapters


Chapter 1 through Chapter 3 are the background

information of radon from previous research findings. These

findings are precious because they give guidelines and

comparisons for the recent research. Chapter 4 is the

analysis of UF research results. Chapter 5 describes the

most recent mitigation methods. Based on Chapter 1 through

Chapter 5, the important findings and necessary information

are transformed into computer programs and are described in

Chapter 6. A brief description of each chapter is as

follows:

Chapter 1 is the overview of the whole research.

Chapter 2 discusses the radon risks in health and its causes

and sources. The definition of radon measurement units,

radon prevention events, radon decay chain and radon entry

mechanism that affect radon entry are discussed.

Radon entry related subjects in substructures (from

slab to soil) and superstructures (from slab and above) are

all detailed in Chapter 3. Important subjects in

substructure include soil radium content, soil permeability,

and soil moisture content. Slab cracks, building materials,








housing water and indoor radon are the key subjects in

superstructures.

Chapter 4 discusses the data obtained from New House

Evaluation Program (NHEP) research projects. The data were

analyzed statistically. In addition, two experiments,

effectiveness of tube length on radon readings and pressure

changes on radon concentrations, are discussed.

The up-to-date construction methods in preventing radon

intrusion are introduced in Chapter 5. Subslab

depressurization methods are all detailed in steps.

Chapter 6 discusses the applications of computer aided

design for radon knowledge consultation. A radon information

system is developed for assistance in radon problems.

Chapter 7 contains the conclusions and recommendations

for future research.















CHAPTER 2
RADON RISK IN HEALTH AND ITS CAUSES


Introduction

People exposed to high radon concentration will most

likely get lung cancer. The potential risk of exposure is

discussed in this chapter. The position of the governmental

agencies toward radon assessment is outlined. The cause of

radon damage is also introduced.



What Is Radon?

Radon (Rn-222) is the decay product of uranium. It is a

radioactive, odorless, colorless, and naturally-occurring

gas. It can contribute to significant damage to respiratory

tissue when there is prolonged exposure to elevated

concentrations of the gas. Constant exposure to high

concentration of radon gas may cause lung cancer. Figure 2.1

illustrates the mechanism of radon damage to lung tissues.



Potential Radon Exposure Risks

The significance of the estimated health effects from

radon daughter exposure to the bronchial epithelium is

7



























Lungs

Figure 2.1 Radon Gas Damage Mechanism


compared to the corresponding health effects to other parts

of the body. The proportional dose to other organs can be

estimated by first considering the ratio of bronchial

epithelium dose to alveolar dose. Table 2.1 shows the

relative dose to each organ in comparison with the dose to

the critical tissue, which consists of the basal cells of

the bronchial epithelium. Dose to this tissue is often

referred to as the tracheo-bronchial or T-B dose, according

to the International Commission on Radiological Protection's

(ICRP) respiratory tract model. The proportional doses to

other organs are given as fractions of the T-B dose, for the

condition where the body is in equilibrium with the radon









containing atmosphere. The T-B dose effect or risk of

concern from radon daughter exposure is lung carcinoma.

Since lung cancer has such a high mortality rate, it is

assumed that morbidity for this dose effect is equivalent to

mortality. Morbidity does not equal mortality for the

corresponding dose to other organs. However, the relative

doses to other organs are insignificant when added to the

risk from T-B dose [Johnson 1973, p.31-33].

Table 2.1 Organ Dose Ratios and Absolute Risk
Organ to T-B

Organ dose ratio1


Bronchial epithelium 1.0000

Alveoli 0.0291

Liver 0.0013

Gonads 0.0009

Bone 0.0005

Bone marrow 0.0011

Kidneys 0.0066

Blood 0.0026

Muscle (soft tissue) 0.0007


Modified from [Johnson 1973, Table 8]


1 Ratio of organ dose to T-B dose for conditions where the body is in
equilibrium with the radon containing atmosphere.









Viel observed a statistically significant positive

correlation between myeloid leukaemia mortality in adults

(AML) and radon exposure [Eatough and Henshaw 1994]. This

positive correlation with radon exposure is in agreement

with similar observations at country level for AML in

England and Wales for myeloid leukaemia in England. Radon

as a risk factor for tumors, melanoma and kidney cancer is

unclear. Further studies are needed to determine the radon

risks.



Chronological Studies and Statements of Radon Risks

The radon problem did not received serious attention

until the early 1980s. Radon gas is one of the most

dangerous environmental pollutants. Radon risks have been

reviewed by the Agency for Toxic Substances and Disease

Registry, the Centers for Disease Control, the EPA, EPA's

independent Science Advisory Board, the International

Commission on Radiological Protection (ICRP), the National

Academy of Sciences (NAS), the National Cancer Institute

(NCI), the National Institute for Occupational Safety and

Health (NIOSH) and the Surgeon General (SG). Each of these

parties have reached consistent conclusions about the health








threat of radon exposure [HR 1994, p.12]. A chronology of

major events is listed in Table 2.2.

The United States General Accounting Office (GAO) had

testimony on the radon contamination reduction in houses in

1988. The testimony concluded that federal agencies involved

with housing have responded differently to radon hazards.

The overall federal housing response to the radon problem

has been fragmented and been on small scale. The Congress

should bring greater attention to the radon problem and

order federal agencies to take more responsibilities about

the radon issue [GAO 1988].

A hearing was held in 1990 on federal efforts to

promote radon testing. This hearing provided a closer look

at the radon problem and directed the funding and research

guidelines [HR 1990]. The House Representative bill (HR)

2448 amends Title III, "Indoor Radon Abatement", of the

Toxic Substances Control Act (ASCA). It requires the EPA

Administrator to establish a mandatory performance and

proficiency program for radon products and services [HR

1993, p.45]. The Administrator will make available to the

public a list of those measurements and mitigation products

which have met minimum performance criteria. In addition, it











Table 2.2 Major Radon Studies and Statements
Year Agent Statements

1986 EPA 1. Released "Citizen's Guide" on

Radon.

2. Estimated 5,000 to 20,000 deaths

annually. Action Level of 4 pCi/L.

1987 ICRP ICRP report concluded that radon poses

a greater cancer risk than assumed by

EPA.

NIOSH Reported "significant health risks".

Occupational standard: 1 WLM/year2.

1988 NAS 1. NAS report (BIER IV) found greater

risks than previously assumed by EPA.

2. Based on miners studies, estimated

potential lung cancer risk.

3. Recognized the difference between

mining and domestic environment:

remains unsolved.

EPA A new estimate of 8,000 to 43,00

deaths annually. Averaged 21,600

deaths.

SG Issues "A national health problem"

that estimates thousands of deaths

each year.


2 One Working Level Month (WLM) per year is approximately equivalent to
4 pCi/L.








Table 2.2 Continued

Year Agent Statements
1991 NAS Based on a comparison between mines and

homes, estimates 30% reduction in homes
compared to the first report.
EPA Completed national residential radon survey.

Revised its estimate from 1.29 to 1.25 pCi/L.
1992 EPA 1. EPA & CDC issue a revised "Citizen's

Guide" to radon.
2. Estimates radon causes 7,000 to 30,000
deaths annually, average of 14,000 deaths.
3. EPA's SAB reviews the revised EPA risk
estimate and concluded "a solid, well-
documented and defensible central estimate."
ATSDR Concludes that "even conservative estimates

suggest radon in one of the most important
causes of death." Reports that 14% of all
current cases of lung cancer could be
attributable to radon.
1993 ICRP A draft ICRP report finds the risks of radon

exposure to be essentially the same as
estimated by EPA and CDC in 1992. Action
level at 5 pCi/L.
1994 NCI Estimates 15,000 deaths from lung cancer

each year; approximately 10% of all lung
cancers.
NAS Recommends a re-analysis of the health

risks associated with radon based on the

accumulation of new evidence. The re-analysis

includes multi-disciplinary models for radon

carcinogenesis.

Modified from [HR 1994, p.12-14]








requires the Administrator to establish user fees on persons

manufacturing or importing devices, or offering services

covered by the performance and proficiency program.

There are four major tasks of HR 2448:

1) examine existing public awareness programs concerning

radon;

2) act as a coordinating body for the donation of resources

to assist in programs and strategies to raise outlets to

increase radon awareness;

3) encourage media outlets to increase radon awareness;

4) evaluate the accuracy and effectiveness and assist in the

update of such programs and strategies.

In the "Radon Awareness and Disclosure Act of 1994,"

the HR 2448 amends Title III of the Toxic Substances Control

Act (15 U.S.C. 2661 et Seq.) to improve the accuracy of

radon testing products and services, to develop a strategy

to identify and reduce exceptionally high indoor radon

levels, to promote and facilitate the testing and mitigation

of vulnerable premises, to promote radon resistant

construction in high radon areas, and to create a commission

to promote increased public awareness of the health threats

of radon exposure [HR 1994, p.11].








Radon and Liability

There have been several law involving radon problems.

In Wayne Vs. TVA 730 F.2d 392 (5th Cir. 1984), cert denied,

496 U.S., 1159 (1985) homeowners brought product liability

and negligence action against a phosphate slag producer

whose slag was used to make concrete bricks for the

construction of their homes. The verdict was in favor of

defendants, holding that homeowners' claims were barred by

the Tennessee Statute of Limitations applicable to product

liability actions; in Robles Vs. Environmental Protection

Agency 484 F.2d 843 (4th Cir. 1973) a homeowner sued the EPA

to get results of a radioactive survey and the names and

addresses of those owning homes exceeding EPA safety

guidelines. The circuit court judge held that information

gathered by EPA and relating to homes where uranium tailings

had been used for fill was not exempt from disclosure; in

Nobel Vs. Marvin E. Kanze, Inc., Civ. No. 02428, at 1

(Montgomery County Court of Common Pleas, Pa. 1983) the

homeowner sued a contractor after finding radon entering

through a crack in the ventilation system.

In the Nobel case, the homeowner sued for damages

including expenditures of money and time to detect the








source of the radon gas, the cost of mitigation for high

radon levels, repair and other expenses after mitigation [HR

1990, p.157] .

Most real estate professionals and mortgage bankers do

not require radon tests thereby leaving themselves and their

stockholders open to actions on negligence and liability

theory. Without a well-structured and phased plan to test

structures for radon, homebuilders, realtors, bankers,

construction companies and homesellers will face a

significantly worse position relative to liability and

negligence litigation in the long run. Congress and the

Administration should be aware of the basis for expected

tort action on radon. It is essential to have federal

regulation to save litigation costs.



Radon Decay Chain

Radon is formed directly from the radioactive decay of

Radium (Ra). The original source is Uranium (U). After a

series of decays, Rn (222Rn) is formed and becomes the most

serious decay product of Uranium. The decay flow chart of

Uranium is illustrated in Figure 2.2. Radon has three major

isotopes: 222Radon, 219Radon, and 210Radon which are the









Uranium and Its Decay Segences


5
10 yrs


222
Rn and Its Proaenv


days


26.8 min.


22.3 days


Stable


Figure 2.2. Decay Flow Chart of Uranium








most abundant in nature. The half-lives of the three

isotopes are illustrated in Table 2.3 Modified from [Lao

19901.

Most radon comes from soil or rocks and enters into

houses through cracks or penetrations. The traveling time

is the critical factor of radon progeny entry. Therefore,

the half-life of 219Rn, and 210Rn are both less than one

minute and they are less likely to enter the house before

they decay. However, 222Rn has chances of seeping into the

house. Therefore, radon refers to 222Rn in general. One

should be aware that the progeny of 222Rn (from 218po to

210pb) all have half-lives less than 30 minutes. If


inhaled, they are most likely to decay to 210pb before

removal by lung clearance mechanisms. The properties of

radon progeny are shown in Table 2.4 [Lao 1990, Qu 1993].



Radon Damage Mechanism

The short-lived radon progeny could be harmful if

inhaled because these elements could eject energy from a or P

particles. For example, the energy ejected from a 218po atom

disintegrating at the lung tissues deposits 7.7 Mev of

ionizing energy in the tissue. The damage to lung tissues













Table 2.3 Radon Isotopes and Their Half-lives
Isotope Half-life

222Radon 3.83 days

219Radon 55 seconds

210Radon 4 seconds


Modified from Lao [1990]


Table 2.4 Properties of Radon Progeny
Nuclide Radiation ray Half-life Potential a

Energy/atom(Mev)

222Rn ( 3.825 days 4.06

218po a 3.11 min. 13.7

214pb P- 26.8 min. 7.7

214i P- 19.9 min. 7.7

214po a 164 tsec. 7.7

Modified from Lao [1990], Qu [1993]









caused by the ionizing radiation of a particles is measured

in units of the a energy. Internal irradiation by a

particles is believed to be the cause of radon-induced lung

cancers. Because the penetration power of an a particle is

very poor, it loses virtually all its energy at one point in

the lung tissue. The a particles that are stopped by soft

tissues deposit a large number of ions within a few cell

diameters. This could kill a cell or cause mutation [Lao

1990, p.13].




Radon Measurement Units

The measurement units of radon concentration (222Rn)

and radon progeny are pCi/L and Working Level, respectively.


Radon Concentration

Radon concentration is measured in pCi/L or Bq/m3.

Curies (Ci) was named after Marie Curie (1867-1934) and

Pierre Curie (1859-1906). The conversion factors are listed

below

1 Bq = 1 disintegration/second

1 Curie (Ci) = 3.7 x 1010 Bq

1 pCi = 0.037 Bq









1 pCi/L = 37 Bq/m3


Radon Progeny

Working Level (WL) is the unit for measuring the

concentration of radon decay products. It is equivalent to

1.3 x 105 Mev of potential a energy from the short-lived

progeny per liter of air. In addition, one WL is in balance

with exactly 100 pCi/L of 222Rn. The definition of WL is

illustrated in Table 2.5 [Lao 1990, p.14] According to

Table 2.5, the total potential a energy per 100 pCi/L is
5
approximately 1.3 x 10 Mev.


Table 2.5 Definition of Working Level

Element No. of atoms Potential a Potential a

per 100 pCi/L energy per energy per 100

of 222Rn atom (Mev) pCi/L of radon

(Mev x 105)
977 13.7 0.134


8,585 7.7 0.661


6,311 7.7 0.486

214po
0 7.7 0


Total 1.281










Radioactive Decay

The time rate of change of a radioactive material is

defined as N (number/m3). The probability per unit time that

a nucleus will decay is defined as X which is independent

from any known physical or chemical process. The first order

differential equation is derived as [Lao 1990],

-dN/dt = XN dt

ln(N) = Xt + C (2-1)

Boundary conditions: at t=0, N=No, Plug in (2-1)

C = In(No)


N(t) = No e-Xt (2-2)

When t = T/2, N = 1/2 No,


where T/2 is the time period of a radioactive material to

decay to half its mass through the radioactive decay

process.

Plug in (2-2)

T/2 = ln2/X (2-3)

The half-life of a decay product can be calculated from

equation (2-3). For example, the decay constant for 222Rn is

0.00755 (h-1), the half-life of 222Rn is








T/2 = ln2/(0.00755)

= 91.81 hours

= 3.83 days


Decay Relationship between Parent and Daughter

The relationship of 222Rn with its decay product Po is

formulated as [Al-Ahmady 1994]

dNpo/dt = XRn NRn XPo Npo (2-4)

= Rn NORn e-IRnt X- po Npo


where NRn = NRn e-Rntl at t = 0.

Rearrange equation (2-4) as follows,

dNpo/dt + Xpo Npo = pRn NRn e-ljnt. (2-5)

Solving for the homogeneous solution for equation (2-5),

dNpo/dt + kPo Npo = 0
Npo = C e-kpot

Assume that the particular solution for equation (2-5) is


Npo = K e- Rnt plug in equation (2-5),

K (-XRn) e-Rnt + Ipo (K e-)Rnt) = kRn NRn e-"Int


K (kpo-_Rn) = kRn NORn


K = pRn NRn/(Xpo-IRn)








Therefore, Npo = C e-)Lpot + [XRn NORn/(Xpo-XRnl)]e-Rnt. (2-6)

Boundary conditions: when t=0, Npo=0. Solving equation (2-

6),

C = Rn NoRn/(Xpo-Rn).

Substitute C back into equation (2-6), then

Npo = [XRn NRn/(Xpo-pRn)] (e-kRnt -e-kpot) (2-7)

Apo = Xpo Npo, where Apo is the Activity rate (numbers/sec.


3 ). When t = tm, Apo reaches maximum. Where tm is the time

of maximum activity. To find tm, let dAPo/dt = 0.

[?Rn NRn/(Xpo-XRn)] [-XRn e-XRntm + -Xpo e-Xpotm)] = 0

tm = In(kpo/kRn))/(Xpo-kRn)) (2-8)

By re-arranging this equation,

Xpo Npo/(XRn NRn) = [Xpo/(?Po- Rn)] [1- e-(Xpo-kRn)t] (2-9)

When t -+ oo, po Npo/ (Rn NRn) = kpo/ (Xpo-kRn) (2-10)

Transit equilibrium activity concentration is balanced

when the ratio of daughter to parent activity is constant.

Special case, if

dLh/2 << P1/2 d = daughter, p = parent, then

d >> Xp.








Therefore, equation (2-10) becomes


kPo Npo/ (IRn NRn) = i1. (2-11)

This is the secular equilibrium special case of transient equilibrium

when the daughter and parent activities are equal.

For example, Tl/2 (Ra) = 1600 years, TI/2 (Rn) = 3.83 days,

XPo = 1.18 E-6 /day, XRn = 0.181 /day


XPo Npo/(XRn NRn) = 0.181 /(0.181-1.18 E-6) s 1.000007

and tm = ln(0.181 / 1.18 E-6)/(0.181 1.18 E-6) 66 days.



Summary

This chapter discussed radon risks, radon related legal

issues, and radon sources. Radon decay chain and its damage

mechanism were also presented.















CHAPTER 3
RADON TRANSPORT IN STRUCTURES


Introduction


This chapter focuses on substructure and superstructure

parameters to the radon entry. The important issues in

substructures are soil and soil radium content. Soil has

been found to be the key factor that affect radon intrusion.

Radium content in soil and its transport is introduced. The

major factors affecting indoor radon levels in

superstructures are concrete slab type, building materials,

house water and pressure-driven flow.


Review of Literature


Since the mid-1970's, the electric power industry has

been working on ways to give customers better choices for

controlling the quality of their indoor environment. This

work focused in part on evaluating the effects of building

design and systems operations on indoor radon levels [Harper

et al. 1988].

House radon concentrations depend on a variety of

factors (e.g., radon availability in the soil, interaction

of building and soil, weather forces affecting radon entry).

Research studies, sponsored by the Electric Power Research









Institute (EPRI) and the Tennessee Valley Authority (TVA),

and principally conducted by GEOMET Technologies, Inc., and

Oak Ridge National Laboratory, have examined the effects of

siting, building design and space condition operations on

indoor radon levels. These studies also examined the

effectiveness of different radon and progeny control

approaches. Soil is the principal source of indoor radon in

single-family houses in the United States [Nero and Nazaroff

1984]. Pressure-driven flow is a principal means by which

soil gas enters houses; it is expected to be the predominant

source of radon in houses with elevated concentration. There

are three principal causes of basement depressurization

[Garbesi and Sextro 1989]: thermal differences between

indoors and outdoors, wind loading on the building

superstructure, and imbalanced building ventilation.

Soil-gas entry due to basement depressurization has

been experimentally demonstrated by Nazaroff et al. (1987).

Entry pathways have been assumed to be penetrations, gaps,

or cracks in the building substructure. A demonstration of

a previously neglected pathway for soil-gas entry into

houses is pressure-driven flow through permeable, and below-

grade building materials. Such a flow, distributed over the

wall area, could occur via porous building materials or via

a network of small cracks. If this pathway is ignored in the

modeling of soil-gas entry into buildings, predictions of

the soil-gas entry rate could be substantially too low

[Garbesi and Sextro 1989].









Research Subjects


This research focused on the relationship of the

construction to the radon intrusion. The analysis was based

on the research projects of New House Evaluation Program of

Florida. The research analyzed all aspects of building

behavior from substructure to superstructure. The subjects

investigated are illustrated in Figure 3.1. Major subjects

researched include:

1) Soil

2) Concrete slab

3) Penetrations (plumbing, joints)

4) Building materials

5) Pressure differentials (HVAC systems, ventilation,

wind, temperature)





Ventilation

Wind

SBuilding Materials


HVAC


Crack
Ca Penetrations

Concrete slab


0 0O
o


o 0 o


Figure 3.1 Major Research Subjects









Sources that Contribute to Indoor Radon


The sources that contribute to indoor radon

concentration are:

1) Soil

2) Building Materials

3) House water

4) Ambient air


Radon Transport in Substructures


Radon in soil will be discussed in detail and the

related movement parameters will also be discussed. Soil

radium content, radon emanation coefficients, and soil

permeability will be introduced.


Radon in Soil and Its Movement


For most houses with high indoor radon concentrations,

soil is the principal source of radon [Nero and Nazaroff

1984; Nazaroff et al. 1988; Revzan and Fisk 1992] Soil

radon gas is estimated to contribute 85% 90% of indoor

radon among the sources [Clarkin and Brennan 1991]. Since a

large percentage of radon source comes from soil, the main

focus of the radon source is on the soil of the building

site. Figure 3.2 illustrates the radon sources and the

factors that affect their entry. Considering the sources

that affect the concentrations of soil radon, the

radioactive decay of radium is the primary contributor.














Process


Flow mechanism





in




a. Permeability ;


b. Diffusion length


Affecting factors

1. Temperature different
2. Windspeed
3. Barometric pressure changes
4. Precipitation
5. Changes in water table
6. Snow or ice cover
7. Building appliance (HVAC,fireplace)


* Soil grain-size distribution
.Moisture
. Porosity
S1. Moisture
2. Porosity


Figure 3.2
Parameters


1 I. Moisture
eating factor 2. Soil gas distribution
3. Temperature
4. Intragranular location of Ra atom








Soil Gas Radon Entry Mechanism and Affecting









Elevated soil radium concentrations may cause higher
rates of radon generation in the soil air; therefore, the
soil radium concentration should be considered in the
foundation soil.


Radon Emanation Coefficients


The fraction of radon generated from soil grains that

enters the pore volume of the soil is the emanation

coefficient. Emanation coefficients for soil range from 0.05

to 0.7 [Rogers et al. 1989; Nazaroff 1992]. The emanation

coefficients for 48 Florida soil samples averaged 0.33

[Rogers and Nielson 1991a, p.3-3]. Moisture content has

been demonstrated to have a large effect on the emanation

coefficient of radon from uranium ore tailings, concrete,

and soil [Nazaroff 1992, p.143]. The emanation coefficient

is much lower if the source material is dry rather than

moist. Moisture content dependence to emanation coefficient

is presented in Figure 3.3 [Nazaroff 1992, Fig.5]. The

figure suggests that high moisture content soil has higher

emanation coefficient than low moisture content soil. The

reason for this could be a lower recoil range for radon in

water than in air. Temperature changes have been found to be

a factor in determining the radon emanation coefficient.

When soil temperature was increased from 50C to 500C, the

emanation coefficient increased by 55% [Nazaroff 1992].













Moisture content (vol. %)
5 10 15


0 2 4 6 8
Moisture content (wt %)

Figure 3.3 Effect of Moisture Content on the Relative
Radon Emanation Coefficient [Nazaroff 1992]




However, the soil temperature does not change much. This

effect could be neglected.


Indoor Radon Prediction Model


Pressure driven from the house due to appliances,

thermal gradients, heating and air conditioning systems or

winds, pull the soil air with its radon gas into the house.

The movement of the air depends on the soil

permeability. The higher the soil permeability, the easier









the gas moves. An indoor radon prediction model was made by

Mose [Mose et al. 1992] using soil radon and soil

permeability1. The prediction model was successful for most

of the houses in northern Virginia and southern Maryland.

The prediction model is shown in Figure 3.4. Mose et al.

(1992) proclaimed that their estimates are very useful for

indoor radon prediction. However, the indoor radon

concentration is affected by more factors than their model

took into account. Therefore, more parameters should be

taken into account in order to have a better prediction. The

parameters, such as soil permeability, soil radium content

and foundation type are crucial to the indoor radon

elevation.


Soil Permeability


Soil permeability is associated with soil porosity,

moisture, and grain-size distribution. A theoretic equation

for soil permeability for laminar flow in saturated course

grained soils is described as [Scott 1969]:

K = [I1/(5.0 Ss2)] [n3/(n-1)2] [yw/']

Where

k = K (11/Yw)

K = Hydraulic conductivity (m/hour)

k = Soil permeability (m2)




1 The permeability of this case is defined as inch/hour which is the
velocity of the fluid flows through the soil.













400

330
Soil radon
(pCi/L) 200
100(

0


I


0 0.5 0.5 1.0 1.0 5.0 >5.0
Soil permeability (in/hr)

Poential indoor radon risk(pCi/L

Low (0 5)


I I


I I


Medium (5 -15)

High (15 and above)


Figure 3.4 Indoor Radon Prediction by Using Soil Radon2
[Mose et al. 1992]















2 The permeability (in/hr) of this case is sometimes defined as
hydraulic conductivity.









Ss = Surface are of the particles in unit volume

of the solid material

n = porosity

Yw = unit weight of water

= viscosity of water.

For sandy soils, Hazen suggested that the approximate

value of K is given by [Scott 1969]:

K = C (DI0)2

where

C = a coefficient varying between 0.01 and 0.015

D10 = effective size of soil in mm

An empirical model for predicting soil gas permeability

is defined as [Rogers and Nielson 1991b]:

k = (p/110)2 d4/3 exp(-12 m4)

where

k = soil gas permeability (cm2)

p = total soil porosity dimensionlesss)

d = arithmetic mean grain diameter (cm),

excluding >#4 mesh material

m = moisture saturation fraction dimensionlesss).

The radon diffusion coefficient factor is derived by

Rogers [Rogers and Nielson 1991b] as:

D = 0.11 exp(-6mp-6mp14p)

where

D = radon diffusion coefficient (cm2/sec).

Subslab soils are ranged from coarse sand to fine clay.

The smaller particle silts and clays have higher ambient









moisture contents and generally lower permeability and

diffusion coefficients; therefore, radon gas in the soil air

cannot move as easily to the entry points onto the house.

Both K and D decrease significantly with moisture for m>0.5.

Soil moisture content is controlled in large part by

precipitation. Fine grained soils such as silts and clays,

have higher moistures under normal environmental conditions.

Therefore, they have lower K and D values than sands. Radon

gas does not move as easily through them. However, for a

specified radon entry rate into a house, the silts and clays

can have higher radium content because more of the radon gas

is held in the soil.

The permeability and diffusion coefficients are closely

related, and exhibit similar trends with soil type, degree

of compacting and moisture. Thus the permeability

coefficients can be used to specify soil conditions in a way

that also includes the effect of diffusion. The average soil

permeability of soils is listed in Table 3.1 [Yegingil 1991,

p.181].

Clay and silt have very low permeabilities and the

radon entry rates are very low compared to the sandy soils.

Revzan and Fisk (1992, p.42) observed that when the soil

permeability is less than 10-12 m2, the soil-gas velocity at

the openings in the basement shell is low and diffusion is

the principal means of radon entry. In this case, the radon

entry will be dependent on the concentration of the soil gas

radon.


















Table 3.1 Soil Permeability

Soil type Soil Relative Degree of

permeability Permeability

(cm/sec)

Gravel 10-3 10 6 High

Clean sand 10-5 108 High

Silty sand 10'6 10-10 Medium

Silty 10 10-12 Low

Glacial tilt 10.9 10-15 Low

Marine clay- 10 15 Very low to

practical

impervious

Modified from Yegingil [1991]









Radon Flows through Different Soil Layers


In construction practices, a layer of fill earthen

materials is placed between the concrete slab and the top of

the natural soils. The natural soils may consist of several

layered soils. The layered soils have their own properties.

However, the top layer has the most significant impact to

the radon entry. However, if the second layer of soil

contains high radium and the top soil has high permeability,

elevated radon concentrations may occur.

Rogers and Nielson (1991b) measured indoor radon levels

often exceeding 10 pCi/L, even though the radium

concentrations in the sandy soils immediately beneath the

slab are less than 1 pCi/g. Measurements of subslab radon

are several thousand pCi/L, indicating that the radon is

mainly coming from soils in the Hawthorn Formation. Soils

in the Hawthorn Formation have radium concentrations ranging

from 5 to 30 pCi/g in this area. Soil gas radon is a

reliable indicator of a potential radon problem which was

suggested by many researchers [EPA 1991].

Different layers have different soil permeabilities and

which is one of the important factors that affects radon

entry. Soil permeability of different layers may be

calculated as follows [Todd 1980]:

Qx = K1 I Z1 + K2 I Z2 + K2 I Z2

= I (K1 Z1 + K2 Z2 + K2 Z2)

Also, Qx = Kx I (Zi + Z2 + Z2)









where

Qx = Flow rate in the x direction (m2/s)

Ki = Hydraulic conductivity (m/s)

I = Hydraulic gradient

Zi = Depth of Layer i (m)

Kx = Overall hydraulic conductivity in the x direction

k = Permeability (m2)
Surface

Z2
ql ---


Qx l q2 No. Z2


q3 -- Z3





Qz
t= Dynamic viscosity

p = Fluid density

g = Acceleration of gravity (m/s2)

Therefore,

Kx = (KI Z1 + K2 Z2 + K2 Z2)/(Z + + + Z2) (3.1)

k = K (3.2)
pg

Assumption: Assume that equation (3.2) holds for gas.

Substitute (3.2) into (3.1),

kx = (ki Z1 + k2 Z2 + k2 Z2)/(Zl + Z2 + Z2) (3.3)

In general form, kx = Xki Zi/(EZi)









Similarly, kz = 7 Zi /(E(Zi/ki)) (3.4)

The ratio of kx/kz usually falls in the range of 2 to 10 for

alluvium, but values up to 100 or more occur where clay

layers are present [Todd 1980, p.81].


A Proposed Mitigation Method


Because the kx/kz ratios of soils are large, the

horizontal movement of the soil gas radon is faster than

vertical movement. According to this phenomenon, a radon

reduction method is proposed. The proposed method is

illustrated in Figure 3.5. There are two or more vertical

two-inch PVC pipes needed connecting the perforated pipes.

There is a slope of the perforated pipe for ease of gas

movement. The pressure driven flow may dominate the

diffusion movement of the radon gas; however, the perforated

pipes could reduce the pressure differentials between

subslab and indoor (so called pressure break). The

perforated pipes can produce equivalent pressure between

subslab and atmosphere.

In addition, the PVC pipes connect the shower water to

the soil. The pipes discharge water into the soil and keep

soil moisture content high, which could slow radon movement.


Soil Permeability in Different Depths


Soil permeability is affected by soil pressure. Figure

3.6 illustrates the soil permeability distribution under









different consolidation pressures [Hoddinott and Lamb 1990].

High pressure tends to reduce soil permeability.

Because of soil pressure, the deeper the soil the

higher the pressure is. However, the soil pressure in the 10

feet range which we consider affecting indoor radon

elevation, does not change drastically. However, the

pressure differentials from indoor to outdoor has been

proven to dominate the transport of the soil gas radon [Lao

1990].












p__ Cap



3 inch PVC Pipe




Perforated Pipe

3 inch PVC Pipe

Figure 3.5 Soil Gas Radon Mitigation by Perforated Pipe
Systems





42




1.00E-08 -- .... ...... ........ ........
r. 9.00E-09 ------ -------- ...................
E 8.00E-09 .
r 8.0 0E-09 -- -- --- .. ........ ........ ....... -
TOO7.0E-09 -------\ .-----.------------------.---.
7 6.00E -09 ..... ... .. .. -- -. ...- .. ...- ... .. ..
6 5 .0 0 E -0 9 - .. ... . ..
-^ 4.00E-09 -------- --*-^ ,- ---.-----
7.00E-09 .------- .


E 2.00E-09 --------------- --------------W------
a) 1.00E-09 ----------.-----------------
O.OOE+00
4.00E-0 ------------i--------.........


12.5 25 50 100 200
Consolidation Pressure (Kpa)

Figure 3.6 Permeability Distribution of Different Pressures



Radon from Geological Consideration


Many researchers have confirmed that the relationship

between geology and indoor radon is complicated and

dependent on climate, terrain, bedrock composition and soil

permeability. Geology controls the chemical composition of

the rocks and soils from which radon is derived. Climate

exerts a strong control over the temperature and moisture

content of soils, thus affecting radon emanation and

physical and chemical weathering of the soils and rocks.

Indoor radon assessments often rely on factors such as

bedrock geology or soil permeability to predict the

potential of an area for radon. Rock types that are most

likely to cause indoor radon problems include carbonaceous

black shales, glauconite-bearing sandstones, certain kinds

of fluvial sandstones and fluvial sediments, phosophorites,









chalk, karst-producing carbonate rocks, and so on. Rocks

least likely to cause radon problems are marine quartz, and

certain kinds of non-carbonaceous shales and siltstones,

certain kinds of clays, silica-poor metamorphic and igneous

rocks, and basalts. Mafic rocks are characteristically a

poor radon source. Rocks such as aluminous and feldspathic

gneiss, schist, and phyllite vary but are generally sources

of moderate to high radon. Granites and sheared rocks are

generally sources of very high radon [Gundersen 1993,

p.IV1]. Figure 3.7 shows the average soil radon

concentration distribution vs. indoor radon concentrations

[Gundersen 1993, p.IV4].

The glacial lake deposits are composed of fine sand,

silt and clay. A very high correlation between indoor radon

and soil radon was found in Gundersen's research when the

measurements were grouped by glacial deposit and the

measurements were averaged. However, if the measurements

were grouped by bedrock type the regression only yielded an

R=0.21. Therefore, glacial deposits are better predictors

of indoor radon and radon sources in soil than bedrock

geology. Figure 3.8 illustrates the average indoor radon

levels vs. soil radon concentrations [Gundersen 1993,

p.IV5].


Geological Elevated Radon Summary


The rocks which the have highest uranium contents are









.I
1000
Ua.
p.


100





10




I-


sheared gneiss @


sheared gneiss- sheared granite


sheared mafic and schist
gn phyllite
gneiss 111yi

/ schist
1 gneiss
mafic rocks
y = 62.35 9.16e-2x R 0.81
5 .


0 1000 2000 3000 4000 5000

Average Soil Radon. pCt/L


6000


Figure 3.7 Average Indoor Radon Levels vs. Soil Radon
Concentrations [Gundersen 1993]


2000


1500



1000



500


0 2 4 6 8 10 12 14 16 18 20


Average Indoor Radon pCi/L



Figure 3.8 Average Indoor Radon Concentration vs. Soil Radon
Concentration [Gundersen 1993]


I


II









certain types of granite, black (carbonaceous) shales, and

phosphoric rocks. The common range of uranium concentrations

is between 2 to 10 ppm with averages around 3 to 4 [Lao

1990].

Geological areas having granites with more than 10 ppm

uranium could have a high radon potential. Uraniferous black

shales usually have an average uranium concentration of up

to 20 ppm. Phosphate rocks with 100 ppm uranium are very

common. High-grade phosphates may be a significant source

for elevated radon levels [Lao 1990, p.28].


A Generalized Geological Map for the State of Florida


A research performed by Otton (1993) shows that the

geology of Florida is dominated by fluvial, deltaic, and

marine sedimentary rocks. The older sedimentary rocks,

mostly limestone and dolomite, are exposed in a structural

high centered in Levy County along the western side of

peninsular Florida. Younger sedimentary rocks occur

throughout southern Florida, along the Atlantic coast, and

coastal areas of the western panhandle. A generalized

geology map is shown in Figure 3.9 [Otton 1993, IV-5].

Uraniferous phosphatic sediments occur in the Alachua

Formation, the Hawthorn Group and Bone Valley Formation

[Sweeney and Windham 1979]. Although only a few occurrences

of uranium minerals have been described in Florida, where

these unraniferous phosphatic rocks are mapped, high












































0 50mi


Figure 3.9 Generalized Geology Map of Florida [Otton 1993]









Legend of Figure 3.9
Type Stratigraphic Unit General Major
lithology litholo-
gic unit
Surfical and terrace Quartz sands with
Qs sands. Undifferentiated. varying proportions Sand
of silt, clay,
organic material and
carbonate.
Lake Furt Marl, Miami Fossiliferous
Qtl Limestones, Key Largo limestone, maris and Limestone
Limestone, Anastasia lesser amounts of
Fort Thompson, sand and clay.
Caloosahatchee, Tamiami
Formation.
Undifferentiated.
Citronelle and Miccosukee Clays and quartz Sand and
Ts Formation. sands with lesser clay
Undifferentiated. amounts of silts and
gravels.
Chariton, Jackson Bluff, Shell maris, clays Marl and
Tm Red Bay, Yellow River, and quartz sands sand
and Chipola Formation. with minor
Undifferentiated. limestones.
Bone Valley, Alachua, Sands, silts and Phospho-
Tp Fort Preston and Hawthom clays with lesser ritic
Formation (Group). amounts of clay and
Undifferentiated. limestone, dolomite sand
and phosphorite.
St. Marks, and Impure limestones
Tl Chattahoochee Formation. with sand and lesser Limestone
Undifferentiated. amounts of
limestone, dolomite
and phosphorite.
Suwannee Limestone, Ducan Limestones which may
Tol Church Beds, Byram be slightly sandy or Limestone
Formation and Avon Park dolomitic.
Limestone.
Undifferentiated.
Crystal River, Willston, Fossiliferous Limestone
Tel and Inglis Formation Avon limestones and and
Park Limestones. dolomite dolomite
Undifferentiated.









concentrations of uranium (up to a few hundred ppm) in near-

surface soils and bedrock are known to occur. South Ocala is

described to have this type of rocks [Espenshade 1985].

Soils containing a few tens to a few hundreds of ppm of

uranium are likely to be strong sources of radon. Surface

materials in southernmost Florida are composed mostly of

peat, sand, and limestone. Sand, silt, shell, and clay are

the primary surface materials along the Atlantic Coastal

areas from Lee County to Pinellas County. Refer to Figure

3.10. Surface materials across most of the state are low in

uranium content with most of the state showing less than 1.5

ppm equivalent uranium (eU).

A strip of land about 60 miles wide along the Atlantic

Coastal margin extending from Jacksonville southward to

Miami is almost entirely below 1.5 ppm. However, the

highland areas in the north and north central part of the

State generally range from 1.0 to 2.0 ppm eU.

Higher readings occur in an area underlain by

phosphatic rocks that extends discontinuously from southern

Polk County northward to southern Columbia County, including

an area of a few hundred square miles averaging greater than

5.5 ppm eU. Dade County underlain by thin sandy soils
















EXPLANATION


SGravel and coarse sand

Sandy clay and dcay

Medium to fine sand and silt

!Il S
|^ U Limeson and dokmifa \tfST ti Y

sd Sand. shall and dclay



0 50mi | ,






Figure 3.10. Generalized Surface Materials Map for the
State of Florida [Otton 1993]









covering shallow limestone bedrock, has equivalent uranium

values as high as 3.5 ppm.



Phosphate Region and Indoor Radon Levels in Florida


A study of the phosphate region of Florida which was

investigated by Roessler et al. (1983) is shown in Figure

3.11. The indoor radon level of houses in Florida is shown

in Figure 3.12 [DCA 1994] Figure 3.12 shows the tested

results of average indoor radon levels of the Florida

houses. There is a similarity between these two figures;

areas interpreted as highly phosphated have high indoor

radon levels.


Summary of Radon Transport in Substructures


Radon sources are mainly from soils and rocks. The

radon levels are affected by permeability, soil moisture

content, radium content, and pressure differentials. Highly

phosphated area have high indoor radon levels as

demonstrated in Figures 3.11 and 3.12.


Radon Transport in Superstructures


The following sections will discuss the factors in

superstructures that are significant to the elevation of

indoor radon. These factors include concrete slab, building

materials, house water, and pressure differentials. These











































Figure 3.11 Phosphate Distribution in Florida [Roessler et
al. 1983]













d
.rq



H

-4-






O
U


0)












a,)
0





















CO
-Iq
















r-
1-4
.0

























-H
be
1:3









factors have been researched seriously in the FRRP research

projects. The results and their interpretation will be

discussed.


Radon Transport through Concrete Floor Slab


Radon gas can seep into houses because of the pressure-

driven flow through concrete slab cracks, plumbing

penetrations and wall-slab connections. Diffusion of radon

from subslab soil through concrete floor slab and radium

decay of concrete itself may contribute to the concentration

of indoor radon. The ACRES (1978, p.5) report suggested

radon diffusion from or through concrete cannot be a

significant source of radon entry.

Tanner (1990) identified radon diffusion as a

significant mechanism when foundation soil permeabilities

are less than 7 x 10-12 m2. Subsequently, Rogers and

Nielson (1990) investigated diffusion through concrete

floors and the contiguous soil as a significant mechanism

for radon entry for many soils under typical long-term

average foundation pressure gradients. This paper

characterizes the radon generating properties of Florida

concretes. The parameters measured are the radium

concentrations and emanation coefficients of Florida

concretes and their constituents. The radon generation and

transport through Florida residential concretes are examined

for their contribution to indoor radon concentrations. The









paper also identifies the main properties of concrete

performance that influence radon migration from the subsoil

into dwellings. In addition, Loureiro et al. (1990) have

compared theoretical diffusion and convection radon

transport in soils to estimate conditions when diffusion is

insignificant.

The diffusion coefficients as measured from the Florida

concrete slabs by Rogers and Nielson (1992) range from 1.8 x

10-4 cm2 s-1 to about 4.6 x 10-3 cm2 s-1. In general, the

diffusion coefficient increases with water/cement ratio. The

permeability of the concrete slab is very low and averages

5.34 x 10-12 cm2. This value falls in the permeability

range of silt clay. Thus, the transport mechanism is mainly

from diffusion. The radium and emanation are the source

index of radon diffusion. The radium ranges from 1.0 pCi/g

to about 2.4 pCi/g. The emanation coefficients averaged 0.07

which is very small.

The measurements in Florida by Rogers and Nielson

(1992) showed radium concentrations averaged 1.52 pCi/g, and

the average emanation coefficients of aggregates are less

than 0.08, which is a very low emanation value; therefore,

their radium contents are less important than the radium in

cement components. Concrete with a radium content less than

2 pCi/g contributes less than 10 percent to the total radon

entry in the example dwelling. The radon transport through

the concrete slab by diffusion and radon diffusion from the









concrete slab itself have proven to be minor contributions

to the indoor radon.


House Water


Radon gas can be dissolved in cold water. As was

experienced by the University of Florida research team when

it rained one day before site screening, the reading was

lower than usual and in some cases had extremely low

readings. Radon can be dissolved in water and released in

the air when showering, dishwashing, and washing clothes.

It is estimated that 10,000 pCi/L of radon in water will

contribute about 1 pCi/L of radon to the indoor air [Lao

1990, p.18].

Research also shows that using only well water

presents a problem. For the houses using water from public

utility systems, waterborne radon in general does not

contribute significantly to the indoor radon concentration.

Because the public water is supplied from treatment plants

and stored in storage tanks, after it reaches the houses,

most radon may have decayed already (half-life 3.8 days).

For those houses which have a problem with water radon,

two cost-effective treatment methods that can be utilized to

remove radon from water supplies [Lowry and Lowry 1988] are:

1) Granular Activated Carbon (GAC) Adsorption/Decay

2) Aeration.

In the first method (GAC), research shows that this









method is successful in reducing radon from over one million

pCi/L to less than 500 pCi/L, for a 99.9% removal

efficiency. The key to the effectiveness of GAC method is

the adsorption/decay steady state that occurs for radon and

its short-lived daughters.

The aeration has three major methods: diffused bubble,

spray, and counter current packed tower. It has been

verified that the diffusion bubble method reduced 250,000

pCi/L of radon to 50 pCi/L [Lowry and Lowry 1988]. The usage

of the GAC or aeration will be determined by the capital and

operation/maintenance (O&M) costs. It is summarized in Table

3.2.

For household supplies, the GAC method is the most

economical alternative. However, with flows greater than

20,000 gpd, packed tower aeration is the most cost-effective

method [Lowry and Lowry 1988]. Housewater may contribute a

significant amount of indoor radon if the water radon level

is high. Most high water radon levels are from wells;

however, nowadays, the use of well water is insignificant in

comparison to the use of municipal water supply.


Emanation from Building Materials


While radon emanation has been studied for more than

two decades, the earlier studies suggested that construction

materials were the most important source of indoor radon

elevation. More recent studies have proved that radon










Table 3.2 Utilization and Costs of Water Radon Mitigation
Methods

Supplies Method Installation 0 & M

Flow (Gpd) cost ($)

Household GAC 800 Negligible

50-500

Multi-unit & Spray 2300 High

small community

500-20,000

Municipal Pack tower Vary High

>20,000 aeration

Modified from Lowry and Lowry [19881



transport from the soil or rock adjacent to the building is

the major factor. An emanation test was performed by

Fleischer et al. (1984) and suggests that the local

materials contribute much less radon per unit mass than do

the geological materials that surround homes or that are

used indoors for heat storage. Table 3.3 illustrates the

average values of the radon emanation rates. Radon

emanation depends strongly on temperature and relative

humidity [Wu and Medora 1987].

It was found that radon emanation could be reduced when

coatings were applied on the testing materials. The results

showed that when Semi-glass ALKYD Enamel A40-w5 and Epoxy

Paint were applied on the testing block, the emanation rates









Table 3.3 Radon Emanation Rates

Material Emanation rates

(atoms/gm-sec)

Soil 0.0065

Sand 0.0024

Brick 0.0012

Wallboard 0.00014

Stone 0.0012

Modified from Fleischer et al. [1984]



were reduced by 97.5% and 85%, respectively. However, this

test was performed in a closed room which may not be

realistic to the actual emanation rates.

Emanation rates for concrete, brick, and natural gypsum

are 0.0009-0.0003, 0.00001-0.005 and 0.002-0.02,

respectively [Morawska and Philips 1991]. It shows that

gypsum has very high emanation rate in comparing to concrete

and brick. In new construction, materials with high radium

content, such as gypsum and phosphate should be avoided.


House Ventilation


Ventilation is defined as the total rate at which

outdoor air enters a house. Ventilation has three components

[Nazaroff et al. 1988; Ward et al. 1993]:

1) Infiltration: uncontrolled leakage of air into a

house which occurs through cracks, and penetrations in the









house envelope;

2) Natural ventilation: the flow of air into the house

through open windows and doors;

3) Mechanical ventilation: forced supply or removal of

air by means of blowers or fans.


Ventilation Rates and Indoor Radon Concentrations


It is assumed that increasing ventilation decreases

indoor radon concentration because the higher air change per

hour (ACH) rate dilutes the indoor radon concentration. This

phenomenon was proved in the UF research that in nearly all

cases the general trend was that indoor radon and house

ventilation rates are in opposite directions. Figure 3.13

illustrates the opposition between indoor radon

concentration and house ventilation rate.


Radon Entry Rate


Radon entry rate can be measured by measuring both

radon concentrations and ventilation rates over the same

time periods. The governing equation of the radon entry

rate can be described as [Hintenlang et al. 1994a]:

dC/dt = [R-QC]/V X C (3.5)

where c = indoor radon concentration (Bq/m3)

= radioactive decay constant of 222Rn

Q = volumetric air flow rate through the structure

(m3/s)





60





(JaiPl/!id) NOllVUIN30NOO NOGVU
It) I) u) It) it if
n i In I It ci c i C i- CO





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o NO- -- 0 3-
(jnoLj/se6uBip Jig) 3J.VU NO1.V-11iN3A









R = radon entry rate (Bq/s)

V = house volume (m3)

Q is related to the house ventilation rate by:

Q = Xv V with Xv the house ventilation rate.

Equation 3.5 has the steady state solution:

C = R/[Q+ Xv V]
However, the truly steady state conditions are not achieved

in houses because the ventilation rates are continuously

varying. The solution of equation 3.5 can be solved

numerically for a time interval, At. The discrete form for

this solution is then:

AC(t+ At) = {V-1 [R(t) C(t) Xv (t) V] Xd C(t)} At,

rearranging this equation,

R(t) = [(C(t+At) C(t)/At) + Xd C(t) + Xv C(t)]V (3.6)

By using this solution technique, radon entry rates

were calculated as a function of time for each of the

research houses. Radon entry rate with respect to time is

shown in Figures 3.14. and 3.15. According to Figures 3.14

and 3.15, the calculated radon entry rates are relatively

constant throughout the measurement period. Most houses

exhibit variations between maximum and minimum entry rate no

larger than a factor of two. The periodicity of the radon

entry rate variations are similar to the periodicity of the

































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z,



"--
09


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(s/bg) 3I.v ALLN3 NOGVU


















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radon concentrations and ventilation rate. Besides the

periodic variation, the entry rates for most houses remained

relatively constant throughout the test. No significant

variations of radon entry rate corresponding to changes of

the HVAC operation configuration were observed period

[Hintenlang et al. 1994a, p.114]. These results provide

direct evidence that the operating configurations of the

HVAC systems do not affect the radon entry rate in these

structures. The average radon entry rates across the

measurement periods for each of these houses are shown in

Table 3.4. Table 3.4 demonstrates that all of the houses

have similarly small entry rates even in the presence of

indoor depressurization or pressurization. This result

indicates that the passive radon barriers installed in these

houses were effective in limiting radon entry into the

structure's interior.


Pressure-driven Flow


One of the EPA's recent research projects was the

feasibility study of basement pressurization using a forced-

air furnace. The EPA's 2-year systematic study of three

Princeton University research houses clearly demonstrates

that radon entry rates depend directly on basement

depressurization. The results also clarify the role of

natural ventilation in reducing indoor radon concentrations.

Natural ventilation is a simple way to reduce indoor radon









Table 3.4 House Radon Entry Data

House Indoor Air Change Radon Radon Entry

Number radon Rate (h-1) Entry Rate Flux

(pCi/L) (Bq/s) (Bq m-2 s-1)

1 2.3 0.49 8.6 0.046

2 3.0 0.33 9.5 0.044

3 2.2 0.34 4.1 0.017

4 2.7 0.27 4.9 0.034

5 2.5 0.31 5.2 0.024

6 4.2 0.26 5.9 0.032

7 2.7 0.38 6.9 0.032

8 2.8 0.21 2.8 0.025

Average 2.80 0.32 5.99 0.032


Modified from


Hintenlang et al.


[1994a, p.115]


levels; however, until now, there has been no information on

how much reduction to expect. The natural ventilation

decreases radon levels in two ways:

1) by simple dilution;

2) by providing a pressure difference.

The pressure break reduces both depressurization and

radon entry. In the Pennsylvania project, Radon Mitigation

Branch (RMB) demonstrated that a typical forced-air furnace

system could be installed to pressurize a basement to reduce

radon entry. The system reduced radon levels from 19.3 to

1.5 pCi/L in summer conditions [EPA 1992].









Another technique was the application of small fans for

active soil depressurization (ASD) in new houses. The EPA's

proposed model standards for controlling radon in new

buildings include placing a layer of aggregate and barrier

under the slab. By meeting these standards and sealing the

slab, it may be possible to use smaller fans than those now

used for ASD systems in existing houses. Smaller fans cost

less to install and operate, require less space, and may be

quieter.

A third project was a simple model for describing radon

mitigation and entry into houses. This model uses simplified

assumptions about the distribution of radon entry routes and

driving forces to relate indoor radon levels to soil

characteristics. Under these assumptions, the model shows

that:

1) soil permeability is the most important influence on

indoor radon concentrations because soil permeability varies

naturally by five to six orders of magnitude;

2) the area of the radon entry route is not very

important;

3) 90 percent of the total soil gas flow occurs in a

band surrounding the house with a width six times the depth

of the basement;

4) because radon decays, only the volume of soil within

a band, if the width is about two times the basement depth,

actually contributes to indoor levels.









The most updated UF research is the Sub-Slab

Depressurization (SSD) systems. This project was finished in

December, 1994. The new house evaluation program was to

develop standards to be adopted in future building codes and

to develop and test new protocols for measurements for

future research. The measurements include soil tests, soil

permeability, soil characterization, pressure field

extension, crack characterization, air infiltration and

leakage, tracer gas testing, short term radon tests and

long-term radon tests.

Pressure differences generated from the interactions

between the indoor, outdoor and sub-structure area under

different environmental and occupation conditions are

responsible for elevated indoor radon concentrations.

Hintenlang and Al-Ahmady (1992) have verified

experimental evidence that semi-diurnal pressure

differential driven radon entry exists for a slab-on-grade

structure built over low permeability soil. Mathematical

treatments predicting the sub-slab air volume pressures and

the pressure differentials across the slab have been

correlated to the atmospheric tidal barometric pressure

variations and are found to be responsible for significant

increases in indoor radon concentrations [Al-Ahmady 1992,

Hintenlang and Al-Ahmady 1992].

Al-Ahmady and Hintenlang (1994a) have also demonstrated

that temperature induced pressure differences can be a

significant influence on radon driving forces and









consequently the indoor radon concentrations under

particular configurations associated with the utilization of

the HVAC system [Al-Ahmady and Hintenlang 1994b]. The

effects of air infiltration rates, that are governed by the

differential pressure across the structure shell, on indoor

radon concentrations can be attributed to the exchange and

dilution of indoor radon with ambient air having much lower

radon concentrations.

Pressure-driven flow has proven to be the major driving

force of radon entry. However, UF research has found no

evidence that suggests the radon entry rate correlates with

across slab differential pressure [Hintenlang et al. 1994a,

p.124]. Figures 3.16 and 3.17 illustrate the differential

pressure data across the slab for houses at Summit Oaks and

Robin Lane. Pressure differentials would be expected to be

the major driving forces for the conventive entry of soil

radon gas, but no correlation is observed. Therefore, we may

infer that the presence of the radon-resistant barriers

implemented in these houses does greatly reduce the

pressure-driven flow of radon.


Summary of Radon Transport in Superstructures


Radon Transport by concrete diffusion is not

significant compared to pressure-driven flow. Most house

water, building materials have minor effect to the elevation

of indoor radon level.

















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CHAPTER 4
ANALYSIS OF HOUSE RADON AND CRACK STUDY


Introduction


This chapter analyzes the correlation between various

factors that might have an effect on the entry of radon. The

data are mostly extracted from reports and laboratory

experiments of the research projects in the New House

Evaluation Program of 1992-1993. The effectiveness of the

mitigation methods employed in UF projects is discussed.



House Characteristics and Soil Radon


House physical characteristics which include foundation

type, total crack length, and soil permeability (project

1992) are presented in Table 4.1. The grab counts1 of the

soil radon readings for each house are also listed in Table

4.2 [Najafi et al. 1993]. Soil radon grab counts were taken

four hours after a site screening. The soil permeabilities

are mostly in the range of 1.0 x 10-11 to 1.0 x 10-12 (m2)

which is at the low permeability range (Refer to Chapter 2,

this permeability is in the range of clay soil). Data for

the project of 1993 are illustrated in Tables 4.3 and 4.4.



1 "Grab count" means soil radon taken four hours after sampling.

71














Table 4.1 House Characteristics (Project of


Hous Foundation Total Soil permeability Soil

# type crack (m2) radon

length (Grab)

(ft) pCi/L

1 Monolithic 13.5 3.92E-12-1.69E-10 690

2 Stemwall 1 1.47E-11-1.13E-11 5300

3 Stemwall 0 8.18E-13-3.45E-11 32000

4 Stemwall 15 4.03E-13-1.93E-13 2700

5 Monolithic 4 2.79E-11-1.18E-11 10000

6 Monolithic 0 6.78E-12-1.46E-11 2100

7 Monolithic 2 9.18E-12-1.10E-11 11000

8 Step slabs 12 8.95E-12-1.51E-11 2700

9 Stemwall 0 4.OE-13-2.17E-11 1900

10 Stemwall 0 5.43E-10-1.13E-09 5000

11 Monolithic 0 9.63E-10-2.24E-10 1900

12 Stemwall 19 2.83E-10-1.25E-10 2800

13 Monolithic 19 3.12E-12-1.79E-11 1400

14 Stemwall 40 2.01E-13-2.58E-12 2800


1992)

















Table 4.2 Radon Test Results (Project of 1992)

House # Subslab Crack radon Indoor

radon (pCi/L) radon

(pCi/L) (pCi/L)

1 820 4 1.2

2 7800 N/A 11.58

3 1000 N/A 2.06

4 400 1 1.92

5 3700 N/A 3.51

6 860 N/A 0.56

7 3700 N/A 0.97

8 1600 7 1.71

9 1900 N/A 2.13

10 2200 N/A 2.52

11 760 N/A 1.61

12 2700 47 1.47

13 510 9 0.93

14 2100 5 2.66

Average 2146 12 2.49

N/A: not available




















Table 4.3 House Characteristics (Project of 1993)

House Degree of Foundation Total crack

# cracking type length (ft)

1 None Monolithic 0

2 Moderate Monolithic 2

3 Extensive Monolithic 42

4 None Monolithic 0

5 None Monolithic 0

6 Small Stemwall 9

7 Extensive Monolithic 182

8 Small Stemwall 26

9 Small Monolithic 10

10 None Monolithic 0

11 None Monolithic 0

12 None Monolithic 0








Table 4.4 Radon Test Results (Project of 1993)

House # Soil Crack Subslab Indoor

radon radon (Cch) radon (Cs) radon

(pCi/L) (pCi/L) (pCi/L) (pCi/L)

1 1683 N/A N/A 2.07

2 2935 180 639 2.99

3 1189 257 431 2.24

4 911 N/A N/A 2.7

5 2896 N/A N/A 2.52

6 1112 48 2934 4.16

7 921 23 931 N/A

8 6607 7 306 2.72

9 1298 12 1727 N/A

10 1055 N/A N/A 2.86

11 10661 N/A N/A 2.6

12 6982 N/A N/A N/A

Average 3188 40 2233 2.07

N/A: not available


Soil Data Analvsis


Soil radon gas is the main source of indoor radon

elevation. However, indoor radon levels are affected by a

complex of soil radon concentrations, soil permeability,

structural type, and construction quality. Regardless of

the combined effects of these parameters, indoor radon








levels are compared to soil gas radon and subslab radon

levels (combined data from 1992 and 1993 projects). A simple

linear regression analysis was performed using the following

model [Ott 1988, p.301-311]:

Y = Po + Pi log(x) + e

where Y = indoor radon

x = soil Radon or Subslab radon

P0 = Y intercept

Pi = slope of the regression line

s = random error.

Figure 4.1 illustrates the poor correlation between

indoor radon and soil radon. Figure 4.2 shows that indoor

radon and subslab radon are poorly correlated.





12

10- Y = 6.2451e-2 + 0.76772*LOG(x)
R^2 = 0.022

o4 8

0 6


4 4- +
0 4+
o +
+ +

+

0 10000 20000 30000 40000

Soil Radon (pCi/L)

Figure 4.1 Distribution of Indoor Radon versus Subslab Radon






77





12 +

y = 5.1416 + 2.4374*LOG(x)
2 10 R^2 = 0.233
-4
04 8-

0 6 -
4 4


0
0 + ++ +
2 +

++ + +

0 2000 4000 6000 8000 10000

Subslab Radon (pCi/L)

Figure 4.2 Indoor Radon versus Subslab Radon





Crack Study


This analysis is based on the project of the New House

Evaluation Program in 1993 [Hintenlang et al. 1994a]. The

crack study consisted of examining 12 new houses built in

the north central Florida area which are located in Alachua

and Marion counties. The purpose of the crack study is to

evaluate the contribution of cracks to the entry of radon

gas. Cracks are one of the most important physical

characteristics to consider in a foundation slab in reducing

indoor radon levels. If a large number of openings due to

cracks are present in a foundation slab, the soil gas radon

entering the building might elevate to an unacceptable








level. Therefore, it is necessary to identify and evaluate

the potential impact of cracks on radon entry.



Crack Research Process


The selected houses were checked for cracks one month

after the concrete slab was poured. The first step of the

crack study consisted of a visual inspection and crack

length measurement. After using a broom to brush away dirt

and construction materials, an optical comparator was used

to classify cracks according to their measured width. If

the crack length and width indicated more than surface

cracking, crack testing was performed. Cracks were

classified into four types: hairline, fine, medium, and

wide. The classification is shown in Table 4.5.



Table 4.5 Crack Classification

Crack Type Width (w) (inch)

Hairline w < 1/64

Fine 1/64 < w < 1/32

Medium 1/32 < w < 1/16

Wide 1/16 < w



All crack types were tested except the hairline crack.

The crack test consisted of two main parts: first, the

pressure differentials were measured as a function of the

flow rate through each crack using the permeameter; second,








radon concentration of the subslab soil gas extracted

through the crack was measured using the Pylon and

scintillation cells. A sniff measurement was taken on site

(to serve as a reference) and a grab count was measured from

this sample four hours later. The testing tube selected

should be located directly underneath the crack or as close

to the crack as possible. Subslab radon concentrations were

similarly measured after being extracted from sampling tubes

previously laid beneath the concrete slab.

The house dimensions, crack types, crack lengths, crack

locations, saw cuts and construction joints were documented

for each of the 12 houses. Figure 4.3 illustrates the crack

map of the house located at Summit Oaks. Refer this house

as Summit Oaks.


Data Analysis


Because NHEP-1992 and NHEP-1993 have different

mitigation methods and conditions, and the measurement

precision is different, only NHEP-1993 data were used in the

following analysis. The house data are shown in Table 4.6

and were analyzed statistically. The analyzed results are

listed in Table 4.7. Statistical analysis was performed

using SAS software. The first step consisted of testing the

normality of the data sets. The statistical analysis

indicated that the normalities of the data sets are high

(Refer to Appendix A). It is consequently assumed the data

sets are normal. The second step consisted of testing the








5.9 9.65---


Figure 4.3 Crack Map of House Summit Oaks


i
1.68

RF


6.30 I


Legend


Construction Joints:
Cracks: -
Drawing unit: meter


5.90


9.65








correlation between factors that might affect the entry of

indoor radon. The correlation model is [Ott 1988, p.319-

320] :

Y = Po + Pi x + S

where

Y = dependent variable

x = independent variable

P0, 41 = regression coefficients

e = random error.

Note:

r coefficient of determination

r = correlation coefficient.

For this analysis, the extreme data were taken out in

order to reduce variation between samples, such as the soil

radon of House Number 11 and the crack length of House

Number 7. The test results are shown in Table 4.8.



Correlation Analysis

The correlation analysis, as shown in Table 4.8,

indicates a low correlation between indoor radon levels and

crack parameters. However, there is a strong correlation (r2

= 0.94) between average indoor radon concentrations and

subslab soil radon concentrations.

This analysis only considered the correlation between

two data sets, i.e., the interrelationship with the third

data set was ignored.
















Table 4.6 House Characteristics

House # Crack TECA FOM CE (%)

Length(in) (Cch/Cs)

1 N/A N/A N/A N/A

2 24 5.4E-5 9.27E-3 28.17

3 132 1.68E-5 3.81E-3 60

4 N/A N/A N/A N/A

5 N/A N/A N/A N/A

6 108 6.23E-5 3.64E-6 1.64

7 1668 9.44E-6 2.83E-5 2.4

8 312 2.99E-4 2.03E-3 2.22

9 120 1.84E-5 2.21E-4 0.69

10 N/A N/A N/A N/A

11 N/A N/A N/A N/A

12 N/A N/A N/A N/A

Note: TECA: Total Equivalent Crack Area (in2)

FOG: Figure of Merit (pCi/L-in2

CE: Crack Efficiency (%')










Table 4.7 House Basic Statistics in the Crack Study

Variable Observa- Minimum Maximum Mean Standard

tions deviation

Crack length 11 0 312 63 99

(inch)

Soil radon 11 911 6607 2454 1470

(pCi/L)

Crack radon 12 0 227 40 78

(pCi/L)

Subslab 6 306 2394 1237 1185

radon

(pCi/L)


Table 4.8 Correlations between Factors

Correlation Indoor Soil Subslab Crack Crack

radon radon radon radon length

Indoor radon 1 -0.102 0.94 -0.02 0.14

Soil radon -0.102 1 -0.617 -0.173 0.587

Subslab 0.94 -0.617 1 -0.352 -0.307

radon

Crack radon -0.02 -0.173 -0.352 1 0.163

Crack Length 0.14 0.587 -0.307 0.163 1








Calculation of Crack Parameters


Crack parameters are defined as follows:

A = Q/(K x Ap)ln)

where K = 0.29, Ap = 4 pascal, Q = flow rate (m3/s) at

4 pascal, n = slope of log of flow rate vs. log of pressure

differentials (which can be found in the plot, refer to

Figure 4.4)

Total Equivalent Crack Area

= (A x Total Crack Length)/18.5 inch

Figure of Merit = Crack Radon x Total Equivalent Area

Crack Efficiency = Crack Radon /Subslab Radon x 100%


Comparison of Crack Characteristics with Indoor Radon


By comparing the average indoor radon and subslab radon

concentrations it was determined, as expected, that when

subslab radon increases, indoor radon increases as well. The

R2 was 0.88 as shown in Figure 4.5. It should be noted that

only four data sets were available for this analysis. In

Figure 4.6, the ratio of indoor radon and subslab radon is

compared to the total equivalent crack area (T.E.C.A). The

increase of T.E.C.A corresponds to an increase in the ratio

of indoor radon/subslab radon concentrations, which

indicates that crack openings do affect radon entry.


Potential Crack Radon Entry Analysis


By calculating the flow of soil gas entering the test










SUMMIT OAKS
LOT #13


19 1E-08 1E-07 1E-06
Flow Rate (Cu.M/S)


Type of Crack:
Total Crack Length:
Radon Conc. (crack):
Radon Conc. (sub-slab):

Q= 2.1E-09
n = 1.009


Fine
108
48.2
2934


in
(pCi/L)
(pCi/L)


(Cu.M/S)


A = Q/(Kx(Delta p) ^ n)
= 4.02E-10 Sq.M/L
= 6.23E-07 Sq. in/L


FLOW RATE PRESS. DIFF.
(Cu.M/S) (Pa)
1.67E-07 548
3.33E-07 623
4.17E-07 747
5E-07 996
5.83E-07 1096
6.67E-07 1245
7.5E-07 1444
8.3E-07 1544


Total Equivalent Crack Area
= (A x Total Crack Length) / 18.5 in
= 3.64E-06 Sq. in.

Figure of Merit
= Rn(crack) x Total Eq. Area
= 1.75E-04 (pCi/L)(Sq.in)

Crack Efficiency
= Rn(crack) / Rn(sub-slab)
1.64%


Figure 4.4 Calculation of Total Crack Equivalent Area