• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Acknowledgement
 Foreword
 Table of Contents
 Introduction
 Planning practices
 Erosion and sediment control...
 Stormwater runoff practices
 Estimating erosion on construction...
 Estimating runoff and stormwater...
 Appendices






Group Title: Virgin Islands environmental protection handbook
Title: Virgin Islands environmental protection handbook. 2002.
CITATION PDF VIEWER THUMBNAILS PAGE IMAGE ZOOMABLE
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STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/CA01300680/00001
 Material Information
Title: Virgin Islands environmental protection handbook. 2002.
Series Title: Virgin Islands environmental protection handbook
Physical Description: Serial
Language: English
Creator: University of the Virgin Islands. Cooperative Extension Service.
United States Virgin Islands. Department of Planning and Natural Resources. Nonpoint Source Pollution Management Program. ( Contributor )
Affiliation: University of the Virgin Islands -- Cooperative Extension Service
Publisher: University of the Virgin Islands. Cooperative Extension Service.
Publication Date: 2002
 Subjects
Subject: Caribbean   ( lcsh )
Spatial Coverage: North America -- United States Virgin Islands
Caribbean
 Record Information
Bibliographic ID: CA01300680
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Title Page
    Acknowledgement
        Acknowledgement
    Foreword
        Foreword 1
        Foreword 2
    Table of Contents
        Page i
        Page ii
        Page iii
        Page iv
        Page v
        Page vi
    Introduction
        Page 1-i
        Page 1-ii
        Introduction
            Page 1-1
        Stormwater runoff, erosion and sedimentation processes
            Page 1-2
            Page 1-3
            Page 1-4
        Pollutants and their impacts
            Page 1-5
        Proper planning
            Page 1-6
        Organization of this handbook
            Page 1-7
        Purpose of this handbook
            Page 1-8
        References
            Page 1-8
            Page 1-9
            Page 1-10
    Planning practices
        Page 2-i
        Page 2-ii
        Planning - The basis of smart development
            Page 2-1
        Know your soils
            Page 2-1
        Watershed planning
            Page 2-2
        Site planning practices
            Page 2-3
            Page 2-4
            Page 2-5
        Development planning practices
            Page 2-6
            Page 2-7
            Page 2-8
        Good housekeeping practices
            Page 2-9
            Page 2-10
            Page 2-11
            Page 2-12
        Conclusion
            Page 2-13
        References
            Page 2-13
            Page 2-14
    Erosion and sediment control practices
        Page 3-i
        Page 3-ii
        Introduction
            Page 3-1
        Stabilization practices
            Page 3-2
            Page 3-3
            Page 3-4
            Page 3-5
            Page 3-6
            Page 3-7
            Page 3-8
            Page 3-9
            Page 3-10
            Page 3-11
            Page 3-12
            Page 3-13
            Page 3-14
            Page 3-15
            Page 3-16
            Page 3-17
            Page 3-18
        Structural practices
            Page 3-19
            Page 3-20
            Page 3-21
            Page 3-22
            Page 3-23
            Page 3-24
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            Page 3-26
            Page 3-27
            Page 3-28
            Page 3-29
            Page 3-30
            Page 3-31
            Page 3-32
            Page 3-33
            Page 3-34
        References
            Page 3-35
            Page 3-36
    Stormwater runoff practices
        Page 4-i
        Page 4-ii
        Introduction
            Page 4-1
        Filtration practices
            Page 4-1
            Page 4-2
            Page 4-3
            Page 4-4
            Page 4-5
            Page 4-6
            Page 4-7
        Detention practices
            Page 4-8
            Page 4-9
            Page 4-10
        Infiltration practices
            Page 4-11
            Page 4-12
            Page 4-13
            Page 4-14
            Page 4-15
            Page 4-16
        References
            Page 4-17
            Page 4-18
    Estimating erosion on construction sites using the revised universal soil loss equation (RUSLE)
        Page 5-i
        Page 5-ii
        Introduction
            Page 5-1
        Review of RUSLE and factors
            Page 5-2
        Examples of how the revised universal soil loss equation (RUSLE) is used
            Page 5-3
        Tables
            Page 5-4
            Page 5-5
            Page 5-6
            Page 5-7
            Page 5-8
            Page 5-9
            Page 5-10
            Page 5-11
        References
            Page 5-12
    Estimating runoff and stormwater discharge
        Page 6-i
        Page 6-ii
        Introduction
            Page 6-1
        Estimating runoff - the SCS curve number method
            Page 6-1
            Page 6-2
            Page 6-3
            Page 6-4
            Page 6-5
            Page 6-6
        Time of concentration and travel time
            Page 6-7
            Page 6-8
            Page 6-9
            Page 6-10
        Graphical peak discharge method
            Page 6-11
        TR-55 worksheet solutions to examples
            Page 6-12
            Page 6-13
            Page 6-14
            Page 6-15
            Page 6-16
            Page 6-17
            Page 6-18
        Figures and tables
            Page 6-19
            Page 6-20
            Page 6-21
            Page 6-22
            Page 6-23
            Page 6-24
            Page 6-25
            Page 6-26
            Page 6-27
            Page 6-28
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            Page 6-30
            Page 6-31
            Page 6-32
            Page 6-33
            Page 6-34
            Page 6-35
            Page 6-36
        References
            Page 6-37
            Page 6-38
            Page 6-39
            Page 6-40
    Appendices
        Page Appendix 1
        Page Appendix 2
        Appendix A: Glossary
            Page A-1
            Page A-2
            Page A-3
            Page A-4
            Page A-5
            Page A-6
            Page A-7
            Page A-8
        Appendix B: Erosion and sediment control practice specifications
            Page B-i
            Page B-ii
            Page B-1
            Page B-2
            Page B-3
            Page B-4
            Page B-5
            Page B-6
            Page B-7
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            Page B-87
            Page B-88
            Page B-89
            Page B-90
        Appendix C: Stormwater practice specifications
            Page C-i
            Page C-ii
            Page C-1
            Page C-2
            Page C-3
            Page C-4
            Page C-5
            Page C-6
            Page C-7
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            Page C-25
            Page C-26
            Page C-27
            Page C-28
        Appendix D: Environmental protection laws
            Page D-i
            Page D-ii
            Page D-1
            Page D-2
            Page D-3
            Page D-4
            Page D-5
            Page D-6
            Page D-7
            Page D-8
        Appendix E: References
            Page E-1
            Page E-2
            Page E-3
            Page E-4
            Page E-5
            Page E-6
Full Text



VIRGIN ISLANDS
ENVIRONMENTAL PROTECTION
HANDBOOK

2002


Published by the University of the Virgin Islands Cooperative Extension Service
Funded by a federal Clean Water Act grant from the Virgin Islands Department of Planning and Natural
Resources 319(h) Nonpoint Source Pollution Management Program.







VIRGIN ISLANDS
ENVIRONMENTAL PROTECTION
HANDBOOK

2002


Published by the University of the Virgin Islands Cooperative Extension Service and
Funded by a federal Clean Water Act grant from the Virgin Islands Department of Planning and Natural
Resources 319(h) Nonpoint Source Pollution Management Program.








VIRGIN ISLANDS
ENVIRONMENTAL
PROTECTION
HANDBOOK


2002





A GUIDE TO ASSIST IN THE IMPLEMENTATION OF ENVIRONMENTAL
PROTECTION LAWS OF THE UNITED STATES VIRGIN ISLANDS


Original Document by the
Virgin Islands Conservation District
1976


Virgin Islands Nonpoint Source Pollution Control Committee Second Revision 1995


University of the Virgin Islands Cooperative Extension Service
Third Revision 2002


Funded by a grant from the Virgin Islands Department of Planning and Natural Resources 319(h)
Nonpoint Source Pollution Management Program.















ACKNOWLEDGMENTS


Environmental Protection Handbook Revision Workgroup:
K. Olasee Davis, Natural Resources Specialist, UVI-CES
Dr. Barry Devine, Chief Scientist, UVI-ECC
William F. McComb, McComb Engineering
Rudy G. O'Reilly, Jr., District Conservationist, USDA-NRCS
Carlos Ramos, Island Resources Foundation, Inc.
Bill Rohring, GIS Coordinator, DPNR-CZM
Dr. Henry H. Smith, Director, WRRI
Mayra Suirez-V6lez, Marine Advisor, UVI-CMES
Marcia Taylor, Marine Advisor, UVI-CMES
Julie A. Wright, Natural Resources Program Supervisor, UVI-CES





2002Virgin Islands Environmental Protection Handbook Principal Writer and Editor:
Julie A. Wright, Natural Resources Program Supervisor
University of the Virgin Islands, Cooperative Extension Service



Other Written Contributions By:
James G. Bernier, former Director, Division of Permits, DPNR;
Maria Montes, Agronomist, USDA Natural Resources Conservation Service;
and
Mario A. Morales, former RC&D Coordinator, Virgin Islands Resource Conservation and
Development Council, Inc./USDA-NRCS










FOREWORD


The Virgin Islands Nonpoint Source (NPS) Pollution Control Committee was formed in the fall of 1992 to
address nonpoint pollution problems in Virgin Islands' waters. Nonpoint source pollution of water resources
comes from many sources and is caused by rainfall moving over and through the ground. As the rainwater moves,
it picks up and carries away both natural and man-induced pollutants. These pollutants are then deposited onto
roadways and downhill properties, and into guts, ponds wetlands, ground water, and coastal waters. Nonpoint
source pollution in the Virgin Islands is commonly associated with land management practices involving
construction, urban runoff, failing septic systems, marina operations, agriculture and hydrologic modification.

The NPS Committee receives funding from the U.S. Environmental Protection Agency through grants to
implement the provisions of Section 319 of the U.S. Clean Water Act and Section 6217(g) of the U.S. Coastal
Zone Act Reauthorization Amendments. Part of this federal funding was allocated to revise the Environmental
Protection Handbook in order to conform with the intent of federal legislation.

The Environmental Protection Handbook is intended for use only as a guide to the reader, indicating what
practices, standards, and procedures should be utilized in the development planning process in order to comply
with the Virgin Islands Environmental Protection Law, Title 12, Chapter 13 of the Virgin Islands Code and the
corresponding Virgin Islands Rules and Regulations. It is designed to assist contractors, developers, architects,
and home builders implement a Stormwater, Erosion and Sediment Control Plan specifically designed for their
construction site.

This handbook provides useful information on stormwater, erosion, and sediment control practices that can be
used to prevent or reduce the discharge of sediment and other pollutants in stormwater runoff from your
construction site. It also describes the practices and controls, and details how, when and where these practices
are applicable. However, careful consideration must be given to selecting the most appropriate control measures
based on site-specific conditions, and on properly installing the controls in a timely manner.

Lack of description or criteria for a specific practice does not suggest it should not be used, but only that
consideration by the appropriate reviewing agency will be on the basis of information submitted with the design.

The term "shall" is used where the practice is sufficiently standardized to permit specific delineation of
requirements or where safe-guarding of the public health or protection of water quality justifies such definite
action. Other terms, such as "should" or "recommended" or "preferred" indicate desirable procedures or
methods, with deviations subject to individual consideration.











The Virgin Islands Environmental Protection Handbook is published by the University of the .... Islands, Cooperative
Extension Service. Contents of this publication constitute public property. No endorsement ofproducts orfirms is intended nor is
criticism implied of those not mentioned. Issued by the -, ... Islands Cooperative Extension Service and the U.S. Department of
Agriculture infurtherance of the Acts ofMay 8 and June 30, 1914. Extension programs and policies are consistent with federal
and state laws and .. *.! ; .... on non-discrimination ... ., I... race, color, national origin, .. ....... gender, age, disability, and
gender preference.







Table of Contents


ENVIRONMENTAL PROTECTION HANDBOOK
TABLE OF CONTENTS


CHAPT


Environmental Protection Handbook I


ER 1: INTRODUCTION ..........................................................

1.1 INTRODUCTION ..........................................................

1.2 STORMWATER RUNOFF, EROSION AND SEDIMENTATION PROCESSES ............

1.2.1 Storm w ater Runoff ...................................................
1.2.2 Changes in H ydrology .................................................
1.2.3 Erosion ...................................... ......................
1.2.4 Sedimentation .......................................................

1.3 POLLUTANTS AND THEIR IMPACTS .........................................

1.3.1 Sedim ent ...........................................................
1.3.2 Nutrients ...........................................................
1.3.3 Oxygen-dem ending Substances ..........................................
1.3.4 Bacteria, Viruses and Other Pathogens .....................................
1.3.5 Petroleum Hydrocarbons (Oil and Grease) .................................
1.3.6 Heavy M etals and Toxic Substances .......................................
1.3.7 O their Im pacts ......................................................

1.4 PRO PER PLAN N IN G .......................................................

1.4.1 Land is a Lim ited Resource .............................................
1.4.2 Know Your Soil ......................................................

1.5 ORGANIZATION OF THIS HANDBOOK .......................................

1.6 PURPOSE OF THIS HANDBOOK .............................................

1.7 REFERENCES .............................................................

ER 2: PLANNING PRACTICES .....................................................

2.1 PLANNING THE BASIS OF SMART DEVELOPMENT ............................

2.2 KN OW YO U R SO ILS .......................................................

2.3 W ATERSHED PLANNING ...................................................

2.4 SITE PLANNING PRACTICES ................................................

2.5 DEVELOPMENT PLANNING PRACTICES ......................................


CHAPT







Table of Contents

2.5.1 Pollution Prevention Management Plan .................................... 2-6

2.6 GOOD HOUSEKEEPING PRACTICES ......................................... 2-9

2.6.1 W aste D isposal ...................................................... 2-9

2.6.1.a Construction W astes ............................................ 2-9
2.6.1.b H hazardous Products ........................................... 2-10

2.6.2 M material M anagem ent ................................................ 2-10

2.6.2.a Pesticides ................................................... 2-11
2.6.2.b Petroleum Products ........................................... 2-11
2.6.2.c Fertilizers/D etergents ........................................ .. 2-12

2.6.3 Spills ...................................... ....................... 2-12

2.7 CONCLUSION ........................................................... 2-13

2.8 REFERENCES ............................................................ 2-13

CHAPTER 3: EROSION AND SEDIMENT CONTROL PRACTICES ............................... 3-i

3.1 INTRODUCTION ............................................................. 3-1

3.2 STABILIZATION PRACTICES .................................................... 3-2

Preservation and Protection of Natural Vegetation .................................. 3-3
Filter Strips ............................................................. 3-5
Land Grading .............................................................. 3-6
Surface Roughening ................... ................... ................... 3-7
Tem porary Seeding ......................................................... 3-8
Permanent Seeding and Planting ............................................... 3-10
M ulches, M ats and Geotextiles ................................................ 3-11
Soil Binders/Tackifiers ...................................................... 3-14
Soil Retaining W alls ...................................... .................. 3-15
Soil Bioengineering ........................................................ 3-16

3.3 STRUCTURAL PRACTICES .................................................. ..3-19

Perim eter D ikes and Sw ales .................................................. 3-19
Drainage Swales ...................................... ..................... 3-20
Temporary Storm Drain Diversion ............................................. 3-21
Silt Fence ................................................................ 3-22
Gravel/Stone Filter Berm .................................................... 3-24
Stabilized Construction Entrance .............................................. 3-24
Check Dams/Triangular Dikes/Berms ........................................... 3-25
Sediment Traps ...................................... ..................... 3-27


II Environmental Protection Handbook







Table of Contents

Tem porary Sedim ent Basin ................................................... 3-30
Storm D rain Inlet Protection ................................................. 3-31
Outlet Protection .......................................................... 3-33
Gabion Inflow Protection .................................................... 3-34

3.4 REFERENCES .............................................................. 3-35

CHAPTER 4: STORMWATER RUNOFF PRACTICES .......................................... 4-i

4.1 INTRODUCTION .......................................................... 4-1

4.2 FILTRATION PRACTICES ................................................... 4-1

Buffer Zones .................................... .......................... 4-2
Grassed Swales ............................................................. 4-4
Sand Filters ............................................................. 4-5
W ater Quality Inlets ......................................................... 4-7

4.3 DETENTION PRACTICES ................................................... 4-8

Extended Detention Ponds .................................................... 4-8
Constructed W wetlands ...................................................... 4-10

4.4 INFILTRATION PRACTICES ................................................ 4-11

Porous Pavers ............................................................. 4-11
Infiltration Trenches ....................................................... 4-12
B io-R detention ............................................................ 4-15

4.5 REFERENCES ............................................................ 4-17

CHAPTER 5: ESTIMATING EROSION ON CONSTRUCTION SITES USING THE REVISED UNIVERSAL
SOIL LOSS EQUATION (RUSLE) .............................................. 5-i

5.1 INTRODUCTION .......................................................... 5-1

5.2 REVIEW OF RUSLE AND FACTORS ........................................... 5-2

5.3 EXAMPLES OF HOW THE REVISED UNIVERSAL SOIL LOSS EQUATION (RUSLE) IS USED
. . . . . . . . . . . . . . . . . . . 5 -3


5.3.1 Example 1 ...................................... ...................... 5-3
5.3.2 Example 2 ...................................... ...................... 5-3
5.3.3 Example 3 ...................................... ...................... 5-4
5.3.4 Example 4 ............................................................ 5-4

5.4 TABLES .................................................................. 5-4



Environmental Protection Handbook III







Table of Contents


Table 5.1. Soil Erodibility Factors (K), Soil Loss Tolerance Factors (T), and Hydrologic Soil Groups
of the A, B and C Horizons, U.S. Virign Islands Soil Series ............................ 5-4
Table 5.2.a. Topographic Adjustment Factors (LS) for Slope Percent and Slope Length ...... 5-7
Table 5.2.b. Topographic Adjustment Factors (LS) for Slope Percent and Slope Length ...... 5-8
Table 5.2.c. Topographic Adjustment Factors (LS) for Slope Percent and Slope Length ...... 5-9
Table 5.3. Cover Index Factor (C) for Construction Sites ............................ 5-10
Table 5.4. Practice Factor (P) for Surface Conditions for Construction Sites ............. 5-10
Table 5.5. Adjustment Factors (M) for Estimating Monthly and Portions of Annual Soil Loss 5-11
Table 5.6. Approximate Soil Weights in Pounds per Cubic Foot and Conversion Factors .... 5-11
Table 5.7. USDA Texture Abbreviations ........................................ 5-12

5.5 REFERENCES ............................................................ 5-12

CHAPTER 6: ESTIMATING RUNOFF AND STORMWATER DISCHARGE

6.1 INTRODUCTION ............................................................. 6-1

6.2 ESTIMATING RUNOFF THE SCS CURVE NUMBER METHOD ....................... 6-2

6.2.1 Factors Considered in Determining Runoff Curve Numbers ....................... 6-3

6.2.1.a Hydrologic Soil Groups .......................................... 6-3
6.2.1.b CoverType .................................................. 6-4
6.2.1.c Treatm ent ................................................... 6-4
6.2.1.d Hydrologic Condition ........................................... 6-4
6.2.1.e Antecedent Runoff Condition ..................................... 6-4
6.2.1.f Urban Impervious Area Modifications ................................ 6-4
6.2.1.g Connected Impervious Areas ...................................... 6-4
6.2.1.h Unconnected Impervious Areas .................................... 6-5
6.2.1.i Rainfall ....................................................... 6-5
6.2.1.j Runoff ........................................... .......... 6-5

6.2.2 Lim stations ......................................................... .. 6-5
6.2.3 Examples ............................................................ 6-6

6.2.3.a Example 1 .................................................... 6-6
6.2.3.b Example 2 .................................................... 6-7
6.2.3.c Example 3 .................................................... 6-7
6.2.3.d Exam ple 4 .................................................... 6-8

6.3 TIME OF CONCENTRATION AND TRAVEL TIME ................................... 6-8

6.3.1 Factors Affecting Time of Concentration and Travel Time ........................ 6-9

6.3.1.a Surface Roughness .............................................. 6-9
6.3.1.b Channel Shape and Flow Patterns .................................. 6-9
6.3.1.c Slope ........................................................ 6-9



IV Environmental Protection Handbook







Table of Contents


6.3.2 Computation of Travel Time and Time of Concentration ......................... 6-9
6.3.3 Sheet flow ........................................................... 6-10
6.3.4 Shallow Concentrated Flow .............................................. 6-10
6.3.5 Open Channels ....................................................... 6-11
6.3.6 Reservoirs, Lakes or Ponds .............................................. 6-11
6.3.7 Limitations .......................................................... 6-11
6.3.8 Example 5 ........................................................... 6-11

6.4 GRAPHICAL PEAK DISCHARGE METHOD ........................................ 6-12

6.4.1 Peak Discharge Computation ............................................. 6-13
6.4.2 Lim stations ......................................................... 6-13
6.4.3 Exam ple 6 ........................................................... 6-13
6.5 TR-55 WORKSHEET SOLUTIONS TO EXAMPLES ................................. 6-13

6.6 FIGU RES AND TABLES ....................................................... 6-20

Figure 6.1. Solution of runoff equation for SCS curve number method ................. 6-20
Figure 6.2. Flow chart for selecting appropriate figure or table for determining runoff curve
num bers ................................................................. 6-21
Table 6.1. Runoff depth for selected curve numbers (CN's) and rainfall amounts .......... 6-22
Table 6.2.a. Runoff curve numbers for urban areas ................................ 6-23
Table 6.2.b. Runoff curve numbers for cultivated agricultural lands .................... 6-24
Table 6.2.c. Runoff curve numbers for other agricultural lands ........................ 6-25
Table 6.2.d. Runoff curve numbers for arid and semiarid rangelands ................... 6-26
Table 6.3. Hydrologic soil groups of the U.S. Virgin Islands .......................... 6-26
Figure 6.3. Composite CN with connected impervious area .......................... 6-27
Figure 6.4. Composite CN with unconnected impervious areas and total impervious area less than
30% ................... ............................................... 6-27
Figure 6.5. 1-year, 24-hour rainfall for the U.S. Virgin Islands ........................ 6-28
Figure 6.6. 2-year, 24-hour rainfall for the U.S. Virgin Islands ................... ..... 6-28
Figure 6.7. 5-year, 24-hour rainfall for the U.S. Virgin Islands ........................ 6-29
Figure 6.8. 10-year, 24-hour rainfall for the U.S. Virgin Islands ....................... 6-29
Figure 6.9. 25-year, 24-hour rainfall for the U.S. Virgin Islands ....................... 6-30
Figure 6.10. 50-year, 24-hour rainfall for the U.S. Virgin Islands ...................... 6-30
Figure 6.11. 100-year, 24-hour rainfall for the U.S. Virgin Islands ..................... 6-31
Table 6.4. Roughness coefficients (Manning's n) for sheet flow ....................... 6-31
Table 6.5. I, values for runoff curve numbers ..................................... 6-32
Figure 6.12. Ai. ~i g. velocities for estimating travel time for shallow concentrated flow ..... 6-33
Figure 6.13. Unit peak discharge for SCS type-III rainfall distribution .................. 6-34
Table 6.6. Adjustment factor for pond and swamp areas that are spread throughout the watersh6i35

6.7 REFERENCES .............................................................. 6-35

APPENDICES

APPENDIX A: GLOSSARY ................................................................ A-i


Environmental Protection Handbook V







Table of Contents

APPENDIX B: EROSION AND SEDIMENT CONTROL PRACTICE SPECIFICATIONS .................. B-i

Preservation and Protection of Natural Vegetation ......................................... B-1
Filter Strips .................................................................... B-3
Land Grading ...................................... .............................. B-5
Surface Roughening ......................................................... ...... B-7
Temporary Seeding ................................................................ B-9
Perm anent Seeding and Planting ..................................................... B-13
M ulches, M ats and Geotextiles ...................................................... B-15
Soil Retaining W alls ...................................... ........................ B-19
Soil Bioengineering ............................................................... B-27
Perimeter Dikes and Swales ......................................................... B-33
Drainage Swales ...................................... ........................... B-35
Tem porary Storm Drain Diversion ................................................... B-37
Silt Fence ...................................... ................... ............. B-39
Stabilized Construction Entrance ..................................................... B-41
Check Dams ............ ................................................... B-43
Sediment Trap .................................................................. B-45
Temporary Sediment Basin ......................................................... B-53
Storm Drain Inlet Protection ....................................................... B-75
Outlet Protection ...................................... .......................... B-79
Gabion Inflow Protection ......................................................... B-87
References .................................................................... B-89

APPENDIX C: STORMWATER PRACTICE SPECIFICATIONS .................................... C-i

Buffer Zones ..................................................................... C-1
Grassed Swales ......................................................... .......... C-3
Sand Filters .................................................................... C-5
W ater Quality Inlets ......................................................... ...... C-7
Extended Detention Ponds .......................................................... C-9
Constructed W wetlands ............................................................. C-13
Porous Pavers ......................................................... .......... C-17
Infiltration Trenches .............................................................. C-21
Bio-Retention ................................................................... C-25
References .................................................................... C-27

APPENDIX D: ENVIRONMENTAL PROTECTION LAWS ....................................... D-l

APPENDIX E: REFERENCES .............................................................. E-l


VI Environmental Protection Handbook







Chapter 1 Introduction

CHAPTER 1: BACKGROUND
TABLE OF CONTENTS




1.1 INTRODUCTION ................ ............................ ........... 1-1

1.2 STORMWATER RUNOFF, EROSION AND SEDIMENTATION PROCESSES ............ 1-2

1.2.1 Storm w ater Runoff ................................................... 1-2
1.2.2 Changes in H ydrology ................................................. 1-3
1.2.3 Erosion ............................................................ 1-4
1.2.4 Sedim entation ....................................................... 1-4

1.3 POLLUTANTS AND THEIR IMPACTS ................................... .. 1-5

1.3.1 Sediment ........................................................... 1-5
1.3.2 Nutrients ........................................................... 1-5
1.3.3 Oxygen-demanding Substances .......................................... 1-6
1.3.4 Bacteria, Viruses and Other Pathogens ..................................... 1-6
1.3.5 Petroleum Hydrocarbons (Oil and Grease) ................................. 1-6
1.3.6 Heavy Metals and Toxic Substances ...................................... 1-6
1.3.7 Other Impacts ....................................................... 1-6

1.4 PRO PER PLAN NING ....................................................... 1-6

1.4.1 Land is a Limited Resource ............................................. 1-6
1.4.2 Know Your Soil ...................................................... 1-7

1.5 ORGANIZATION OF THIS HANDBOOK .................................... 1-7

1.6 PURPOSE OF THIS HANDBOOK .......................................... ..1-8

1.7 REFERENCES ........................................................... 1-8


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Introduction


1-ii Environmental Protection Handbook


Chapter 1







Introduction


CHAPTER 1: BACKGROUND


1.1 INTRODUCTION

Increasing amounts of forest and grass lands in the U.S. Virgin Islands are being converted to housing, roads, and
commercial and industrial land uses each year. These construction activities take place on many different kinds of
topography and soils, each having different properties and limitations. Such activities and land uses alter natural water
flow paths and seepage of water into the soil (change hydrology) and increase erosion and sedimentation, damaging the
environment. Ecosystem degradation also results from poor land clearing and landscaping practices that negatively impact
plants, wildlife, soil, and water resources. Large-scale removal of vegetation reduces wildlife habitat, promotes soil erosion
and sedimentation, and threatens biological diversity. Construction along ridge lines and in guts (intermittent streams)
is rapidly depleting moist forest habitat and changing microclimates in the territory.

Increased runoff causes severe erosion and more frequent flooding and has created serious problems in many areas of
the Virgin Islands. Eroding road beds and cut slopes (e.g. behind houses or next to roads) cause costly property damage.
Sediment and other pollutants run off uphill construction sites, roads, parking lots and other land areas and are deposited
along roadways, in guts, on lower-lying property, and in ponds and coastal waters, polluting surface and ground water.

Decreased water seepage into the ground (infiltration) also reduces the islands' critical fresh water supply. As paved areas
increase, the amount of rainfall that seeps into the soil and into ground water is decreased. This reduces the water
available for plant growth and as ground water for public consumption. In order to provide fresh water to the growing
population of the Virgin Islands, and to ensure healthy terrestrial ecosystems, it is critical to retain as much rainwater as
possible within the ground, in guts and in other surface water bodies.

The beauty and health of the Virgin Islands' environment is vital to the health and well being of all Virgin Islanders. Many
residents enjoy the islands' beaches and coastal waters for swimming, bathing, snorkeling, diving, sailing, and fishing. The
Virgin Islands fishing industry depends upon healthy coastal waters and reefs for its livelihood. Many residents also use
native plants for cultural or medicinal purposes. However, these uses and environmental health, in general, are often
considered to be secondary to the development process. Ugly raw excavation scars remain long after land development
has been completed. Coastal water quality has been steadily deteriorating due to the influx of sediment, sewage and other
pollutants. The health of the coral reefs is correspondingly declining. Many native plants and animals have become rare,
threatened or endangered. This degradation is a long-term threat to the Virgin Islands economy, especially since that
economy is dependent upon its environmental health and beauty to attract tourism, the largest industry.

Concern for the environment, including plant, soil and water resources, was made a matter of public policy through
passage of the Soil and Water Conservation District Law and the Environmental Protection Law of 1971, as amended.
The Environmental Protection Program, overseen by the Virgin Islands Department of Planning and Natural Resources
(DPNR), promulgates rules and regulations in accordance with the Environmental Protection Law in order to "...prevent
improper development of land and harmful environmental changes" (VIDCCA, 1979). This Program includes comprehensive
erosion and sediment control measures applicable to both public and private developments, including the construction
and maintenance of streets and roads. These rules and regulations are modified as necessary to meet the requirements
of new Federal Programs.


Environmental Protection Handbook 1-1


Chapter 1







Introduction


1.2 STORMWATER RUNOFF, EROSION AND SEDIMENTATION PROCESSES

Stormwater runoff and erosion are natural processes that occur in the environment. However, as human activities alter
the landscape, adverse impacts to receiving waters i'.ult, ponds, bays and other coastal areas) may result from changes
in the quantity and quality of stormwater runoff. If left unmanaged, the hydraulic impacts (flooding, erosion,
channelization) associated with increased stormwater runoff can be significantly higher than that of undisturbed areas.
In addition to causing flooding, this stormwater is also a major nonpoint (diffuse) pollution source.

Nonpoint source pollution of water resources comes from many sources and is caused by rainfall moving over and through
the ground. As the rainwater moves, it picks up and carries away pollutants such as sediment, excess nutrients, bacteria
and other pathogens, oil and grease, and other toxic materials. These pollutants are then deposited onto roadways and
downhill properties, and into guts, ponds wetlands, ground water, and coastal waters. Nonpoint source pollution in the
Virgin Islands results from construction activities, urban runoff, failing septic systems, marina and recreational boating
operations, and agriculture.

Urbanization (the conversion of rural areas or open spaces to suburban, commercial, or industrial land uses) typically
results in changes to the physical, chemical, and biological characteristics of a watershed (or drainage basin). A watershed
is the area of land that drains water, sediment, and other pollutants to a common outlet along the coastline (bay, lagoon
or other coastal area, see Figure 1.1). The physical processes by which construction and other urban activities adversely
affect water volumes and quality are stormwater runoff, erosion and sedimentation. Each of these processes has different
impacts upon receiving waters.


/Drainage basin boundaries (or divides) rious sized watersheds: sub-basin divide/
(left) main \ rshed delineation
I









S/Ground
S, -
\ .4






Y ./ *" .. Drainage basin boundaries (or divides)for various sized watersheds: sub-basin divide
(left) main watershed delineation 4,; ,, .

Gut or drainage channel

Watershed (or basin) outlet

Groundwater '..ii

Figure 1.1. Watersheds (or drainage basins) and their boundaries (Dunne and Leopold, 1978).



1.2.1 Stormwater Runoff

Natural vegetated and open forest areas are pervious areas under natural conditions, rainwater that falls on these areas
seeps into the soil and does not run over the land surface. Vegetation (trees, grasses, bushes and other ground covers)


1-2 Environmental Protection Handbook


Chapter 1









slows rainfall, natural depressions temporarily hold water, and the humus layer of the forest floor absorbs rainfall. Plants
also reduce raindrop impacts on the soil surface, reducing the detachment and erosion of soil particles through raindrop
splashing (Donahue, Miller, and Shickluna, 1983). During development and urbanization, however, the soil's plant cover
and humus layer are stripped from the land by clearing and grading. These activities increase the amount of rainwater
that runs off the land surface as stormwater runoff. When pervious areas are converted to impervious land uses (housing,
roads, parking lots, or commercial areas) the amount of vegetation (and therefore the perviousness of the land) is
decreased and stormwater runoff volume and velocity increases. Therefore, rain falling onto the surface of unmanaged,
urbanizing watersheds results in a predictable increase in the quantity of runoff flowing to coastal waters (see Figure 1.2).


S 20% Runoff


38% Evapotranspiration


ration


21% Shallow 21% Deep Infilt
Infiltration 0 o
Oo 0 0

0 o a 0 o ao 0
10 TO 20% IMPERVIOUS SURFACE


NATURAL GROUND COVER


20% Shallow 0 O 15% Deep Infl
Infiltration 0 0 Oo 0
I o Do o" o 0
00 -4 Oo

00o 0 O o 0
30 TO 35% IMPERVIOUS SURFACE


10% Shallow |/ 'V 5% Deep Infiltration
Infllration 7 o
0 0 0,07 0 do
S0 0
0 a o


75 TO 100% IMPERVIOUS SURFACE


Figure 1.2. Water cycle changes associated with urbanization and resulting increases in impervious surfaces (Arnold & Gibbons, 1998).



1.2.2 Changes in Hydrology

The great increase in stormwater runoff due to urbanization changes the hydrology, or the natural water movement, of
the watershed. Hydrologic changes in watershed are ng ,i7f i.. i after the completion of construction. Impervious surfaces
prevent rain seepage into the soil, resulting in much increased volumes and speed (rate or velocity) of runoff. Control
of higher stormwater flows requires the construction or "improvement" of runoff culverts, swales or other stormwater
channels or the modification of existing drainage systems to avoid erosion of gut banks and steep slopes. The hydrologic
changes in drainage channels or natural guts resulting from urbanization include:



Environmental Protection Handbook 1-3


--~i~ii~ii~ii~i~7~?i~~


Chapter 1


Introduction







Introduction


Increased peak runoff discharges two to five times pre-development levels;
Increased volume of stormwater runoff produced by storms (a moderately developed watershed can produce
50% more runoff than a forested watershed during the same storm);
Increased frequency and severity of flooding;
Greater runoff velocity during storms; and
Reduced water levels in soils, guts, and aquifers due to the reduced level of infiltration in the watershed. This
change in the hydrologic cycle (Figure 1.3) can result in microclimate change in small, insular, tropical island
ecosystems, such as the Virgin Islands.


Figure 1.3. The hydrologic cycle (modified from Dunne and Leopold, 1978).


1.2.3 Erosion

Increased stormwater runoff volume and velocity results in increased erosion. Water erosion is the loosening and removal
of soil particles from the land surface by running water. The rate of erosion is directly related to stormwater runoff
velocity and volume. There are many different types of erosion: raindrop, sheet, rill, gully, and stream channel erosion.
Removal of vegetation from the land surface during construction and other land-clearing activities increases all these types
of erosion. (Erosion can also be caused by wind many wind erosion control practices are similar to water erosion
control practices.)

The primary factors affecting erosion are rainfall intensity and frequency, soil characteristics, vegetative and other surface
cover, topography (slope), climate, and aspect (i.e., degree of exposure to sun and tradewinds). Rainfall intensity (the
volume of rainfall in a given time period) and slope steepness are the most significant factors affecting erosion. Soil
physical factors (texture, structure) that affect infiltration capacity and soil detachment and transport are also important.
Plants help to reduce erosion by intercepting rainfall and reducing raindrop energy, slowing runoffvelocity, holding soil
in place with roots, and improving soil porosity.

1.2.4 Sedimentation

Sedimentation occurs when eroded soil particles suspended in stormwater runoff are deposited onto flood plains,
roadways or downhill properties, or into guts, ponds and coastal waters. Sediment can travel either suspended in runoff


1-4 Environmental Protection Handbook


___ ) c. -.^ '- -,---
IIt' "r t r I r :
11i/ J Jnfq# 0


Pr la. tEvaporation
unoff Interception
Percolation /
SIn iltration / iao
^f Transp iration


Guts


Chapter 1









water or it can travel along the ground surface or the bottom of a channel or gut. Suspended sediment in stormwater
runoff is the largest pollutant, byvolume, in Virgin Islands' waters. Factors affecting sedimentation include runoffvelocity,
soil particle size, drainage channel roughness, and flow obstructions. Obstructions in the path of runoff water and rough
channels slow runoff, causing sediment to settle to the bottom of the channel, gut or pond. Soil particle size and weight
also affect sedimentation: finer particles (clays) will stay suspended in runoff water for a longer period of time and will
travel farther than larger, heavier particles (like sands).

1.3 POLLUTANTS AND THEIR IMPACTS

As the population density of an area increases, there is a corresponding increase in pollutant loadings generated from
human activities. Pollutant export increases dramatically both during and after development. During construction, soils
are exposed and large amounts of sediment, along with attached soil nutrients and other pollutants, can run off into
surface waters if proper erosion and sedimentation controls are not used. Once a construction site is stabilized, pollutants
accumulate rapidly on impervious surfaces and are easily washed off. The primary pollutant carried by stormwater runoff
is sediment. However, many other pollutants are transported to coastal waters by stormwater runoff: excess nutrients,
harmful bacteria and viruses, oil and grease, and heavy metals and other toxic substances. The primary source of many
of these pollutants is from the atmosphere (car and truck emissions), building surfaces and paving materials, and vehicles
(Schueler, 1987). Some of these pollutants, such as nutrients, heavy metals, and hydrocarbons, also travel attached to
sediments. Pollutants typically enter surface water through untreated stormwater runoff. The overall effect of development
results in a 10-fold increase in the amount of pollutants entering surface waters (after Schueler, 1987).

1.3.1 Sediment

Sediment is the most prevalent pollutant, by volume, polluting surface waters in the U.S. Virgin Islands. Uncontrolled
construction site sediment loads have been reported to average 35 to 45 tons/acre/year in the continental United States
(Novotny and Chesters, 1981). However, a 1986 study of erosion rates on St. Thomas and St. Croix estimated erosion
from a disturbed dirt road site to be 591 tons/acre/year (Wernicke, Seymour and Mangold, 1986). Studies of erosion
rates in the Fish Bay watershed on St. John have soil loss from dirt roads of between 100 to 600 tons per year
(MacDonald, et. al., 1997; Sampson, 1997).

Sediment has many short and long term harmful impacts on aquatic ecosystems. These include: increased turbidity,
reduced light penetration (which inhibits coral and seagrass growth), reduced prey capture for sight-feeding fish, clogging
of gills and filters in fish and shellfish, reduced spawning and juvenile fish survival, and decline of commercial and
recreational fishing success (Schueler, 1987). Heavy sediment deposition in coastal waters smothers seagrass beds and
coral reefs, increases sedimentation of channels and harbors (requiring more frequent dredging), changes bottom
composition, and leads to loss of use for recreational purposes (such as swimming and snorkeling) (U.S. EPA, 1993). The
primary cause of coral reef degradation in coastal areas is attributed to land disturbances and dredging activities due to
development activities (Rogers, 1990). Additional chronic effects may occur where there are sediments rich in clay or
organic matter (as is frequently the case in the Virgin Islands). Heavy metals and other toxic pollutants can tightly attach
to soil particles. When these contaminated sediments settle to the bottoms of ponds, bays, channels and lagoons, they
present a continued risk to aquatic and benthic life (organisms that live in the sediments at the bottom of bays, estuaries,
and other waterbodies), especially when the sediments are disturbed and resuspended (U.S. EPA, 1993).

1.3.2 Nutrients

Excess levels of nutrients (particularly nitrogen and phosphorus) that runoff to coastal waters cause an imbalance in the
natural nutrient cycle, leading to unwanted and excessive algae growth. This process is called eutrophication (Arms and
Camp, 1988; Dunne and Leopold, 1978; Miller, 1982). Excessive algae growth uses up dissolved oxygen in the water


Environmental Protection Handbook 1-5


Chapter 1


Introduction









and results in decreased fish, coral, and seagrass populations, and in extreme cases, can result in fish kills and widespread
destruction of benthic habitats. Algal blooms can also cause discoloration and odors, cover water surfaces depriving
aquatic organisms of light, and clog waterways. Surface algal scum and the release of toxins from sediment may also occur.

1.3.3 Bacteria, Viruses and Other Pathogens

Stormwater runoff from residential, commercial, and industrial areas usually contains levels of bacteria and other harmful
(pathogenic) organisms (viruses, parasites) that exceed public health standards for water-contact recreation or seafood
consumption. The presence of pathogens in runoff may result in beach closings for recreational uses due to public health
hazards, as well as contaminated fish and shellfish catches. In the Virgin Islands, beach closures frequently occur due to
sewage bypasses. However, as more stringent water quality monitoring is put in place, it is very likely that more beach
closures will occur due to contamination by bacteria, viruses and other pathogens.

1.3.4 Petroleum Hydrocarbons (Oil and Grease)

Most of the oil, grease and other petroleum hydrocarbon pollutants found in stormwater runoff come from car and truck
engines that leak oil and other fluids. Therefore, hydrocarbon levels are highest in stormwater runoff from parking lots,
roads, and gas stations. Some do-it-yourself auto mechanics also dump used oil directly on the ground, in guts, or into
storm drains. Petroleum-based hydrocarbon levels in surface waters are often high enough to kill aquatic organisms.

Oil and grease contain a wide variety of hydrocarbon compounds. Some of these are known to be toxic to aquatic life at
low concentrations, and many are human carcinogens. Hydrocarbons also tend to collect in bottom sediments where they
may persist for long periods of time and result in adverse impacts to benthic communities. Waterbodies with poor
circulation (such as enclosed marinas) are particularly susceptible to this phenomenon.

1.3.5 Heavy Metals and Toxic Substances

Heavy metals and other toxic materials found in stormwater runoff are of concern because of their poisonous effects on
aquatic life and their potential to contaminate ground water. Copper, lead, and zinc are the most common metals found
in stormwater runoff (many come from trucks and cars). A large amount of the metals present in stormwater runoff are
attached to sediment. Metals and toxic compounds that enter coastal waters can accumulate in the tissues of fish and
shellfish, harming human health.

1.4 PROPER PLANNING

Proper planning recognizes that land is a limited resource and has many physical variations that need to be considered
prior to development. Proper planning provides for the conservation and wise use of soil, water, plant and other natural
resources. Use of this publication, along with the Soil Survey of the Vjn Islands (USDA-NRCS, 1995; USDA-SCS, 1970,
http://www.statlab.iastate.edu/soils/soildiv/surveys/virgnis.pdf) to get information about the particular site, including soils
and erosion and sediment control information, is one of the first steps to proper planning.

1.4.1 Land is a Limited Resource

Primary consideration must be given to critical habitats and environmentally-sensitive areas (coastal areas and wetlands
such as guts, salt ponds, and mangrove lagoons) when planning for development. Available farmland must also be
considered in the process. Developments that result in irreversible land use changes represent a loss of valuable resources.
The long-term impacts of land conversion on the quality of the Virgin Islands' remaining natural ecosystems and coastal
water resources, as well as to the productive capacity of our farmland, should be evaluated.


1-6 Environmental Protection Handbook


Chapter 1


Introduction







Introduction


Most of the land in the Virgin Islands (St. John, St. Thomas and the North Shore of St. Croix) is steep and very
susceptible to soil erosion and sediment loss. Since constant development pressures are making this resource more and
more valuable, it becomes increasingly evident that future developmental pressure is going to be on steeper, more
erodible soils. Therefore, careful assessment of the land as a natural resource base is a necessary first step toward planning
the future development of an area. Development must be carefully adjusted to thatbase if serious environmental problems
are to be avoided.

1.4.2 Know Your Soil

One of the first steps in sound development planning is to know the soils and select the best possible site for the use
intended. Soil properties have a strong influence on the way that people use and should use the land. With the limited
flat land in the Virgin Islands, and much of that subject to flooding, development will increase on the steeper upland
areas. Soil properties of each parcel need to be determined prior to development to prevent costly mistakes.

The use of the Soil Survey of the VI,! i, Islands is a necessity in planning for development. The Soil Survey is a basic inventory
of the soil resources of the islands. The survey includes soil maps, soil descriptions, and soil interpretations. It can be used
as a tool in determining soil limitations for many suburban and urban uses and in selecting sites and designing structures
to minimize environmental and soil-related problems. Digital copies of the text of the Soil Survey of the iji,, Islands revised
in 1995 can be found and downloaded from: http://www.statlab.iastate.edu/soils/soildiv/surveys/virgnis.pdf. Maps can
be obtained digitally from the UVI Conservation Data Center, or the USDA-NRCS Caribbean Office in Puerto Rico.

1.5 ORGANIZATION OF THIS HANDBOOK

Chapter 2 discusses planning strategies and practices that can be used during development planning phases. Before
development occurs, land in a watershed is available for a number of pollution prevention options, such as setbacks,
buffers, or open space requirements. Siting requirements or restrictions and other land use ordinances, which are highly
effective in reducing pollution, are also more easily implemented during this period. If development has started before
these practices can be implemented, then these options may not be practicable or cost-effective.

Chapter 3 presents practices to control construction-related erosion and soil loss (sedimentation). The implementation
of proper erosion and sediment control practices during construction can significantly reduce erosion of valuable topsoil
and damage associated with sedimentation.

Chapter 4 presents practices to control stormwater runoff from new and existing development. Practices such as
detention ponds or constructed wetlands that treat stormwater runoff are most easily implemented in new projects where
their design can be incorporated into the overall development plan. After development has occurred, the lack of available
land severely limits the implementation of cost-effective treatment options. This chapter also presents information on
improving pollution prevention through controls that reduce stormwater runoff and pollution generated from ongoing
residential and commercial activities.

Chapter 5 provides information and examples for estimating soil erosion from proposed construction activities using the
Revised Universal Soil Loss Equation (RUSLE) developed by the USDA Natural Resources Conservation Service (USDA-
NRCS Caribbean Area, 1995).

Chapter 6 provides information on use of TR55, a computer model that uses the USDA-SCS Curve Number method
to predict stormwater runoff from development sites.


Environmental Protection Handbook 1-7


Chapter 1







Introduction


The Handbook also includes a number of appendices. Appendix A provides a Glossary of terms used in this handbook.
Appendices B and C provide design and construction specifications for erosion and sediment control practices and
stormwater practices, respectively, that are presented in the Handbook. Appendix D contains existing Territorial
legislation for the control of erosion, sedimentation, and stormwater runoff from development. This legislation is
modified, as necessary, to meet the requirements of any new Federal Programs. Finally, Appendix E is a list of References
used to develop this Handbook.

1.6 PURPOSE OF THIS HANDBOOK

The prevention and control ofnonpoint pollution from construction activities and other sources in coastal areas require
comprehensive solutions to protect and enhance coastal water quality. This handbook will supersede the Virgin Islands
Environmental Protection Handbook printed in 1976 (VICD, 1996) and updates the 1995 Revised Handbook (Wright,
1995). You will find many new practices in this handbook that reflect the growing body of knowledge regarding
stormwater, runoff and sedimentation control. Many studies conducted following the development of the 1976
Handbook have refined the information available regarding the impacts of nonpoint pollutants from construction sites
and other developing areas and the effectiveness and limitations of control practices. The U.S. Environmental Protection
Agency has also promulgated new rules, regulations and guidance governing stormwater discharges from construction and
urban areas, including the NPDES (National Pollution Discharge Elimination System) Stormwater Rules of 1990 and
the 1993 Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters that may apply
under certain conditions. This handbook was developed using the most current information available regarding practices
to control or prevent nonpoint pollution from urbanizing areas.

The Environmental Protection Handbook is intended for use only as a guide to the reader, indicating what practices,
standards, and procedures should be utilized in the development planning process in order to comply with the Virgin
Islands Environmental Protection Legislation, Title 12, Chapter 13 of the Virgin Islands Code and the corresponding
Virgin Islands Rules and Regulations. It is designed to assist contractors, developers, architects, engineers, draftsmen and
home builders implement a Stormwater, Erosion and Sediment Control Plan specifically designed for their construction
site.

The handbook provides useful information on stormwater, erosion, and sediment control practices that can be used to
prevent or reduce the discharge of sediment and other pollutants in stormwater runoff from your construction site. It
also describes the practices and controls, and details how, when and where these practices are applicable. However,
careful consideration must be given to selecting the most appropriate control measures based on site-specific conditions,
and on properly installing the controls in a timely manner.

The drawings presented in this Handbook are samples derived from publications developed by Federal, state and local
agencies regulating erosion and sediment control. These drawings are used for example purposes only, they are not
intended to be extracted for Erosion and Sediment Control Plans without prior review by a licensed engineer and/or
architect before construction.

1.7 REFERENCES

Arms, K. and P.S. Camp. 1988. Biology: A Journey Into Life, W.B. Saunders Company, New York, New York.

Arnold, C and J. Gibbons. 1998. Impacts of Development on Waterways, NEMO Project Factsheet 3, Sea Grant Marine
Advisory Program, University of Connecticut Cooperative Extension Service, Hamden, Connecticut.


1-8 Environmental Protection Handbook


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Introduction


The Handbook also includes a number of appendices. Appendix A provides a Glossary of terms used in this handbook.
Appendices B and C provide design and construction specifications for erosion and sediment control practices and
stormwater practices, respectively, that are presented in the Handbook. Appendix D contains existing Territorial
legislation for the control of erosion, sedimentation, and stormwater runoff from development. This legislation is
modified, as necessary, to meet the requirements of any new Federal Programs. Finally, Appendix E is a list of References
used to develop this Handbook.

1.6 PURPOSE OF THIS HANDBOOK

The prevention and control ofnonpoint pollution from construction activities and other sources in coastal areas require
comprehensive solutions to protect and enhance coastal water quality. This handbook will supersede the Virgin Islands
Environmental Protection Handbook printed in 1976 (VICD, 1996) and updates the 1995 Revised Handbook (Wright,
1995). You will find many new practices in this handbook that reflect the growing body of knowledge regarding
stormwater, runoff and sedimentation control. Many studies conducted following the development of the 1976
Handbook have refined the information available regarding the impacts of nonpoint pollutants from construction sites
and other developing areas and the effectiveness and limitations of control practices. The U.S. Environmental Protection
Agency has also promulgated new rules, regulations and guidance governing stormwater discharges from construction and
urban areas, including the NPDES (National Pollution Discharge Elimination System) Stormwater Rules of 1990 and
the 1993 Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters that may apply
under certain conditions. This handbook was developed using the most current information available regarding practices
to control or prevent nonpoint pollution from urbanizing areas.

The Environmental Protection Handbook is intended for use only as a guide to the reader, indicating what practices,
standards, and procedures should be utilized in the development planning process in order to comply with the Virgin
Islands Environmental Protection Legislation, Title 12, Chapter 13 of the Virgin Islands Code and the corresponding
Virgin Islands Rules and Regulations. It is designed to assist contractors, developers, architects, engineers, draftsmen and
home builders implement a Stormwater, Erosion and Sediment Control Plan specifically designed for their construction
site.

The handbook provides useful information on stormwater, erosion, and sediment control practices that can be used to
prevent or reduce the discharge of sediment and other pollutants in stormwater runoff from your construction site. It
also describes the practices and controls, and details how, when and where these practices are applicable. However,
careful consideration must be given to selecting the most appropriate control measures based on site-specific conditions,
and on properly installing the controls in a timely manner.

The drawings presented in this Handbook are samples derived from publications developed by Federal, state and local
agencies regulating erosion and sediment control. These drawings are used for example purposes only, they are not
intended to be extracted for Erosion and Sediment Control Plans without prior review by a licensed engineer and/or
architect before construction.

1.7 REFERENCES

Arms, K. and P.S. Camp. 1988. Biology: A Journey Into Life, W.B. Saunders Company, New York, New York.

Arnold, C and J. Gibbons. 1998. Impacts of Development on Waterways, NEMO Project Factsheet 3, Sea Grant Marine
Advisory Program, University of Connecticut Cooperative Extension Service, Hamden, Connecticut.


1-8 Environmental Protection Handbook


Chapter 1









Donahue, R.L., R.W. Miller, and J.C. Shickluna. 1983. Soils: An Introduction to Soils and Plant Growth, Fifth Edition, Prentice-
Hall, Inc., Englewood Cliffs, New Jersey.

Dunne, T. and L.B. Leopold. 1978. Water in Environmental P-I. mj,. W.H. Freeman and Company, New York, New York.

MacDonald, L.H., D.M. Anderson and W.E. Dietrich. 1997. 'ii .! Threatened: Land Use and Erosion on St. John,
U.S. Virgin Islands," Environmental Management, Vol. 21, No. 6, pp. 851-863.

Miller, G.T. 1982. Living in the Environment, Third Edition, Wadsworth Publishing Company, Belmont, California.

Novotny, V. and G. Chesters. 1981. II.,1'...'l..- ofNonpoint t..ll i.. Sources and Management, Van Nostrand Reinhold, New
York, New York.

Rogers, C.S. 1990. "Responses of Coral Reefs and Reef Organisms to Sedimentation," Marine Ecology Progress Series,
62:185-202.

Sampson, R. 1997. Precipitation, Runoff and Sediment Yield on St. John A Review of the Data, 319 Project Report to Island
Resources Foundation, February, 1997, St. Thomas, U.S. Virgin Islands.

Schueler, T.R. 1987. (.C.. .iil-.ij Urban Runoff A Practical Manual for Tl.iiiU and Designing Urban BMPs, Metropolitan
Washington Council of Governments, Department of Environmental Programs, Washington, DC. Publication Number
87703.

USDA-NRCS Caribbean Area. 1995. Revised Universal Soil Loss Equation (RUSLE) Caribbean Area, USDA Natural Resources
Conservation Service Field Office Technical Guide Section 1, San Juan, Puerto Rico.

USDA-NRCS. 1995. Soil Survey Vijn, Islands of the United States, U.S. Department of Agriculture Natural Resources
Conservation Service, U.S. Government Printing Office, Washington, DC.

USDA-SCS. 1970. Soil Survey Viji, Islands of the United States, U.S. Department of Agriculture Soil Conservation Service,
U.S. Government Printing Office, Washington, DC.

U.S. EPA. 1993. Guidance for I. ,; i;i,. Management Measures for Sources of Nonpoint t'..11'i ... in Coastal Waters, U.S.
Environmental Protection Agency, Office of Oceans, Wetlands and Watersheds, Washington, DC. Document Number
840-B-92-002.

Virgin Islands Conservation District. 1976. V1 1j, Islands EnvironmentalPr ., w1..i il. I..-... I-, Kingshill, St. Croix, U.S. Virgin
Islands.

Virgin Islands Department of Conservation and Cultural Affairs (DCCA). 1979. Environmental Laws and Regulations of the
Vliaj Islands, Title 12, Chapter 3, Trees and Vegetation Adjacent to Watercourses, 123 Cutting or Injuring Certain Trees, Equity
Publishing Corporation, Oxford, New Hampshire.

Wernicke, W., A. Seymour and R. Mangold. 1986. Sediment Study in the St. Thomas, St. Croix Areas of the United States V!,j,,
Islands, Donald E. Hamlin Consulting Engineers, Prepared for the V.I. Department of Conservation and Cultural Affairs.

Wright, J.A. 1995. 1995 VI1j'i Islands EnvironmentalPr -,i.,. i, ii. iwl.,!'-,l..1-, Virgin Islands Nonpoint Source Pollution Control
Committee, Virgin Islands Department of Planning and Natural Resources, St. Croix, U.S. Virgin Islands.


Environmental Protection Handbook 1-9


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Introduction


1-10 Environmental Protection Handbook


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CHAPTER 2: PLANNING PRACTICES
TABLE OF CONTENTS



2.1 PLANNING THE BASIS OF SMART DEVELOPMENT .............................. 2-1

2.2 KNOW YOUR SOILS ....................................................... 2-1

2.3 W ATERSHED PLANNING .................................................... 2-2

2.4 SITE PLANNING PRACTICES ................................................ 2-3

2.5 DEVELOPMENT PLANNING PRACTICES ..................................... .2-6

2.5.1 Pollution Prevention Management Plan .................................... 2-6

2.6 GOOD HOUSEKEEPING PRACTICES ......................................... 2-9

2.6.1 W aste D isposal ...................................................... 2-9

2.6.1.a Construction W astes ............................................ 2-9
2.6.1.b H hazardous Products ........................................... 2-10

2.6.2 M material M anagem ent ................................................ 2-10

2.6.2.a Pesticides ................................................... 2-11
2.6.2.b Petroleum Products ........................................... 2-11
2.6.2.c Fertilizers/D etergents ........................................ .. 2-12

2.6.3 Spills ...................................... ....................... 2-12

2.7 CO N CLU SIO N ............................................................ 2-13

2.8 REFEREN CES ............................................................. 2-13


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CatI 2 n iw rcie


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CHAPTER 2: PLANNING PRACTICES


2.1 PLANNING THE BASIS OF SMART DEVELOPMENT

Avoiding the adverse effects of development requires comprehensive planning. Studies by the USGS National Water
Quality Assessment (NAWQA) program in the last decade have shown that the water quality and aquatic health of any
given area reflect a complex combination of land and chemical use, land management practices, population density,
watershed development and natural features such as soils, geology, hydrology and climate. Contaminant concentrations
vary from rainy to dry season and watershed to watershed even among seemingly similar land uses and pollution sources,
different areas can have very different degrees of vulnerability (Southeast Watershed Forum, 2001).

Better site design reduces impervious cover, conserves natural areas and prevents stormwater pollution. Fitting the new
home or development into the natural topography and existing landscape is an important part of the overall planning
process. By following natural contours and features you can minimize clearing, reduce pollution potential, and provide
more open space to enhance property values and aesthetics. In addition to structural and non-structural best management
practices (BMPs), planning elements also include growth management, land use planning, long-term operation and
maintenance, and public education (CH2MHill, 1998). This chapter presents planning strategies and practices that can
be used during the initial phases of development to reduce nonpoint source pollution while enhancing land values.

2.2 KNOW YOUR SOILS

The first step to minimize problems involving land use and development is to know the soils and select the best possible
site for the intended use. Soil properties have a strong effect on the way that people use and should use the land. With
the limited flat land in the Virgin Islands (much of that subject to flooding), development will increase on steeper upland
areas. Soil properties of this land need to be determined prior to development to prevent costly mistakes.

The Soil Survey of the V1,ji, Islands (USDA-NRCS, 1995) provides vital information necessary to plan development. It is
a basic inventory of the soil resources of the islands. The survey includes soil maps, soil descriptions, and soil
interpretations. Soil maps depict soil boundaries and other features, such as guts and roads. The Soil Survey describes
the characteristics and properties of each kind of soil in the Virgin Islands, including soil texture (sand, silt or clay), slope,
depth, erodibility, permeability, degree of wetness, and other information useful to land developers. It can be used as a
tool in determining soil limitations for many rural and suburban uses and in selecting sites and designing structures to
minimize soil related problems.

Soils are rated according to their limitations for a given use. These limitations are described as either slight, moderate,
or severe. Soils with slight limitations have few problems that limit their use for a given purpose. Moderate limitations
can be overcome with careful planning and design of structures. Severe limitations indicate the need for very careful
consideration of a site prior to development. In some instances, the cost of overcoming a limitation may be excessive.

Some of the common soil-related limitations in the Virgin Islands are flooding, high shrink-swell potential, high
erodibility, very steep slopes, shallow or stony soils, and excessively dry climate. Examples of problems resulting from
these limitations include collapsing roadbeds, flooded buildings, cracking and failing building foundations, malfunctioning
septic systems, excessive erosion, and sedimentation damage. Measures necessary to help overcome these problems are
much easier to identify in the planning phase by using the Soil Survey. The Soil Survey can also be used to map sensitive
areas, such as steep slopes and highly erodible soils, wetlands, and gut corridors. Further information on the soils of the
Virgin Islands can be obtained from the USDA Natural Resources Conservation Service, the UVI Cooperative Extension
Service, or the V.I. Department of Agriculture.


Environmental Protection Handbook 2-1


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CHAPTER 2: PLANNING PRACTICES


2.1 PLANNING THE BASIS OF SMART DEVELOPMENT

Avoiding the adverse effects of development requires comprehensive planning. Studies by the USGS National Water
Quality Assessment (NAWQA) program in the last decade have shown that the water quality and aquatic health of any
given area reflect a complex combination of land and chemical use, land management practices, population density,
watershed development and natural features such as soils, geology, hydrology and climate. Contaminant concentrations
vary from rainy to dry season and watershed to watershed even among seemingly similar land uses and pollution sources,
different areas can have very different degrees of vulnerability (Southeast Watershed Forum, 2001).

Better site design reduces impervious cover, conserves natural areas and prevents stormwater pollution. Fitting the new
home or development into the natural topography and existing landscape is an important part of the overall planning
process. By following natural contours and features you can minimize clearing, reduce pollution potential, and provide
more open space to enhance property values and aesthetics. In addition to structural and non-structural best management
practices (BMPs), planning elements also include growth management, land use planning, long-term operation and
maintenance, and public education (CH2MHill, 1998). This chapter presents planning strategies and practices that can
be used during the initial phases of development to reduce nonpoint source pollution while enhancing land values.

2.2 KNOW YOUR SOILS

The first step to minimize problems involving land use and development is to know the soils and select the best possible
site for the intended use. Soil properties have a strong effect on the way that people use and should use the land. With
the limited flat land in the Virgin Islands (much of that subject to flooding), development will increase on steeper upland
areas. Soil properties of this land need to be determined prior to development to prevent costly mistakes.

The Soil Survey of the V1,ji, Islands (USDA-NRCS, 1995) provides vital information necessary to plan development. It is
a basic inventory of the soil resources of the islands. The survey includes soil maps, soil descriptions, and soil
interpretations. Soil maps depict soil boundaries and other features, such as guts and roads. The Soil Survey describes
the characteristics and properties of each kind of soil in the Virgin Islands, including soil texture (sand, silt or clay), slope,
depth, erodibility, permeability, degree of wetness, and other information useful to land developers. It can be used as a
tool in determining soil limitations for many rural and suburban uses and in selecting sites and designing structures to
minimize soil related problems.

Soils are rated according to their limitations for a given use. These limitations are described as either slight, moderate,
or severe. Soils with slight limitations have few problems that limit their use for a given purpose. Moderate limitations
can be overcome with careful planning and design of structures. Severe limitations indicate the need for very careful
consideration of a site prior to development. In some instances, the cost of overcoming a limitation may be excessive.

Some of the common soil-related limitations in the Virgin Islands are flooding, high shrink-swell potential, high
erodibility, very steep slopes, shallow or stony soils, and excessively dry climate. Examples of problems resulting from
these limitations include collapsing roadbeds, flooded buildings, cracking and failing building foundations, malfunctioning
septic systems, excessive erosion, and sedimentation damage. Measures necessary to help overcome these problems are
much easier to identify in the planning phase by using the Soil Survey. The Soil Survey can also be used to map sensitive
areas, such as steep slopes and highly erodible soils, wetlands, and gut corridors. Further information on the soils of the
Virgin Islands can be obtained from the USDA Natural Resources Conservation Service, the UVI Cooperative Extension
Service, or the V.I. Department of Agriculture.


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2.3 WATE2RSHEnD PLANNING
2.3 WATERSHED PLANNING The Basics of Watershed-Smart Development

A watershed is the area of land that drains water, soil, and 1. Design residential streets for the minimum required
pavement width needed to support travel lanes; on-street
pollutants to a common outlet along the coastline (bay, lagoon parking; and emergency, maintenance and service vehicle
or other coastal area). Watersheds are of different sizes and can 2. access (widths should be based on traffic olume)
2. Reduce the total length of residential streets by examining
be subdivided to the smallest area with an outlet. Large alternative street layouts to determine the best option for
watersheds, like Coral Bay or Benner Bay, have many outlets increasing the number of homes per unit length.
watersheds, like Coral Bay or Benner Bay, have many outlets 3. Reduce overall lot imperviousness by promoting alternative
into common nearshore areas. Since all land within a watershed driveway surfaces and shared driveways that connect two or
drains to a common outlet, any activity on that land will affect more homes togeth, naturally vegetated buffer system
4. Create a variable-width, naturally vegetated buffer system
downstream areas of the watershed and the bays or coastal areas along all guts that includes critical features like floodplains,
e w d d s P f in steep slopes, and wetlands.
the watershed drains into. Pollutants found in stormwater 5. Limit clearing and grading of forests and native vegetation
runoff can be easily carried from the land into a watershed's to the minimum amount needed to build lots, allow access
and provide fire protection. Manage a fixed portion of any
guts and drainage ways, eventually finding their way to salt community open space as protected green space.
ponds, and coastal and ground waters. 6. Encourage incentives such as density compensation, buffer
averaging property tax reduction, stormwatercredits, and by-
right open space development to promote conservation of
Pollution due to stormwater runoff (a nonpoint source) from gut buffers, forests, grass-lands, and other valuable areas.
7. Do not discharge unmanaged stormwater from new
urbanizing watersheds differs from point source pollution stormwater outfalls into jurisdictional wetlands, sole-source
(discharge of pollutants from a single outlet such as a sewer aquifers or other water bodies.
pipe or a wastewater pipe) in many ways: (From Southeast Watershed Forum, 2001)

Nonpoint sources generally cannot be monitored at their point of origin because their exact source is difficult
or impossible to trace.
Nonpoint source pollution is cumulative: it results from many actions by many different people, animals and/or
businesses, and is often spread over wide areas.
The extent of nonpoint source pollution may vary from place to place and from year to year, depending on
geography, geology, weather and human activities.
Nonpoint source pollution control requires more than structural solutions. Effective control requires the use of
comprehensive planning and best management practices, combined with public education, economic incentives,
and, in some cases, regulations.

Comprehensive planning is an effective nonstructural tool that can control nonpoint source pollution from urbanizing
areas. Poorly planned growth and development have the potential to degrade and destroy entire watersheds and coastal
ecosystems (Mantel et al., 1990). Where possible, growth should be directed to areas where it can be sustained with a
minimal impact on the natural environment. While stormwater runoff treatment practices (those that remove or reduce
pollutants in stormwater) are an important method of reducing water pollution, a combination of pollution prevention
and treatment practices is most effective. Planning, design, and education practices in combination with treatment
practices are generally more effective, require less maintenance, and are more cost-effective in the long-term than
treatment practices alone (U.S. EPA, 1993).

The primary opportunities to control pollutants in stormwater runoff occur during the siting and design phase; the
construction phase; and the post-construction phase. Before construction occurs, a number of pollution prevention
options, such as setbacks, buffers, or open space requirements, are available to the property owner. Siting requirements,
restrictions and other land use ordinances, such as zoning, are also more easily implemented during this period. These
practices protect environmentally sensitive areas such as wetlands and vegetative buffers that filter and trap sediments,
nutrients, and chemical pollutants. After construction has occurred, these options may no longer be practicable or cost-
effective. Table 2.1 describes the general steps to take in developing a watershed management plan.


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Chpe lni Pracie


Table 2.1. Watershed Management: A Step-by Step Guide (Livingston and McCarron, 1992).


1. Delineate and map watershed boundary and sub-basins
within the watershed.

2. Inventory and map natural stormwater conveyances and
storage systems.
(Guts, ponds, salt ponds, etc.)

3. Inventory and map existing man-made stormwater
conveyances and storage systems.
This includes all ditches, swales, storm sewers, detention
ponds, and retention areas and includes information such as
size, storage capacity and age.

4. Inventory and map existing land uses by sub-basin.

5. Inventory and map detailed soils by sub-basin.

6. Establish a clear understanding of water resources in
the watershed.
Analyze water quality, sediment, and biological data.
Analyze subjective information on problems (such as citizen
complaints). Evaluate waterbody use impairment -
frequency, timing, seasonality of problem. Conduct water
quality assessment low flows, seasonality.

7. Inventory pollution sources in the watershed.
Point sources location, pollutants, loadings, flow,
capacity, etc. Nonpoint sources type, location, pollutants,
loadings, etc.
land use/loading rate analysis for stormwater;
sanitary survey for septic systems; and
dry flow monitoring to locate illicit discharges.

8. Identify and map future land uses by sub-basin.
Conduct land use loading rate analyses to assess potential
effects of various land use scenarios.


9. Identify planned infrastructure improvements 5-year,
20-year.
Stormwater management deficiencies should be
coordinated and scheduled with other infrastructure
development projects.

10. Analysis.
Determine infrastructure and natural resources management
needs within each watershed.

11. Set resource management goals and objectives.
Before corrective actions can be taken, a resource
management target must be set. The target can be defined
in terms of water quality standards; attainment and
preservation of beneficial uses; or other resource
management objectives.

12. Determine pollutant reduction (for existing and future
land uses) needed to achieve water quality goals.

13. Select appropriate management practices (point source,
nonpoint source) that can be used to achieve the goal.
Evaluate pollutant removal effectiveness, land owner
acceptance, financial incentives and costs, availability of
land, operation and maintenance needs, feasibility, and
availability of technical assistance.

14. Develop watershed management plan.
Develop watershed management plan specific to the area,
including such elements as:
existing and future land use plan;
master stormwater management plan that addresses
existing and future needs;
wastewater management plan including septic system
maintenance programs; and
infrastructure and capital improvements plan.


The Center for Watershed Development has developed a manual of better site design principles (CWP, 1998) for
the national Site Planning Roundtable that proscribes innovative and effective resource management techniques to protect
waterways, estuaries and coastal habitats. The principles revolve around the theory that the suburban landscape consists
of three habitats: the car habitat (roads, driveways, and parking lots), the human habitat (where we live and work,
including our homes and yards), and open spaces and natural areas that are relatively undeveloped (CWP, 1998). Table
2.2 describes the 22 site design principles by habitat category.


2.4 SITE PLANNING PRACTICES


Site planning practices apply to individual sites rather than watersheds or regional drainage basins. The goal of site
planning is to reduce pollution generation and to minimize the impacts of stormwater runoff and associated pollutants.
The basic premise is that effective site layouts and designs can reduce the need for conventional structural BMPs, reducing
development costs (CH2MHill, 1998). Tables 2.3-2.6 (pages 2.7 2.9) contain checklists developed by EPA for use in
designing stormwater pollution prevention plans for construction sites greater than 1 acre, pursuant to EPA stormwater
regulations. These checklists can be used by Virgin Islands developers and contractors to design pollution prevention
plans.


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Table 2.2. Model development principles for better site design (CWP, 1998).

Residential Streets and Parking Lots
1. Design residential streets for the minimum required pavement width needed to support travel lands; on-street parking; and emergency,
maintenance, and service vehicle access. These widths should be based on traffic volume.
2. Reduce the total length of residential streets by examining alternative street layoutsto determine the best option for increasing the number
of homes per unit length.
3. Wherever possible, residential street right-of-way widths should reflect the minimum required to accommodate the travel-way, the
sidewalk, and vegetated open channels swaless).
4. Minimize the number of residential street cul-de-sacs and incorporate landscaped areas to reduce their impervious cover. The radius of
cul-de-sacs should be the minimum required to accommodate emergency and maintenance vehicles. Alternative turnarounds should be
considered.
5. Where density, topography, soils, and slope permit, vegetated open channels should be used in the street right-of-way to convey and treat
stormwater runoff.
6. The required parking ratio governing a particular land use or activity should be enforced as both a maximum and a minimum in order to
curb excess parking space construction. Existing parking ratios should be reviewed for conformance taking into account local and national
experience to see if lower ratios are warranted and feasible.
7. Parking codes should be revised to lower parking requirements where mass transit is available or enforceable shared parking
arrangements are made.
8. Reduce the overall imperviousness associated with parking lots by providing compact car spaces, minimizing stall dimensions,
incorporating efficient parking lanes, and using pervious materials in spillover parking areas.
9. Provide meaningful incentives to encourage structured and shared parking to make it more economically viable.
10. Wherever possible, provide stormwater treatment for parking lot runoff using bioretention areas, filter/buffer strips, and/or other practices
that can be integrated into required landscaping areas and traffic islands.
Lot Development
11. Advocate open space development that incorporates smaller lot sizes to minimize total impervious area, reduce total construction costs,
conserve natural areas, provide community recreational space, and promote watershed protection.
12. Relax side yard setbacks and allow narrower frontagesto reduce total road length in the community and overall site imperviousness. Relax
front setback requirements to minimize driveway lengths and reduce overall lot imperviousness.
13. Promote more flexible design standards for residential subdivision sidewalks. Where practical, consider locating sidewalks on only one
side of the street and providing common walkways linking pedestrian areas.
14. Reduce overall lot imperviousness by promoting alternative driveway surfaces and shared driveways that connect two or more homes
together.
15. Clearly specify how community open space will be managed and designate a sustainable legal entity responsible for managing both
natural and recreational open space.
16. Direct rooftop runoff (any not captured by cisterns) to pervious areas such as yards, open channels, or vegetated areas and avoid routing
rooftop runoff to the roadway and the stormwater conveyance system.
Conservation of Natural Areas
17. Create a variable width, naturally vegetated buffer system along all guts that also encompasses critical environmental features such as
the 100-year floodplain, steep slopes and wetlands.
18. The riparian buffer (around guts) should be preserved or restored with native vegetation that can be maintained throughout the delineation,
plan review, construction, and occupancy stages of development.
19. Clearing and grading of forests and native vegetation at a site should be limited to the minimum amount needed to built lots, allow access,
and provide fire protection. A fixed portion of any community open space should be managed as protected green space in a consolidated
manner.
20. Conserve trees and other vegetation at each site by planting additional vegetation, clustering tree areas, and promoting the use of native
plants. Wherever practical, manage community open spaces, street rights-of-way, parking lot islands, and other landscaped areas to
promote natural vegetation.
21. Incentives and flexibility in the form of density compensation, buffer averaging, property tax reduction, stormwater credits, and by-right
open space development should be encouraged to promote conservation of stream/gut buffers, forests, grass lands, and other areas of
environmental value. In addition, off-site mitigation consistent with locally adopted watershed plans should be encouraged.
22. New stormwater outfalls should not discharge unmanaged stormwater into jurisdictional wetlands, sole-source aquifers, or sensitive areas.


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Objectives of site planning practices


The following objectives should be incorporated into the site development process:

Disturb the smallest area necessary for current construction activities in order to reduce erosion and soil loss;
Avoid disturbing unstable soils or soils especially susceptible to erosion and soil loss, and favor sites where
development will minimize erosion and soil loss;
Protect and retain native plants as much as possible in order to decrease stormwater runoff, filter and/or absorb
pollutants, and maintain site hydrology;
Minimize the percentage of impervious area on the site;
Avoid alteration, modification or destruction of guts and other natural drainage features on the site (V.I. Code
(V.I. DCCA, 1979) requires a permit to cut any tree within 25 feet of the edge of a gut);
Design sites to preserve natural buffers adjacent to guts, salt ponds and coastal waters; and
Minimize water quality impacts from landscaping activities by applying chemicals properly (see Good
Housekeeping Practices, section 2.6).

Site planning and evaluation are extremely important they can significantly reduce sediment control
practice costs by minimizing erosion and keeping sediment on the construction site. Long-term
maintenance efforts and costs can also be significantly reduced. While designing the site, planners should
identify sensitive areas and land forms that can provide water quality protection, target these areas for preservation or
conservation, and incorporate them into the site design. Highly erodible soils should not be disturbed. By locating
development away from highly erodible soils, erosion and sedimentation can be significantly reduced. Sediment loads
from developing areas where new construction is occurring can be 5 to 500 times greater than loads from undeveloped
areas (Gray and Leiser, 1982). Because of the adverse effects of sedimentation (as described in Chapter 1) and the many
nonpoint source pollutants (including heavy metals and nutrients) that can be attached to sediment, it is important to
limit the volume of sediment entering coastal waters.


What are site planning practices that can be used to reduce runoff, erosion and sedimentation?


Phasing and Limiting Areas of Disturbance Erosion potential can be reduced by not clearing and grading
all post-development buffer zones, configuring the site plan to retain large areas of open space, and phasing
construction to limit the amount of disturbed area at any given time.
Low Disturbance/Low Maintenance This site development approach allows clearing and site grading only
within a carefully defined building area, preserving and protecting the surrounding natural vegetation. Landscape
designs should avoid exotic plants that need large amounts of water, fertilizers and pesticides. Rare, threatened,
and endangered species should be preserved. Retaining existing vegetation holds the soil in place and helps to
reduce runoff volume and rate, reducing erosion. Low disturbance/low maintenance strategies also minimize
fertilizers and pesticide applications that can pollute coastal waters and harm fish and reef habitats.
Cluster Development Concentrate development and construction activity on a limited area of a site, leaving
the remaining area undisturbed. Clustering promotes the design of more effective stormwater runoff, erosion
and sediment control practices, helps preserve environmentally sensitive areas, and reduces impervious area.
Site Fingerprinting Fingerprinting reduces the total amount of disturbed area within a site by placing
development away from environmentally sensitive areas (wetlands, guts, floodplains, steep slopes, etc.). At a
subdivision or lot level, ground disturbance is confined to areas where structures (buildings, septic system),
driveways and roads will exist after construction is complete.



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Setbacks and Buffers Setbacks provide an area between buildings, parking lots and roads and protected areas
such as salt ponds, guts, shorelines, or wetlands. A buffer strip is the transitional vegetated area closest to the
water body or wetland. Buffers are designed to minimize erosion, stabilize gut banks or shorelines, filter runoff
pollutants from adjacent developments, preserve fish and wildlife habitat, provide privacy screening and preserve
aesthetic value, and provide access for maintenance or trails (CH2MHill, 1998).
Preserving Natural Drainage Channels Natural drainage features (guts) should be preserved during
development because of their ability to absorb and reduce stormwater runoff flows and to filter pollutants. V.I.
Code (V.I. DCCA, 1979) requires a permit to cut any trees within 25 feet of the edge of a gut. Cluster
development can be used to preserve guts and allow for incorporation of these features into a site design.
Minimizing Impervious Areas Impervious areas prevent the infiltration of rainfall into the soil, leading to
increased volumes and rates of stormwater runoff. Some practices to minimize impervious areas include:
reducing street and sidewalk widths; reducing the use of storm sewers, using permeable materials for sidewalk
and driveway construction; requiring open spaces; and/or using porous or cellular pavement.
Encourage Xeriscaping Xeriscaping is a landscaping method that maximizes water conservation by using
drought-tolerant native species. Xeriscaping can reduce landscape maintenance by as much as 50% by reducing
watering requirements and fertilizer and pesticide applications (U.S. EPA, 1993). (Contact the USDA Natural
Resources Conservation Service or the UVI Cooperative Extension Service for more information on xeriscaping
with native plants.)
Development Designed to Fit Site Topography- Creating a design that avoids the need for major grading
changes will reduce project expense, soil compaction, destruction of natural drainage ways, and loss of site
diversity. By varying lot sizes and building styles and by using at least limited clustering, the need for mass grading
can be significantly reduced.

2.5 DEVELOPMENT PLANNING PRACTICES

Planning practices are used to avoid impacting areas that are particularly susceptible to erosion and soil loss; to preserve
areas that provide important water quality benefits and/or are necessary to maintain wetland or aquatic ecosystems; and
to locate development, including roads, highways, and bridges, to protect the natural integrity of water bodies and natural
drainage systems. All of these practices will minimize runoff, erosion and sedimentation.

2.5.1 Pollution Prevention Management Plan

The most effective way to minimize runoff, erosion and sedimentation before and after construction is to implement a
pollution prevention management plan. A pollution prevention management plan is a comprehensive approach that
addresses the needs of a site or watershed, including land use, stormwater, erosion and sediment control practices,
pollutant reduction strategies, and pollution prevention techniques. Before developing a pollution prevention management
plan you must first define site, sub-watershed and/or watershed boundaries, target sensitive areas, identify pollutants of
concern, and conduct a resource inventory and information analysis. Once environmentally-sensitive areas are identified,
areas essential to safeguard coastal waters and prevent nonpoint source pollution can be protected.


The components of a pollution prevention management plan


A pollution prevention management plan must have defined, measurable goals (for example, maintaining runoff volumes
at a calculated level relative to undeveloped conditions) in order to be effective. Design and implementation specifications
for runoff, erosion and sediment control practices are then incorporated into the plan as methods to achieve the goal.
This type of planning is especially necessary when designing larger developments requiring a major permit (i.e.,
developments greater than 1 acre).


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Pollution prevention management plan implementation



Once critical areas, land use designations and goals have been identified, defined and established, management plan
implementation strategies can be developed (i.e., once you have followed the steps in Table 2.1). The following are
examples of implementation tools that have been successful at controlling nonpoint source pollution:


Infrastructure planning;
Limits on impervious surfaces, encouragement of open space and cluster development;
Setbacks (buffer zones);
Slope restrictions;
Site plan reviews;
Mapping; and
Environmental impact assessment statements (U.S. EPA, 1993).

Table 2.3. EPA Baseline Construction General Permit Requirements: Pre-Construction Checklist (U.S. EPA, 1992).

STORMWATER POLLUTION PREVENTION PLANS

1. A site description, including:
O The nature of the activity
O Intended sequence of major construction activities
O The total area of the site
O The area of the site that is expected to undergo excavation
O The runoff coefficient of the site after construction is complete
O Existing soil or stormwater data
O A site map with:
0 Drainage patterns
O Approximate slopes after major grading
O Area of soil disturbance
O Outline of areas that won't be disturbed
O Location of major structural and non-structural controls
O Areas where stabilization practices are expected to occur
O Surface waters
O Stormwater discharge locations
O The name of the receiving waters)

2. A description of controls:
2.1 Erosion and sediment controls, including:
O Stabilization practices for all areas disturbed by construction
O Structural practices for all drainage/discharge locations
2.2 Stormwater management controls, including:
O Practices used to control pollutants occurring in stormwater discharges after construction activities are complete
O Velocity dissipation devices to provide non-erosive flow conditions from the discharge point along the length of any
outfall
2.3 Other controls including:
O Waste disposal practices that prevent discharge of solid materials to waters of the U.S.
O Practices to minimize offsite tracking of sediments by construction vehicles
O Practices to ensure compliance with Federal and Territorial waste disposal, sanitary sewer, and septic system
regulations
2.4 0 Description of the timing during construction when practices will be implemented

3. 0 Are Federal and Territorial requirements incorporated into the plans?

4. 0 Are Maintenance procedures for control measures identified in the plan?

5. 0 Identification of allowable non-stormwater discharges and pollution prevention practices

6. 0 Contractor certification

7. 0 Plan certification


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Table 2.4. Stormwater Pollution Prevention Plan: Construction/Implementation Checklist (U.S. EPA, 1992).

1. Maintain records of construction activities, including:
O Dates when major grading activities occur
O Dates when construction activities temporarily cease on a portion of the site
O Dates when construction activities permanently cease on a portion of the site
O Dates when stabilization measures are initiated on the site

2. Prepare inspection reports summarizing:
O Name of inspector
O Qualifications of inspector
O Practices/areas inspected
O Observed conditions
O Changes necessary to the Stormwater Pollution Prevention Plan

3. Report releases of reportable quantities of oil or hazardous materials (if they occur):
O Notify the National Response Center 1-800-424-8802 immediately
O Notify DPNR in writing within 14 days
O Modify the pollution prevention plan to include:
the date of release
circumstances leading to the release
steps taken to prevent re-occurrence of the release

4. Modify pollution prevention plan as necessary to:
O Comply with minimum permit requirements when notified by EPA that the plan does not comply
O Address a change in design, construction, operation or maintenance that has an effect on the potential for discharge of
pollutants
O Prevent re-occurrence of reportable quantity releases of a hazardous material or oil


Table 2.5. Pollution Prevention Plan for Stormwater Discharge Associated with Construction Activities: Erosion and Sediment Control Checklist
(U.S. EPA, 1992).

INSTRUCTIONS: THIS CHECKLIST LISTS THE MINIMUM SEDIMENT EROSION CONTROL REQUIREMENTS UNDER THE US EPA GENERAL PERMIT. CHECK
EACH ITEM AND FILL IN THE BLANKS BELOW TO EVALUATE COMPLIANCE FOR EACH DRAINAGE AREA AND LOCATION.

STABILIZATION PRACTICES

D Stabilization will be initiated on all disturbed areas where construction activity will not occur for a period of more than 21 calendar days
by the 14th day after construction activity has permanently or temporarily ceased.

Stabilization practices to be used include:


D Temporary Seeding
D Permanent Seeding


D Sod Stabilization
D Mulching


D Filter Fabrics
D Other


STRUCTURAL PRACTICES

D Flows from upstream areas will be diverted from exposed soils. Practices to be used include:

0 Drainage Swale 0 Diversion Dike/Swale 0 Other

Drainage areas less than 10 disturbed acres Drainage areas of 10 or more disturbed acres

D Sediment controls will be installed D A sediment basin will be installed

Sediment controls include: 0 A sediment basin is not attainable on the site; therefore, the
following sediment controls will be installed:
D Sediment Basin
D Sediment Trap D Sediment Trap
D Silt Fence or equivalent controls along all sideslope and D Silt Fence or equivalent controls along the sideslope and
downslope boundaries downslope boundaries

Sediment Basin Storage Calculation

acres area draining to the sediment basin
X
3,600 cubic feet of storage per acre*

cubic feet of storage required for the basin

*For further discussion of storage requirements, refer to Chapter 3 and Appendix B, Sediment Basins.

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Table 2.6. Stormwater Pollution Prevention Plan: Final Stabilization/Termination Checklist (U.S. EPA, 1992).
1. O All soil disturbing activities are complete

2. O Temporary erosion and sedimentation control Practices have been removed or will be removed at an
appropriate time

3. O All areas of the construction site not otherwise covered by a permanent pavement or a structure have been
stabilized with a uniform perennial vegetative cover with a density of at least 70%, or equivalent measures
have been employed


2.6 GOOD HOUSEKEEPING PRACTICES

Good housekeeping refers to keeping a clean and orderly construction site. Good housekeeping practices and common
sense prevent contamination of stormwater runoff from construction site chemicals. Good housekeeping practices can
reduce accidental spills, improve spill response times, and reduce safety hazards. These practices are inexpensive, relatively
easy to implement, and are often effective in preventing stormwater contamination. They can also reduce costs by
preventing unnecessary loss of products.


Different types of good housekeeping practices


There are three areas related to good housekeeping on a construction site that should be addressed in each watershed
or site development plan. These areas are: proper disposal of building material wastes; proper storage and handling of
chemicals used on the construction site; and implementation of a spill prevention and control plan.

2.6.1 Waste Disposal

Proper management and disposal of building materials and other construction site wastes is an important part of pollution
prevention. Sources of pollution include surplus or refuse building materials as well as hazardous wastes. All controls and
practices must meet the requirements of your Earth Change or CZM Permit and other Federal and Territorial
requirements your site is subject to.

This section discusses some of the waste materials encountered at construction sites and, in general, how they should be
stored and handled to minimize their exposure to stormwater. However, you should contact the Department of Public
Works (DPW) to find out more about waste disposal regulations, or the Department of Planning and Natural Resources
(DPNR) to find out how to safely handle, store and dispose of hazardous and toxic chemicals.

2.6.1.a Construction Wastes

Construction projects tend to generate large amounts of solid waste materials that are unique to this activity. These wastes
may include, but are not limited to:

Trees and shrubs removed during clearing and other phases of construction;
Packaging materials (wood, paper, plastic, cardboard, etc.);
Scrap or surplus building materials (scrap metals, rubber, plastic and glass pieces, masonry products, etc.);
Paints and paint thinners; and
Materials generated by structure demolition (rubble).


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Steps to be taken to properly dispose of construction wastes


Select a designated waste collection area onsite;
Provide an adequate number of containers with covers;
Locate containers in a covered area, when possible;
Arrange for waste collection before containers overflow;
Provide immediate clean-up in the event of a spill;
Plan for additional containers and more frequent pick-ups during demolition phases;
Make sure that construction waste is collected, removed and disposed of only at authorized disposal areas; and
Check with DPW or DPNR for specific guidance.

2.6.1. b Hazardous Products

Many materials found at construction sites may be hazardous either to personnel or to the environment. Always read the
labels of the materials and products present onsite--they may contain warning information that will help you be aware
of potential problems. Hazardous products at a construction site include, but are not limited to:

Paints;
Acids for cleaning masonry surfaces;
Cleaning solvents;
Chemical additives used for soil stabilization;
Concrete curing compounds and additives; and
Pesticides, herbicides, fungicides, and rodenticides.


Basic management practices that can minimize or prevent contamination of stormwater from
hazardous products on construction sites


Most problems involving hazardous materials result from carelessness or from not using common sense. The practices
listed below will help avoid problems associated with hazardous material disposal. Section 2.6.2 contains further
information on hazardous material handling and storage and section 2.6.3 discusses spill prevention plans.

Check with DPNR to determine the requirements for hazardous material disposal.
Use all of the product before properly disposing of the container if you must dispose of surplus products, do
not mix products together unless specifically recommended by the manufacturer.
Do not remove the original product label from the container, it contains important information.
Follow the manufacturer's recommended method of disposal for the product and the empty container (often
found on the label).

2.6.2 Material Management

Material management is important as the best way to avoid a problem is to prevent it at its source. On a construction site,
the material storage area can become a major source of pollution due to the mishandling of materials or accidental spills.
An inventory of the material storage area and of the site should be made. Special care should be taken to identify any
materials that have the potential to come into contact with stormwater.


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There are a number of risks (other than stormwater contamination) to consider in the management of materials on a
construction site, including health and safety of employees and groundwater contamination. However, this section only
addresses stormwater contamination risks. Contact DPNR for information about measures to minimize other risks.


Materials to be considered when evaluating potential risks


Pesticides;
Petroleum products;
Fertilizers and detergents (nutrient sources);
Construction chemicals;
Other pollutants; and
Hazardous products (see previous section).


Information to be evaluated for onsite risk assessment


What types of materials are stored onsite?
How long will the materials be stored before they are used?
Are you storing more than is needed?
How are the materials stored and distributed?
How can potential contact with stormwater be avoided?

2.6.2.a Pesticides

Pesticides include insecticides, rodenticides, and herbicides commonly used on construction sites.


How to reduce the risks of using pesticides


Handle the materials as infrequently as possible; and
Observe all applicable Federal and Territorial regulations when using, handling or disposing of these materials.


Management practices that can be used to reduce risks from pesticide use


Management practices that can reduce the amount of pesticides coming into contact with stormwater include the
following:

Store pesticides in a dry covered area;
Provide curbs, dikes or berms to contain potential pesticide spills;
Have measures on site to contain and clean up pesticide spills; and
Strictly follow recommended application rates and methods.

2.6.2. b Petroleum Products

Petroleum products include oil, gasoline, lubricants, and asphaltic substances such as paving materials. These materials
should be carefully handled to minimize their exposure to stormwater. Petroleum products usually occur in two areas:


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areas where road construction of some type is occurring and vehicle storage areas or areas of onsite fueling or equipment
maintenance.


Practices that can be used to reduce the risks of using petroleum products


Provide equipment to contain and clean up petroleum spills in fuel storage areas or on maintenance and fueling
vehicles;
Store petroleum products and fuel vehicles in covered areas;
Contain and clean up petroleum spills immediately;
Perform preventative maintenance of equipment used onsite to prevent leakage (e.g., check for and fix gas or
oil leaks in construction vehicles on a regular basis); and
Properly apply asphaltic substances (see manufacturer's instructions) to reduce spill risks;
Build impervious dikes or berms to contain any spills; and
Install oil/grease separators in stormwater inlets (see Chapter 4).

2.6.2. c Fertilizers/Detergents

The proper landscaping or revegetation of construction sites often requires using fertilizers and detergents that contain
nutrients such as nitrogen and phosphorus. Excess quantities of these nutrients can be washed away by stormwater runoff
and become a major pollution problem. Excess nutrients in wetlands and coastal waters can cause eutrophication and
other pollution problems.


Practices that can be used to reduce the risks of nutrient pollution


Only apply fertilizers when absolutely necessary to revegetate disturbed areas;
Apply fertilizers to a minimum area and at the minimum recommended amount and rate (time-released
fertilizers can be used);
Work fertilizers into the soil to reduce exposure of nutrients to stormwater runoff;
Seed and fertilize in one application (see section on Hydroseeding in Chapter 3); and
Implement good erosion and sediment control practices to help reduce the amount of sediment and fertilizers
that leave the site (see Chapter 3).

2.6.3 Spills

Spills of pesticides, petroleum products, or other toxic or hazardous products can contaminate soil, water and waste
materials resulting in potential health risks. Preparations should be made to deal quickly and effectively with accidental
spills. A spill control plan can help you be prepared. This section discusses your additional responsibilities if there is a
reportable quantity spill.


A spill control plan should include methods to:


Stop the source of the spill;
Contain the spill (i.e., utilizing impervious liners and collection containment systems);
Clean up the spill (i.e., filtration systems);
Dispose of all materials contaminated by the spill; and
Contact qualified personnel responsible for spill prevention and control.


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Specific spill prevention methods and responses that can be used


Store and handle materials to prevent spills.
Tightly seal containers.
Make sure all containers are clearly labeled.
Stack containers neatly and securely.
Reduce stormwater contact if there is a spill.
Have cleanup procedures clearly posted.
Have cleanup materials readily available.
Contain any liquid.
Stop the source of the spill.
Cover the spill with absorbent material such as kitty litter or sawdust.
Discard contaminated materials according to manufacturer's instructions or according to Federal or Territorial
requirements.
Identify personnel responsible for responding to a spill of toxic or hazardous materials.
Provide personnel spill response training.
Post names of spill response personnel.
Keep the spill area well ventilated.
If necessary, use a private firm that specializes in spill cleanup.

2.7 CONCLUSION

The importance of proper development planning and the use of good housekeeping practices cannot be overstated. It
is cheaper in the long run, for both the developer and the community, to effectively plan a development to minimize
pollution than to clean-up the effects of poor planning and management after the fact.

2.8 REFERENCES

Center for Watershed Protection (CWP). 1998. Better Site Design: A H. ,..'-....l for Changing Development Rules in Your
Community, Prepared for the Site Planning Roundtable by the Center for Watershed Protection, Ellicott City, Maryland,
www.cwp.org.

CH2MHill. 1998. Pennsylvania II.,W'-... of Best Management Practices for Developing Areas, Pennsylvania Association of
Conservation Districts, Inc., Harrisburg, Pennsylvania.

Gray, D.H. and A.T. Leiser. 1982. Biotechnical Slope Protection and Erosion Control, Van Nostrand Reinhold, New York, New
York.

Livingston, E.H. and E. McCarron. 1992. Stormwater Management: A Guide for Floridians, Florida Department of
Environmental Regulation, Tallahassee, Florida.

Mantell, M.A., S.F. Harper, and L. Propst. 1990. Creating Successful Communities: A Guidebook to Growth Management Strategies,
Island Press, Washington, DC.

Southeast Watershed Forum. 2001. Growing Smarter: Linking Land Use &Water Quality, Southeast Watershed Forum, Vol.4,
Issue 1, Spring/Summer 2001, Duluth, Georgia.



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Specific spill prevention methods and responses that can be used


Store and handle materials to prevent spills.
Tightly seal containers.
Make sure all containers are clearly labeled.
Stack containers neatly and securely.
Reduce stormwater contact if there is a spill.
Have cleanup procedures clearly posted.
Have cleanup materials readily available.
Contain any liquid.
Stop the source of the spill.
Cover the spill with absorbent material such as kitty litter or sawdust.
Discard contaminated materials according to manufacturer's instructions or according to Federal or Territorial
requirements.
Identify personnel responsible for responding to a spill of toxic or hazardous materials.
Provide personnel spill response training.
Post names of spill response personnel.
Keep the spill area well ventilated.
If necessary, use a private firm that specializes in spill cleanup.

2.7 CONCLUSION

The importance of proper development planning and the use of good housekeeping practices cannot be overstated. It
is cheaper in the long run, for both the developer and the community, to effectively plan a development to minimize
pollution than to clean-up the effects of poor planning and management after the fact.

2.8 REFERENCES

Center for Watershed Protection (CWP). 1998. Better Site Design: A H. ,..'-....l for Changing Development Rules in Your
Community, Prepared for the Site Planning Roundtable by the Center for Watershed Protection, Ellicott City, Maryland,
www.cwp.org.

CH2MHill. 1998. Pennsylvania II.,W'-... of Best Management Practices for Developing Areas, Pennsylvania Association of
Conservation Districts, Inc., Harrisburg, Pennsylvania.

Gray, D.H. and A.T. Leiser. 1982. Biotechnical Slope Protection and Erosion Control, Van Nostrand Reinhold, New York, New
York.

Livingston, E.H. and E. McCarron. 1992. Stormwater Management: A Guide for Floridians, Florida Department of
Environmental Regulation, Tallahassee, Florida.

Mantell, M.A., S.F. Harper, and L. Propst. 1990. Creating Successful Communities: A Guidebook to Growth Management Strategies,
Island Press, Washington, DC.

Southeast Watershed Forum. 2001. Growing Smarter: Linking Land Use &Water Quality, Southeast Watershed Forum, Vol.4,
Issue 1, Spring/Summer 2001, Duluth, Georgia.



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USDA-NRCS. 1995. Soil Survey Vijm, Islands of the United States, U.S. Department of Agriculture Soil Conservation Service,
U.S. Government Printing Office, Washington, DC.

U.S. EPA. 1993. Guidance \*., Environmental Protection Agency, Office of Wetlands, Oceans and Watersheds, Washington, DC. Document Number
840-B-92-002.

U.S. EPA. 1992. Stormwater Management for Construction Activities: Developing Pollution Prevention Plans and Best Management
Practices, U.S. Environmental Protection Agency, Office of Wetlands, Oceans and Watersheds, Washington, DC.
Document Number 832-R-92-005.

V.I. Department of Conservation and Cultural Affairs (DCCA). 1979. Environmental Laws and Regulations of the V,, j Islands,
Title 12, Chapter 3, Trees and Vegetation Adjacent to Watercourses, 123 Cutting or Injuring Certain Trees, Equity Publishing
Corporation, Oxford, New Hampshire.


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Chapter 3 Erosion and Sediment Control Practices

CHAPTER 3: EROSION AND SEDIMENTATION CONTROL PRACTICES
TABLE OF CONTENTS




3.1 INTRODUCTION ....................................................... 3-1

3.2 STABILIZATION PRACTICES .............................................. 3-2

Preservation and Protection of Natural Vegetation ............................ 3-3
Filter Strips ......................................................... 3-5
Land Grading ........................................................ 3-6
Surface Roughening ................................................... 3-7
Tem porary Seeding ................................................... 3-8
Permanent Seeding and Planting ......................................... 3-10
Mulches, Mats and Geotextiles .......................................... 3-11
Soil Binders/Tackifiers ................................................ 3-14
Soil Retaining Walls .................................................. 3-15
Soil Bioengineering .................................................. 3-16

3.3 STRUCTURAL PRACTICES .............................................. 3-19

Perimeter Dikes and Swales ............................................ 3-19
Drainage Swales ..................................................... 3-20
Temporary Storm Drain Diversion ....................................... 3-21
Silt Fence .......................................................... 3-22
Gravel/Stone Filter Berm .............................................. 3-24
Stabilized Construction Entrance ........................................ 3-24
Check Dams/Triangular Dikes/Berms ..................................... 3-25
Sediment Traps ..................................................... 3-27
Temporary Sediment Basin ...................................... ...... 3-30
Storm Drain Inlet Protection ........................................... 3-31
Outlet Protection .................................................... 3-33
Gabion Inflow Protection ............................................... 3-34

3.4 REFERENCES ......................................................... 3-35

















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CHAPTER 3: EROSION AND SEDIMENTATION CONTROL PRACTICES

3.1 INTRODUCTION

Erosion from construction sites, dirt roads and other disturbed lands are a source of sediment, toxic chemicals,
and excess nutrients that can pollute coastal waters. Runoff from construction sites is by far the largest source
of sediment in urbanizing areas (U.S. EPA, 1993; U.S. EPA, 1992). Sediment eroded from dirt roads,
construction sites and other cleared areas is the primary pollutant impairing V.I. water quality (DPNR-DEP and
USDA-NRCS, 1998). A 1986 study of erosion rates on St. Thomas and St. Croix estimated erosion from a
disturbed dirt road site to be 591 tons/acre/year (Wernicke, Seymour and Mangold, 1986). Studies of erosion
rates in the Fish Bay watershed on St. John have soil loss from dirt roads of between 100 to 600 tons per year
(MacDonald, et. al., 1997; Sampson, 1997).

Erosion control practices reduce the amount of soil that erodes from construction sites. Sediment control
practices remove eroded soil from stormwater before it leaves the construction site and is deposited onto
roadways and down-slope properties and into guts, ponds and coastal waters. Using erosion and sediment
control practices is an important part of stormwater pollution prevention. These practices have been developed
by the USDA Soil Conservation Service/Natural Resources Conservation Service, various local and state
government agencies, and erosion control professionals and product manufacturers.

The selection of the best soil erosion and sediment control practices for construction sites should be based upon
the nature of the construction activity and the conditions that exist at the construction site. A properly designed
erosion and sediment control plan should:

EROSION CONTROL KEYS
Minimize the amount of disturbed soil on the EROSION CONTROL KEYS
construction site. This will decrease the potential amount The keys to controlling erosion and
of soil that erodes from the site, reducing the number and soil loss on construction sites are to:
complexity of practices needed to remove sediment from .. Protect the soil surface from rain
site runoff. drop impact,
** Maintain soil's water holding
capacity,
SPrevent runoff from off-site areas from flowing .. Slow storm water runoff speed,
across disturbed areas. This will reduce the amount of ** Minimize slope lengths,
stormwater that comes into contact with bare soils. ** Plan to control storm water runoff,
S. Match practices to individual site
Reducing runoff flow over bare soils decreases soil erosion conditions, and
and reduces the volume of stormwater needing treatment Maintain erosion, sediment and
to remove sediment. stormwater control practices.

Slow the runoff flowing across the site. High runoff
velocities reduce water seepage into the soil, increase runoff volume, and cause soil particles to detach
from the soil surface. High runoff velocities can cause severe gully erosion, especially on steep slopes.
Make grades as gradual as possible without excessively modifying existing site conditions.

Remove sediment from on-site runoff before it leaves the site. Because vegetation used for soil
stabilization may not establish itself before a severe storm occurs, on most construction sites it will be
necessary to install practices that can remove sediment from runoff before it leaves the site.

Plan soil disturbance activities for the dry season. This will help to minimize erosion by
scheduling site disturbance activities to occur during times of little or no rainfall.

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How these objectives are met depend upon site characteristics and the type of construction activity. The
following sections describe stabilization and structural practices for erosion and sediment control. Construction
specifications and design procedures for each practice are provided in Appendix B.

3.2 STABILIZATION PRACTICES

Preserving existing vegetation and re-planting cleared/bare soils as soon as possible after earth
change is the most effective way to control erosion. Plant cover reduces erosion potential by:

Protecting the soil surface from the impact of falling rain drops (reducing erosion);
Slowing runoff velocity (or speed) and allowing sediment to settle out (reducing off-site sediment loss);
Physically holding the soil in place with plant roots (erosion control); and
Increasing infiltration (or seepage) rates by improving the soil's structure and porosity.

Vegetative cover can be grass, trees, shrubs, ground covers, other types of plants, or any combination of these.
Grasses are used most commonly because they grow quickly and have fibrous root systems that can rapidly
stabilize soils. Other soil stabilization practices such as mulching or matting may be used during the dry season
when seeds have difficulty establishing themselves. Newly planted shrubs and trees establish root systems more
slowly, so keeping existing ones is a more effective practice. Existing vegetation is adapted to the area, whereas
many exotic plant species that are planted after construction may prove to be less successful.

Vegetative and other stabilization practices can be either temporary or permanent. Temporary practices provide
cover for exposed or disturbed areas for short time periods or until permanent erosion controls are in place.
Permanent vegetative practices are used when soil-disturbing activities are completed or when erosion is
occurring on a site that is otherwise stabilized. It is generally preferable to permanently stabilize disturbed soils
as soon as possible. The stabilization practices presented in this chapter include:

Preservation and Protection of Natural Vegetation
Filter Strips
Land Grading
Surface Roughening
Temporary Seeding
Permanent Seeding and Planting
Mulch, Mats and Geotextiles
Soil Binders/Tackifiers
Soil Retaining Walls
Soil Bioengineering

Stabilization practices should be initiated as soon as practicable in sections of the site where
construction activities have temporarily or permanently ceased, but in no case more than 14 days
after the construction activity in that part of the site has temporarily or permanently stopped.


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Preservation and Protection of Natural Vegetation


The preservation of natural vegetation (existing trees, vines, bushes, and grasses) provides natural buffer zones
to slow runoff and filter sediment. Often areas of a construction site are unnecessarily cleared. Only those areas
essential for construction activities should be cleared (building footprints, road/drive ways, cistern and septic
system areas). Other areas should remain undisturbed, particularly critical areas such as those with steep slopes
and/or highly erodible soils, or areas around guts, ponds or coastal waters.

Preserving natural vegetation on the site by clearing only the area where structures will be built minimizes erosion
potential, protects water quality, provides aesthetic benefits, and is cost-effective in the long term. This practice
is a permanent control practice.


When and Where to Use Natural Vegetation Preservation


This practice applies to all construction sites. Natural vegetation preservation is particularly beneficial in or near
floodplains, wetlands, guts, steep slopes, and other areas where erosion controls would be difficult to establish, install,
and/or maintain. Virgin Islands Law (V.I. Code Annot. Title 12, sections 121 to 125) prohibits "...the cutting or
injury of any tree or vegetation within 30 feet of the center of any natural watercourse, or within 25 feet of the edge
of such watercourse, whichever is greater." This chapter goes further to define a natural watercourse as "...any stream
with a reasonably well-defined channel, and includes streams which have a permanent flow, as well as those which
resultfrom the accumulation of water after rainfalls and which regularlyflow through channels formed by the force
of the waters," i.e., guts. In many instances, guts may flow for only a few days or weeks during the year. However,
the vegetation within or bordering these guts is very important for maintaining water quality and may contain rare,
endangered or threatened plant and animal species.


What to Consider a- ~

"W A*F* PC1..r T;ZSV
On-site vegetation preservation should be planned before any US mM II I
site disturbance begins (Figure 3.1). Preservation requires good .w.. ..
site management to minimize the impact of construction
activities on existing vegetation. Heavy equipment can ruin the
topsoil through compaction and kill desirable plants. The
proposed limits of land disturbance should be
physically marked off to ensure that only the required
land area is cleared. Clearing promotes unwanted weed il zon .,
growth because of increased exposure to sunlight. Hard-to-
control plants like guinea grass, vines, tan-tan and casha cansitnatral
Figure 3.1. Diagram showing site where natural
rapidly take over cleared areas. Hand-clearing preserves existing vegetation is preserved around the perimeter (Toni
vegetation while removing unwanted plants. Thomas, UVI-CES).

Trees to be preserved should be clearly marked and protected from ground disturbances around
the base of the tree. Trees should be protected with tree armoring, fencing, or a tree well (Figure 3.2). Limit
soil placement over existing tree and shrub roots to a maximum of 3 inches. Retaining walls or terraces should
be used to protect roots of trees and shrubs when grades are lowered. Lowered grades should start no closer than
the tree's dripline. Care should be taken to minimize damage to tree limbs and root systems. Contact the


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Department of Planning and Natural TEMPORARY MEASURES NOTE: All protective fencing shall
P extend beyond the tree driDline.
Resources (DPNR), the DPNR SHRUBS FENCE
Division of Fish & Wildlife, the UVI
Cooperative Extension Service (CES),
or the V.I. National Park for
information on rare or endangered TEY AD
TEMPORARY AND PERMANENT T
species before removing trees or other MEASURES FENCING
vegetation.
vegetation. I NOTE: All protective fencing shall extend h vnnd the tra drrinline

Since soils are so shallow in the Virgin FILL AREAS
CUT AREAS
Islands, topsoil is a rare commodity c, '
and should be conserved. As little ORIGINAL
GRADE
existing topsoil should be removed as :;FINAL
possible. Where topsoil has been FINAL GRADEORIGINAL GROUND SURFACE
FINAL .- -. ORIGINAL GROUND SURFACE
removed, soil should be stockpiled on GRADE
the site so that it can be re-applied. IMPROPER PROCEDURE PROPER PROCEDURE
Soil stockpiles must be
temporarily seeded or covered
with a tarp, mat or geotextile to Y- *-
prevent erosion. Compatibility of REL
existing and imported topsoils should
be checked to ensure maximum 1 /'
growth potential for the desired --ULL C
FILL Z *
vegetation. EXCESSIVE CUT AND FILL -
FILL WILL KILL THIS RETAINING WALL
TREE. INNING WALL
Figure 3.2. Tree protection practices (Maryland Department of the Environment, 1994).
How Effective is Natural
Vegetation Preservation?


Preservation and enhancement of natural vegetation is the most effective erosion and sediment control practice.
Any ground disturbance on a site results in increased erosion from that site. By minimizing land clearing to the
areas where final structures will be located (building footprints, driveways, septic systems, etc.), overall site
erosion is minimized. The vegetation remaining on the site also works as a filter to trap sediments and other
pollutants (see Filter Strips). A natural vegetation zone around the building area will also provide a windbreak,
shade, privacy barrier, noise buffer, dust filter, and wildlife habitat. However, other practices may also be needed
to control erosion and sediment loss, especially from roadways or driveways.


ADVANTAGES OF NATURAL VEGETATION PRESERVATIONIPROTECTION
Is inexpensive and already established.
Can handle higher quantities of stormwater runoff than newly seeded areas.
Is already established, therefore is immediately effective.
Has good pollutant filtering capacity since preserved natural vegetation and root structure are usually denser
than in newly seeded areas.
Provides areas for infiltration, reducing stormwater runoff volume and velocity.
Requires less maintenance than planting new vegetation and is more likely to successfully control erosion and
sedimentation.
Holds existing topsoil on ground so that new soil does not have to be brought in.
Provides noise buffers and screens for onsite operations.
Provides a windbreak, shade, privacy barrier, dust filter, and wildlife habitat.
Enhances aesthetics and property values.

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Filter Strips


Filter strips are vegetated strips of land used to remove sediment and other pollutants from stormwater runoff
by slowing runoff speeds, filtering out sediment and other pollutants, and providing some infiltration. Filter strips
are different from buffer strips (as described in Chapter 4) because their effectiveness is not measured by their
ability to improve stormwater infiltration. A filter strip can be an area of vegetation that is left undisturbed during
construction, or it can be newly planted. Filter strips can be either temporary or permanent practices.


When and Where to Use Filter Strips


Filter strips can be used at any site that can support vegetation. Filter strips are best suited for treating runoff
from roads and highways, small parking lots, construction sites and pervious surfaces (CWP, 2000a). Filter strips
are used at the lower edge of cleared or disturbed areas, small parking lots or home sites, or above structural
practices such as swales or diversions. They are particularly effective on flood plains, next to wetlands, ponds and
guts, and on steep unstable slopes. Filter strips should always be used around guts and other drainage
ways, ponds, and coastal waters, and are most effective if they are buffers (see Chapter 4)
consisting of native vegetation left undisturbed during construction. If native vegetation does not
provide enough ground cover, it can be supplemented with native grass seed, such as bahia or hurricane grass.


What to Consider


The type and quantity of pollution that -
filter strips will be treating must be
determined. Slopes, soils, plant species,'
construction timing, watering needs, and '
operation and maintenance methods" : -'
should be considered in designing a filter '
strip. If the filter has outlet flow, it must
be non-erosive. .t0 ael
spreader 6% strip slope le

Filter strips are typically used to treat very Figure 3.3. Vegetated buffer strip design (Schueler, 1987).
small drainage areas. The limiting design factor is the length of flow contributing to the filter strip. The slope
length contributing runoff to a filter strip should not exceed 75 feet for impervious areas (including compacted
soil) or 150 feet for pervious areas (CWP, 2000a). Filter strips are most effective on slopes of 5% or less, and
grassed filter strips should be at least 15 feet wide, forested filter strips should be at least 50 feet wide. Steeper
slopes require wider widths (for example, a 20 30% slope requires a grassed strip at least 25 feetwide, (USDA-
SCS, 1993a).

If filter strips are composed of preserved existing vegetation, good planning and site management are needed to
protect them against disturbances such as grade changes, excavation, equipment damage, and other activities.
Establishing new filter strips requires the establishment of good grass cover, trees and shrubs (see Preservation
and Protection of Natural Vegetation (page 3-3) or Permanent Seeding and Planting (page 3-10)). Careful
maintenance is important to ensure healthy vegetation. The need for routine maintenance like mowing, pruning,
irrigation, and weed and pest control will depend on the species of plants and trees used. Native plant species
will require minimum maintenance while exotic species may require significant inputs (irrigation, pesticides,


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nutrients). Maintaining planted areas may require debris removal and protection against unintended uses or
traffic.


How Effective Are Filter Strips?


Filter strips can be very effective in removing sediment from stormwater if dense plant growth is present (i.e.,
if existing vegetation is preserved or newly planted vegetation grows quickly and thickly). Filter strips can also
slow and reduce stormwater flow through infiltration of excess water so that downstream erosion is greatly
reduced.


ADVANTAGES OF FILTER STRIPS
Filter sediment and other pollutants from stormwater runoff before it reaches drainage channels, guts,
ponds, and/or coastal waters.
Prevent erosion on the vegetated area of the site.
Provide areas for infiltration, reducing the volume and speed of stormwater runoff.
Native (or existing growth) filter strips have lower maintenance requirements.
SAre very low cost if using existing vegetation.
Provide screens and buffers for noise and privacy, provide areas for wildlife habitat and improve site
appearance.
DISADVANTAGES OF FILTER STRIPS
Limit the amount of land area to be used for construction and other activities.
S Require plant growth before they are effective (for newly planted filter strips).
May not be feasible for small lots.




Land Grading


Land grading is the reshaping or alteration of the Ditch or diversion to divert surface flow
existing land surface to provide for better utilization, _;e-n-::
improvllmen Bench
improvement of drainage, and erosion control Gradi Benh 2%
'/ ,- ." -. '- "..,. ..-?. s <-i= Grade = 2% 3%
(Figure 3.4). Land grading requires a well-developed 1",,'," .. -'""-
plan using an engineering survey and layout. The ---i : -' -' < -.'^'"^"\ <"
land grading specification is used to provide for -'--- -- -
Bench to drain to Y "'." =
erosion control and vegetation establishment on stable outlet x n liIi llfi
those areas of the construction site where the
those areas of the construction site where the Figure 3.4. Land grading details (Empire State Chapter, Soil and Water
existing land surface will be disturbed by grading Conservation Society, 1991).
activities.


When and Where to Use Land Grading


Proper land grading practices should be used in all land disturbing activities, and particularly on sites where
surface irregularities, slopes, soil type, obstructions, or wetness interfere with planned uses; or where the desired
land use requires designed land surfaces. Serrated cut slopes (Figure 3.5) should be used for steep cuts
behind buildings or adjacent to driveways or roads to prevent landslides. These slopes can then be


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planted with temporary or permanent vegetation (see Seeding &Planting section). Special attention should be
given to maintaining or improving habitat for rare, threatened or endangered species, where applicable (contact
the DPNR Division of Fish and Wildlife for information on Virgin Islands habitat requirements).


What to Consider
Diversion

The grading plan should incorporate building '
designs and street layouts that fit into and utilize 2
the existing topography, vegetation and other s
desirable natural features to avoid extreme grade -, orm steeper li
modifications. The effect of grading on runoff
quantity and surface storage should be considered. Ditch
Stormwater runoff will be increased by removal of Figure 3.5. Typical section of serrated cut slope (Empire State Chapter
vegetation and surface storage areas (depressions). Soil and Water Conservation Society, 1991).

Water quality will be affected by an increased rate of erosion during construction. Sediment loss will vary with
changes in runoff. Factors determining potential sediment loss (and appropriate control practices) include slope
before and after grading, results of the construction process, and the amount of vegetation re-established on the
graded or shaped site. All disturbed areas MUST be stabilized structurally or vegetatively upon
completion of construction activities.

ADVANTAGES OF LAND GRADING
Minimizes the amount of erosion from graded areas and cut and/or fill slopes.
Prepares land for construction purposes.
DISADVANTAGES OF LAND GRADING
May be difficult on small lots and/or lots with steep slopes.



Surface Roughening


Surface roughening roughens a bare soil surface
with horizontal grooves running across the slope, above is caught l
stair-stepping, or tracking with construction by steps. 2-- 3'
(depending on material) ^[RU
equipment (Figure 3.6). This practice is used to Drainage dependingg on mat
ease establishment of vegetation by seed, to reduce SIF M o tT i7----
stormwater runoff velocity, increase infiltration, --- Greater
than vertical _-- =
reduce erosion, and trap sediment.


When and Where to Use Surface Cit s-
_- Cut slopes with drainage
Roughening to the back. Avoid low spots.


All slopes, especially those steeper than 3:1 (33%), 1iT i lll i Stair Stepping Cut Slopes
require surface roughening to facilitate vegetative Figure 3.6. Surface roughening details stair-stepping (Empire State
stabilization. Chapter Soil & Water Conservation Society, 1991).



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What to Consider I I


There are many different ways to roughen soil Grooving
Grooving6 15
surfaces. Selecting the best method depends on Slopes 115
the type of slope. Steepness, mowing requirements Groove by cutting furrows
(if any), and a cut or fill slope operation are all along the contour. Irregularities
in the soil surface catch rainwater 3"
factors that need to be considered in selecting a and retain seed and fertilizer. r' _
roughening method. A common roughening Figure 3.7. Surface roughening details-grooving (Empire State Chapter
method on moderate slopes is to run the Soil & Water Conservation Society, 1991).
bulldozer/backhoe up and down the slope so that the treads create horizontal indentations (grooving, Figure 3.7).

ADVANTAGES OF SURFACE ROUGHENING
Reduce runoff speed and decrease the distance of overland runoff flow.
Hold moisture better than do smooth slopes and minimize sheet and rill erosion.
DISADVANTAGES OF SURFACE ROUGHENING
May increase cut and fill costs and cause sloughing if excessive water infiltrates the soil.



Temporary Seeding


Temporary seeding is used to reduce erosion and sedimentation on areas that will not be stabilized for a long
time or where permanent plant growth is not necessary or appropriate. A short-term cover of fast-growing
grasses is seeded on a cleared or disturbed site to keep soils from being carried offsite by stormwater runoff or
wind. Seeding can be performed by hydroseeding, hand broadcasting, or installing seeded erosion control mats.
Seeded areas can also be covered with erosion control mats to conserve moisture, prevent wash out, and protect
seeds from birds and insects (see Mulch, Mats & Geotextiles, page 3-11).


When and Where to Use Temporary Seeding


Temporary seeding should be performed no later than 14 days after the halt of construction activities on all
disturbed areas that are likely to be re-disturbed, but not for several weeks or more. This includes denuded areas,
cuts, fills, soil stockpiles, sides of sediment basins, and temporary roadbanks. Temporary seeding should take
place as soon as possible after the last land disturbing activity in an area. It is especially important on
critical areas such as dams, dikes, levees, cuts, fills, and denuded or gullied areas.


What to Consider


Proper seed bed preparation and the use of high-quality seed are needed to grow grass for effective erosion
control. Soil that has been compacted by heavy equipment may need to be loosened with a rake or tiller. Top-
soiling is not necessary for temporary seeding, but it may improve chances for vegetation establishment. Seed
bed preparation may also require fertilizer application to make conditions more favorable to plant growth. Proper
fertilizer application, seeding mixtures and seeding rates vary depending on site location, soil type, slope, and
weather.



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It is very important to select appropriate grass species and to time seeding. Seeding native or naturalized grass
species will increase the odds for success in establishing vegetation. Native species also tend to have lower
maintenance needs because they are adapted to the environmental conditions in the area. The UVI Cooperative
Extension Service or USDA Natural Resources Conservation Service (NRCS, formerly the Soil Conservation
Service) can supply information on suitable native grasses. Local suppliers, the Cooperative Extension Service,
or USDA-NRCS can supply information on best seed mixes and fertilizer and irrigation needs.

Seeded areas on slopes steeper than 4:1 or in sandy, clayey or caliche soils should be covered with mulch or
erosion control mats (see Mulch, Mats & Geotextiles, page 3-11) to provide protection from rainfall and to
prevent birds from eating the seed. Seeded areas should also be mulched and matted if the weather is excessively
dry or if heavy rain is expected before the seed sprouts. Frequent inspections are necessary to ensure that the
grass is growing properly and to determine if irrigation is needed. If grass does not grow quickly or thick enough
to prevent erosion, the area should be reseeded as soon as possible.

Hydroseeding is an erosion control practice used to rapidly "
stabilize disturbed soils with grasses (Figure 3.8).
Hydroseeding equipment is used to uniformly apply a
combination of grass seed, water, fertilizer, mulch and
tackifier to an area to be seeded. Grass seed, paper fiber
mulch, water, and even fertilizer are mixed together in the
hydroseeder tank and then sprayed out over the disturbed
soil area. This equipment allows rapid stabilization of a site .
with a minimum amount of labor. DPNR-CZM owns two "
hydroseeders maintained by the UVI Cooperative -
Extension Service (CES) that are leased to government Figure 3.8. Hydroseeding side slopes and outside rim of a
agencies and the general public upon completion of an sediment basin (Estate New Hernhut, St. Thomas, 1998).
equipment certification workshop. For more information
on the DPNR/UIVI-CES hydroseeding program, contact CES at (340) 693-1080.


How Effective is Temporary Seeding?


This practice, along with Preservation and Protection of Natural Vegetation (page 3-3) and Permanent Seeding
and Planting (page 3-10), is most effective in reducing erosion and sedimentation from a construction site,
especially in areas where soils are unstable because of their slope, texture, structure, a high water table, or high
winds. However, seeding with non-native grasses not adapted to the Virgin Islands climate and soil conditions
may not be as effective due to low survival rate and higher maintenance requirements.

Once vegetation is established, its roots hold the soil in place and the vegetation also slows down runoff, increases
infiltration, and filters sediments from runoff. However, temporary seeding may not be effective in arid and semi-
arid regions (eastern portions of the islands) or during dry seasons (where/when climate prevents fast plant
growth). In those areas, mulch, erosion control mats or geotextiles may be more appropriate for the short term.


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ADVANTAGES OF TEMPORARY SEEDING
Is generally inexpensive and easy to do.
Quickly establishes grass cover when conditions are adequate.
Provides excellent soil stabilization, provides sediment filtering capability, and is visually pleasing.
May help reduce costs of maintenance of other erosion controls (i.e., silt fences, sediment traps/basins may
need to be cleaned out less often).
Reduces stormwater runoff rates and volume.
Hydroseeding has lower labor costs than hand application methods one person can operate a hydroseeder
to apply seed, mulch and fertilizer simultaneously.
Hydroseeding also applies grass seed more evenly, results in faster germination, produces better grass
stands, and provides for easier transportation and storage.
S Improves the appearance of the site.
DISADVANTAGES OF TEMPORARY SEEDING
Depends on adequate rainfall or irrigation for success, especially prior to establishment.
May require fertilizing of plants grown on some soils (particularly caliche), which can be more expensive and
cause downstream water quality problems.
Temporary vegetation requires protection from equipment and heavy use once seeded.




Permanent Seeding and Planting


Permanent seeding and planting is the planting of permanent plant cover such as trees, shrubs, vines, grasses or
legumes on highly erodible or critically eroding areas, or on disturbed soils at the completion of earth change
activities. This practice provides soil stabilization and reduces stormwater runoff and sediment loads to guts and
coastal waters by slowing runoff velocity and increasing runoff infiltration. Vegetation also filters sediment and
other pollutants, improves wildlife habitat, and enhances the appearance of a site and its property value.


When and Where to Use Permanent Seeding & Planting


Permanent seeding and planting should be used to stabilize all disturbed areas once construction
has been completed in that area. Permanent vegetation
establishment is especially important on steep slopes and grades, in
filter strips, buffer areas, and vegetated sales, and along guts,
ponds and coastal areas.


What to Consider


It is very important to select appropriate plant species and to
carefully time planting. Planting native or naturalized species will
increase the odds for success in establishing vegetation. Native
species also tend to have lower maintenance needs because they are
adapted to local environmental conditions. Many low-maintenance,
native plants can be added to the site's landscaping (Figure 3.9).
Some good native plants available in local nurseries include wild Figure 3.9. A low-maintenance, natural landscape in
a dry area (Estate Nazareth, St. Thomas, 1995).


Chapter 3


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Environmental Protection Handbook


3-10









frangipani, orange man jack, pink cedar, sea grape, lignum vitae, turpentine tree, teyer palm, sabal palm, wild
ferns, wild anthurium, and spider lily.

Some exotic plants can also be incorporated into the landscape. Be
careful to choose species that won't escape into natural areas and
crowd out native plants. Vetiver grass (Vetiveria zizanioides) hedges
can be planted across slopes (along the contour) to form a living
terrace (Figure 3.10). Vetiver is a non-native, non-invasive,
clumping grass species. It is used in Africa, India and Southeast Asia
to stabilize slopes and channels by trapping sediment behind thet
grass. Some exotic ornamental plant species that can be used around Figure 3.10. Newly planted vetiver hedge (UVI St.
the home include hibiscus, bougainvillea, oleander, croton, Thomas, 1999).
heliconia, ginger, isora, aralia, agave, and non-native palms. Fruit
trees and vegetable gardens can also be planted once construction is completed. The UVI Cooperative Extension
Service (CES) or USDA Natural Resources Conservation Service (NRCS, formerly the Soil Conservation Service,
SCS) can supply information on suitable native and exotic plant species. Local suppliers, CES or USDA-NRCS
can supply information on best seed mixes and fertilizer and irrigation needs.

ADVANTAGES OF PERMANENT SEEDING & PLANTING
Quickly establishes vegetative cover when conditions are adequate.
Provides excellent soil stabilization and sediment filtering capability.
Improves stormwater infiltration, reducing stormwater runoff speed and volume.
Provides a windbreak, shade, privacy barrier, dust filter, and wildlife habitat.

Improves site appearance and property values.
DISADVANTAGES OF PERMANENT SEEDING & PLANTING
Depends on adequate rainfall or irrigation for success.
May require fertilizing of plants grown on some soils (particularly caliche), which can be more expensive and
cause downstream water quality problems.
Permanent vegetation requires protection from equipment and heavy use once seeded.



Mulch, Mats and Geotextiles


Mulching is a temporary soil stabilization or erosion control practice. Mulching uses materials such as cut grass,
woodchips, wood fibers, straw, or gravel to cover the soil surface to temporarily stabilize disturbed areas until
vegetation is established or construction is completed. Mulching also reduces the speed of stormwater runoff over
bare soils. When used together with seeding and planting, mulching can aid in plant establishment by holding
seed, fertilizer, and topsoil in place; by helping to retain moisture; by insulating against high temperature, and
by protecting seed from birds.

Erosion control mats are materials (straw, coconut, wood, or synthetic fiber) that have been woven into a mat
or blanket and are backed with plastic or jute netting. Erosion control mats offer the same benefits as mulch but
are more stable and can withstand much higher stormwater velocities than loose mulch. They are used to
temporarily stabilize bare soils or slopes during construction when it is difficult to establish temporary vegetation
(due to dry, stony, or steep soil conditions). Mats are also used with permanent seeding and planting to help hold



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soils in place until grass or other plants can become established. Figure 3.10 shows how erosion control mats
are used for erosion control in a drainage swale.

Netting is typically made from jute, coconut or other wood fiber, plastic, paper or cotton and can be used to hold
mulch onto the ground. Netting can also be used alone to stabilize soils while plants, such as ground covers,
become established. However, it does not retain moisture or temperature well.

Other materials, called filter fabrics or geotextiles, are also used for erosion control. These materials are made
by weaving or bonding fibers made from synthetic materials such as polyester, nylon, polyvinyl chloride (PVC),
or other material. Mats, netting and other filter fabrics are used in areas with steep slopes where loose mulch
and seed are vulnerable to being washed away, or where vegetation is difficult to establish.


When and Where to Use Mulch, Mats and Geotextiles


Loose mulch should only be used on fairly level slopes, or in areas that l
only need short-term stabilization. Erosion control mats or geotextiles
are often used alone in areas where temporary seeding cannot be used
because of season or soil/slope conditions. Mats can provide immediate,
effective erosion control. In critical areas such as drainage swales .
channels, or along shorelines, mats or geotextiles can be used to provide .
channel stabilization. There are many different types of erosion control
mats. Erosion control mats can be used for a wide range of slopes and
stormwater flow rates. For example, 100% straw mats can be used on
slopes up to 3:1 in steepness and 75 feet in length or in low-flow swales
(Figure 3.11). Straw/coconut mats can be used on steeper slopes (2:1 -
1:1, depending on length) and medium flow discharge channels.
Coconut fiber or synthetic mats provide long term protection on steeper
slopes or in high discharge channels. Check the manufacturer's Figure 3.11. Straw mat used to stabilize
specifications to determine which material is appropriate for a given seeded slope (UVI St. Thomas, 1999).
application.

Geotextiles can be used alone as matting to stabilize flow in channels and swales, to protect seedlings on recently
planted slopes, or to protect tidal or drainage banks where moving water may wash out new plantings. When
properly anchored, geotextiles can provide stabilization on slopes up to 30-40% (depending upon material type).
Geotextiles are also used as separators. For example, filter fabric can be placed between gravel or rip-rap and
soil. This i!.h. i,''g" prevents the gravel from being compacted into the underlying soil and prevents the soil
underneath the rip-rap from being eroded.


What to Consider


Mulch should be applied to moderate slopes (< 10%) and soils that are not highly erodible. On steep slopes,
highly erodible soils, or in swales (see sections on Drainage Swales and Grassed Swales) erosion control mats
or geotextiles should be used and anchored into place with staples (anchoring patterns depend on slope steepness
and length and flow rate, see Figure 3.12). On extremely arid sites where grasses cannot survive, native ground
covers or shrubs can be planted in jute or coir (coconut fiber) netting. Filter fabric or erosion control mats can


Chapter 3


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Environmen tal Protection Handbook


3-12









also be used for this purpose. Before stabilizing an /
area, it is important to have all sediment controls CROSS-SECTION
installed and for runoff to be diverted away from
the area to be planted. .'' 7

Final grading is not necessary before mulching. '.*
Mulched areas should be inspected often to find
where mulch has been loosened or removed. cips whoer ttingor
S1, / more strip widths are
These areas should be reseeded, if necessary, and required. Attach
staples on-18" centers
the mulch cover replaced immediately. -
Staple outside
edge of matting Staple outside
on 2" centers S' edge of matting
When selecting erosion control mats or on 2" centers
geotextiles, choose an appropriate type for the 2
intended use. Follow manufacturer
recommendations or seek advice from the USDA
Natural Resources Conservation Service or the Figure 3.12. An example of erosion control matting of a drainage swale
UVI Cooperative Extension Service. Areas covered (Maryland Department of the Environment, 1994).
with mats or geotextiles should be inspected
regularly to determine if cracks, tears, or breaches have occurred. If so, repairs should be made immediately.

Effective netting and matting requires firm and continuous contact between the fabric and the soil. If there is
no contact, the material will not hold the soil in place and erosion will occur underneath it. Matting should be
able to withstand stormwater runoff speeds of up to 5 feet per second.


How Effective are Mulch, Mats, and Geotextiles?


Mulch, mats and geotextiles are very effective in reducing erosion and are very cost-effective, as compared to
retaining walls or purchasing new top soil. Mulch alone should only be used for temporary protection of the soil
surface on fairly level slopes. The useful life of mulch, mats and geotextiles varies according to the material and
amount of rainfall, from a minimum of 1 month for mulch to 3 years for geotextiles.


ADVANTAGES OF MULCH, MATS AND GEOTEXTILES
SProvide immediate, effective protection of exposed and/or eroding soils.
SMulch, mats and geotextiles retain moisture, minimizing the need for watering.
Organic mulch, mats and netting do not need to be removed because they are biodegradable.
SMats protect seeds from birds and other animals.
SMats and geotextiles are less expensive than structural practices and a wide variety are available to match
specific needs.
SAre convenient to install.
DISADVANTAGES OF MULCH, MATS AND GEOTEXTILES


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SMulch and/or mats may delay seed germination in some species.
SMulch can be easily blown or washed away by runoff if not secured.
SMats are difficult to anchor into stony or compacted clay soils.
SMats may inadvertently contribute to weed growth, since they hold in moisture.
Geotextile effectiveness may be reduced significantly if the fabric is not properly selected or installed.
SMany eotextiles are photodegradable and must be protected prior to installation.



Soil Binders/Tackifiers


Soil binders or tackifiers are chemical polymers or emulsions sprayed onto the soil surface to provide soil
stabilization. There are many different types of chemical polymers on the market that provide varying degrees
of stabilization. Soil polymers are used for temporary erosion control, and are typically applied using
hydroseeding equipment, with or with out seed and/or mulch.


When and Where to Use Soil Binders/Tackifiers


Soil binders are often used on extreme slopes and drought (very dry) soils where it is difficult to establish
vegetation. Tackifiers are typically used in conjunction with hydroseeding (see Temporary Seeding page 3-8) to
stabilize soils and hold grass seed and mulch in place until germination and root establishment occurs. Binders
and/or tackifiers can also be used to hold loose mulch in place on soils. Some tackifiers and binders can also help
to conserve moisture in soils. These chemicals are also effectively used on construction sites for dust suppression.


What to Consider


There are many different types of soil binders and tackifiers available. Some materials are more toxic than others,
and some may or may not be biodegradable. The type of material chosen depends on the site's slope and soils,
the season and geographic area of the site (for example, whether the site is on the dry east end or wetter north
side of an island), the longevity of the material, whether or not seed and/or mulch will be applied with the
material, and whether or not it is an acceptable material to be used in the hydroseeding equipment. Products
should be carefully investigated. Practice application/installation varies by manufacturer; see manufacturer
guidelines for specific installation specifications. The International Erosion Control Association (IECA) website
provides a partial list of erosion control product vendors at: www.ieca.org.

ADVANTAGES OF SOIL BINDERS/TACKIFIERS
Provide short-term stabilization of severe, dry and/or stony slopes that are difficult to vegetate.
SCan provide stabilization for 2 to 18 months, depending on the material and site conditions.
SAre useful for holding seed, mulch and fertilizer in place on steep slopes.
Aid in conserving soil moisture.
Provide excellent dust control.
SSome are non-toxic and/or biodegradable.

DISADVANTAGES OF SOIL BINDERS/TACKIFIERS


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Many are not suitable for long term stabilization (over 6 months).
SSome may be toxic or persist in the environment.
Some forms may clog hydroseeding equipment used to apply material.
Do not prevent mass-wasting (landslides).



Soil Retaining Walls


Soil retaining walls are structures used to hold loose or unstable soil firmly in place. For example, soil tie backs
and retaining walls can be used during excavation to prevent cave-ins and accidents, but they also are excellent
permanent erosion control practices that retain soils and slopes to prevent them from moving. There are many
different types of soil retaining structures that can be used. Some basic ones include:

Skeleton Sheeting: Skeleton sheeting is the least expensive soil retaining system. It requires the soil
to be cohesive (like clay). Construction grade lumber is used to brace the excavated face of the slope.
This is a temporary practice.

Continuous Sheeting: Continuous sheeting uses a material such as steel, concrete or wood to cover
the face of the slope in a continuous manner. Struts and boards are placed along the slope to provide
continuous support to the slope face.

Permanent Retaining Walls: Permanent retaining walls may be necessary to provide support to the
slope after construction is completed. Concrete, stone, or wood (horizontal telephone poles, etc.)
retaining walls can be built and left in place.


When and Where to Use Retaining Walls


Soil retaining walls should be used where other
methods of soil retention are not practical. They are
especially applicable in the Virgin Islands to retain cut
slopes along road and drive ways, parking lots, building
sites, and other cut and fill areas where slopes or soils
are not suitable for vegetative stabilization (Figure
3.13).


What to Consider


~- ;;;;-;;;;;;-;- 4


I--




Figure 3.13. Rock retaining walls installed to stabilize base of steep
slope above a sediment basin (Estate New Hernhut, St. Thomas,
2000).


Soil retaining walls are used for both erosion control and safety purposes. Retaining wall design must address
foundation bearing capacity, sliding, overturning, drainage, and loading systems. These are complex systems and
all but the smallest retaining walls should be designed by a licensed engineer.


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ADVANTAGES OF RETAINING WALLS
Provide safety to workers.
Can be used as either temporary or permanent structures (depending upon design).
Are exceptionally effective in preventing erosion and landsliding from unstable slopes and soils that cannot
be stabilized using conventional methods.
DISADVANTAGES OF RETAINING WALLS
S Require the expertise of a professional engineer for all but the smallest retaining walls.
May be expensive to design and install, depending upon site constraints, size and material used.



Soil Bioengineering


Soil bioengineering combines mechanical, biological and ecological concepts to stop and prevent shallow slope
failures (or landslides) and erosion. The soil bioengineering practices discussed in this section can be divided into
two general categories: living and non-living.

The living approach uses live plants to provide soil reinforcement and prevent surface erosion. Vegetated rock
gabions and vegetated rock walls use porous structures with openings that plant cuttings are inserted into. The
rock provides immediate resistance to sliding, erosion and washout. As the vegetation becomes established, roots
bind the slope together into a unified mass.

Non-living approaches use rigid structures, like gravity retaining walls and rock buttresses to retain soil. Plants can
be used in conjunction with these structures to create vegetated structures. The plants enhance the structures
and help to reduce surface erosion.


When and Where to Use Soil Bioengineering


Soil bioengineering techniques are generally appropriate for immediate protection of slopes against surface
erosion and shallow mass wasting (landslides), and provide cut and fill slope stabilization, earth embankment
protection, and small gully repair treatment. These techniques are used when vegetative stabilization alone is not
feasible. The use of soil bioengineering practices is limited on rocky or gravelly slopes that lack sufficient soil or
moisture to support plant growth. Soil-restrictive layers, such as hardpans, may also prevent root growth.


What to Consider


Soil bioengineering is often a useful alternative for small, highly sensitive, or steep sites where the use of
machinery is not feasible and hand labor is a necessity. However, rapid vegetative establishment may be difficult
on extremely steep slopes. The soil bioengineering system selected should fit the site. The slope, soils, geology,
hydrology and existing vegetation should be taken into account when designing the system. Existing vegetation
should be retained whenever possible to provide protection against surface erosion and shallow slope failures.
This vegetation can also be a source of cuttings to use in the practice. Native plant species that root easily should
be used (turpentine tree (Bursera simaruva), white manjack (Cordia sulcata), hog plum (Spondias mombin), orchids,
bromeliads, anthuriums see USDA-NRCS Common Tlh.,,mj Table) or contact the USDA Natural Resources
Conservation Service, UVI Cooperative Extension Service, or the V.I. Department of Agriculture for information
on appropriate plants. The following soil bioengineering practices are most appropriate for conditions in the


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Virgin Islands, although other practices may be applicable (consult the USDA-NRCS for further information on
soil bioengineering practices).


Vegetated Rock Gabions: Rock gabions are
rectangular baskets made from triple-twisted,
hexagonal mesh of heavily galvanized steel wire
placed in position, wired to adjoining gabion
baskets, filled with large stone, and then folded
shut and wired at the ends and sides. Live
branches (or seeds) are then placed on each
consecutive layer between the rock-filled baskets.
These branches will take root inside the gabion
basket and in the soil behind the baskets, binding
the gabions to the slope (Figure 3.14).


This practice is used at the base of a slope where
a low wall may be needed to stabilize the toe of
the slope and reduce its steepness. It is not
designed to resist large, lateral earth stresses.
Vegetated rock gabions should be built a
maximum of 5 feet in height, overall, including
the excavation needed for a stable foundation.
This practice is useful where space is limited and
a more vertical structure is needed.


Vegetated Rock Wall: A vegetated rock wall is a
combination of rock and live branch cuttings used
to stabilize and protect the toe of steep slopes.
Vegetated rock walls are different from retaining
walls because they are placed against relatively
undisturbed earth and are not intended to resist
large lateral earth pressures (Figure 3.15).
Vegetated rock walls are used where a low wall
maybe needed to stabilize the toe of the slope and
reduce its steepness. This practice is especially
useful where space is limited and natural rock is
available.


Low wall/slope face plantings: This practice
consists of a low retaining wall placed at the foot
of a slope so that the slope can be flattened for
planting. Vegetation established on the face of the
slope protects against both surface erosion and
shallow land slides (Figure 3.16). Different types
of retaining walls can be used as low walls, the
simplest being a gravity wall that resists lateral
earth movement with its weight or mass. This
includes masonry and concrete walls as well as
reinforced earth or geogrid walls.


Figure 3.14. Vegetated rock gabion details (USDA-SCS, 1992). (Note:
rooted/leafed condition of the living plant material is not representative of
the time of installation).
Cross Section



,Ib -




Rock placed with I *-
16 batterand ^ c Rock wall
3 point bearing (max 5-foot height)

Live branch cuttings
Ground line (112 to 1 nch diameter)


2- --

C 0
oo O
Figure 3.15. Vegetated rock wall details (USDA-SCS, 1992). (Note:
Rooted/leafed condition of the living plant material is not representative
of the time of installation).

Cross section
not to scale
Vegetative plantings Origiil



Low wall
1 Regraded slope



S f -
4 -- Compacted fill material


Figure 3.16. A low wall with plantings established on the slope above
(USDA-SCS, 1992).


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Cross section
not to scale
.










Ground line r-


, Gabion baskets


Drain


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, i,. l.. l., : l










Tiered wall/bench plantings: An alternative to a low wall with a face planting is a tiered retaining wall, or terrace,
system. This alternative effectively allows vegetation to be planted on slopes that would otherwise be too steep.
Shrubs and trees planted on the benches screen the structure behind them and lend a more natural appearance
while their roots protect the benches. Virtually any type of retaining structure can be used in a tiered wall system.
A tiered wall system allows plant propagation on steep slopes and embankments.


ADVANTAGES OF SOIL BIOENGINEERING
Soil bioengineering systems generally require minimal access for equipment and workers and cause
relatively minor site disturbance during installation.

Combined slope protection systems can be more cost-effective than the use of either vegetative treatments
or structural practices alone, especially when using indigenous plant material.

Are exceptionally effective in preventing erosion and landsliding from unstable slopes and soils that cannot
be stabilized using vegetative methods alone.

Can withstand heavy rainfalls immediately after installation.

Is self-repairing by regeneration and growth once vegetation is established.

Requires little maintenance.
DISADVANTAGES OF SOIL BIOENGINEERING
May be expensive to design and install, depending upon site constraints, size and materials used.

Depending on the species of plant material used, may be difficult to get adequate vegetation establishment.

Requires periodic inspections until vegetation is established.


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3.3 STRUCTURAL PRACTICES

Structural practices are used in sediment and erosion control to divert stormwater runoff away from exposed
areas, to convey runoff, to prevent sediment from moving offsite, and to reduce the erosive forces of runoff
waters. These controls can be either permanent or temporary practices, depending on how they are used. The
structural practices described in this chapter include:

Perimeter Dike/Swale Check Dams/Triangular Dikes/Berms
Drainage Swale Sediment Traps
Temporary Storm Drain Diversion Temporary Sediment Basin
Silt Fence Storm Drain Inlet Protection
Gravel/Stone Filter Berm Outlet Protection
Stabilized Construction Entrance Gabion Inflow Protection

Temporary structural practices are used during construction to prevent sediment from moving offsite. The length
of time that temporary practices are functioning varies since the sediment control t tl may change as
construction activities progress. Permanent structural practices are used to convey stormwater runoff to a safe
outlet away from erodible areas and/or to treat stormwater runoff to remove sediment. Permanent structural
practices remain in place and continue to be used after construction is completed.

In general, structural sediment control practices are less effective that erosion control- i.e., it is much easier and
more cost effective to keep the soil in place than it is to attempt to remove soil from stormwater. This is
particularly true in the Virgin Islands since predominant soil types have high clay content. Clays are particularly
difficult to remove from stormwater because of their very small particle size and propensity to stay suspended
in stormwater for long time periods. Most practices, such as silt fences, sediment traps, and
gravel/stone filter berms, are not effective in removing clays from stormwater runoff.



Perimeter Dike/Swale


A perimeter dike is a ridge of compacted soil. A swale is an excavated trench or channel. These two practices are
used together to prevent stormwater runoff generated outside a construction site from entering and crossing the
site and eroding bare soils or disturbed areas. Perimeter dikes and swales reduce the volume and speed of runoff
on a site and channel stormwater to a stabilized discharge area or sediment trap (see sections on Sediment Traps
and Temporary Sediment Basins). The dike is built using the soil dug from the adjoining swale placed along the
perimeter of the construction site or disturbed area. Dikes and swales can be either temporary or permanent
stormwater control structures.


When and Where to Use Perimeter Dikes/Swales


Perimeter dikes/swales are generally built around the edge of the site before any earth change activity takes place.
They may also be used to protect existing buildings, topsoil stockpiles, or other small areas that have not yet been
fully stabilized. They are appropriate for sites less than or equal to two (2) acres in size.


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What to Consider


If temporary dikes and swales are to remain'-
TRAPEZOIDAL CROSS-SECTION
in place longer than 10 days they must be
stabilized using either vegetation, erosion
control matting, geotextile, rip-rap, or some -_
other material. The distance from the bottom of
the swale to the top of the dike should not be less PARABOLIC CROSS-SECTION
than 18 inches. The bottom width of the dike and Figure 3.17. Examples of perimeter dikes/swales (U.S. EPA, 1992).
width of the swale should be a minimum of three
(3) feet. The maximum allowable grade should NOT exceed 20 percent. Figure 3.17 shows two different types
of perimeter dike/swale.

Stormwater runoff diverted by a perimeter dike/swale should be directed to an appropriate area for sediment
removal (a sediment trap, basin, or filter area: see sections on Sediment Traps, Sediment Basins, and Filter
Strips). Temporary perimeter dikes/swales may stay in place as long as 12 to 18 months, provided they are
properly stabilized and inspected and maintained on a regular basis. They should remain in place until the area
they were built to protect is permanently stabilized. Temporary and permanent control practices should be
inspected once a week on a regular schedule and after every large or intense rain storm. Repairs should be made
promptly.

ADVANTAGES OF PERIMETER DIKES/SWALES
Are easy to install and are effective for channeling stormwater runoff away from areas subject to erosion.
Can handle flows from large drainage areas.
Are inexpensive because they use materials and equipment normally found onsite.
DISADVANTAGES OF PERIMETER DIKES/SWALES
Can cause erosion and sediment transport downstream if they are not properly designed, built or stabilized.
If water flows too fast, vegetation may be difficult to establish slopes less than 20% are recommended.
Require frequent maintenance, inspections and repairs.



Drainage Swale


A drainage swale is a channel excavated and located to convey runoff to a desired location. It typically has a lining
of vegetation, erosion control matting, geotextile, rip-rap, concrete, or some other material.


When and Where to Use Drainage Swales


A drainage swale is used to route stormwater around or through an area without causing erosion. A swale can
convey runoff from an undisturbed area surrounding the construction site to a stabilized outlet, where runoff
is discharged at non-erosive rates. It can also be used to divert sediment-laden runoff away from a disturbed area,
across disturbed areas to shorten overland flow distances, or from the base of a slope to a sediment trapping
device.


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Chpe rso n edmn oto rcie


What to Consider


2:1 or flatter
Cmin. / Existing
ground
D min. LEV


Swales should be lined with grass, sod, erosion swaleA wale B CROSS SECTION
control mats, geotextiles, rip-rap, or concrete. The 1' 6 FLOW
FLOW 0 5%orsteeper, dependent on topography i
type of liner used is dependent on the volume and F-LO t
Outlet as required
velocity of the stormwater runoff to be conveyed. PLAN VIEW
The swale should have a positive grade and should PLAN VIEW
have no dips or low points where stormwater can Figure 3.18. Temporary swale design example (Empire State Chapte
Soil and Water Conservation Society, 1997).
collect. Figure 3.18 shows an example of swale
design and Table 3.1 provides an example of how to design two different sized drainage swales.


Table 3.1. Example drainage swale designs (Empire State Chapter, Soil and Water Conservation Society, 1997).

Swale A Swale B

Maximum Drainage Area Contributing Runoff < 5 Acres 5 10 Acres

Bottom Width of Flow Channel 4 feet 6 feet

Depth of Flow Channel 1 foot 1 foot

Side Slopes 2:1 (50% or 26)or flatter 2:1 or flatter

Grade 0.5% minimum 0.5% minimum
20% maximum 20% maximum




ADVANTAGES OF DRAINAGE SWALES
Swale excavation can be easily performed with earth moving equipment.

SCan transport large volumes of runoff.
DISADVANTAGES OF DRAINAGE SWALES
Stabilization and design costs can make construction expensive.

Effective use is restricted to areas with relatively flat slopes (< 8% for most designs).




Temporary Storm Drain Diversion


A temporary storm drain diversion is a pipe that redirects an existing storm drain system or outfall channel so
that it discharges into a sediment trap or basin.


When and Where to Use Temporary Storm Drain Diversions


Storm drain diversions should be used to temporarily divert stormwater runoff flow going to a permanent outfall.
This diverted flow should be directed to a sediment trapping device (see Sediment Traps or Temporary Sediment
Basins section). A temporary storm drain diversion should be used for as long as the area draining to the storm
drain remains disturbed.


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r,










What to Consider


Since the existing storm drain system will be modified, careful consideration needs to be given to the pipe
configuration and the resulting impact of installation. The temporary diversions will need to be removed once
construction is completed and the original storm drain system is restored. Therefore, appropriate restoration
measures should be taken, such as flushing the storm drain before removing the sediment trapping device, and
stabilizing the outfall and restoring grades.

ADVANTAGES OF TEMPORARY STORM DRAIN DIVERSIONS
Requires little maintenance once installed.
DISADVANTAGES OF TEMPORARY STORM DRAIN DIVERSIONS
SDisturbs existing storm drain patterns.



Silt Fence


A silt fence, or filter fabric fence, is a temporary practice for sediment control. A silt fence is made ofgeotextile
or filter fabric stretched across wood posts, rebar or a wire support fence. The lower edge of the material is
vertically trenched into the ground and covered by backfill. Silt
fences are most effective for removing sediment from overland
flow. They reduce sediment loads entering receiving waters. NO YES
They are also used to catch wind blown sand and to create an
anchor for sand dune creation. Along with the typical wooden
post and filter fabric method, there are several variations of Sediment
filter fabric fence installation including fencing that can be
purchased with pre-sewn pockets for use with steel rebar fence
posts. (Use of steel rebarforfence posts is recommended in the Sediment
Virgin Islands, especially on slopes greater than 20% or in
stony or clayey soils).


Figure 3.19. Poor silt ence placement (left) vs. proper silt
fence placement (right) (Fifield, 1996).


When and Where to Use Silt Fences


Silt fences are the most widely and most incorrectly used
sediment control practice in the Virgin Islands.

Silt fences should only be used to detain sediment on small construction
sites, such as individual home sites. Silt fences should be installed prior
to earth change activities. The fence should be placed away from the
bottom of the slope (to increase holding capacity), along a line of
uniform elevation perpendicular to the direction of flow (Figure 3.19).
Silt fence material MUST be trenched into the ground to work properly
(Figure 3.20). Fencing can also be placed across the direction of
stormwater flow at the outer boundary of the work area. Silt fences
should NEVER be installed in guts or swales.


Figure 3.20. Properly installed reinforced silt
fence note trenching, wire mesh and steel
bars (Estate Caret Bay, St. Thomas, 1999).


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Silt fences used on slopes greater than 20% (5:1 or, or installed in rocky or clayey soils, should use /," 2" steel
rebar stakes instead of wooden posts (Figure 3.21). Silt fences installed on slopes greater than 40% should use
/8" 2" steel rebar and wire mesh backing to prevent the fence from being knocked down by heavy stormwater
flows. Double the height of the silt fence on slopes steeper than 1:1 or with a
greater than recommended slope length (see Table 3.2). Attach the top and
bottom of the second layer of geotextile to the rebar and wire mesh so that it
overlaps the first layer by 6 inches. Staple the two layers together. .


What to Consider


A silt fence is NOT appropriate for controlling runoff from a large area i( i
than 5 acres). However, this type of fence is much more effective than a straw
bale barrier if properly installed and maintained. (Straw bale barriers are NOT
recommended for use in the Virgin Islands). Silt fences MUST be anchored and
trenched into the ground or else they will fail. They should always be used in
combination with other erosion and sediment control practices, such as
temporary seeding, perimeter dikes and swales, drainage swales, sediment traps,
etc. The area below a silt fence should be undisturbed ground.


The effective life span for a silt fence depends on the material and
maintenance. Silt fences require frequent inspection and prompt
maintenance to maintain effectiveness. The fence should be
inspected after each rainfall. Check for areas where runoff has
eroded a channel beneath the fence, or where the fence has
sagged or collapsed from runoff flowing over the top. Remove
sediment when it is one-third to one-half the height of the fence,
or after each storm. (Accumulated sediment can be used for
landscaping purposes once construction is completed.) Table 3.2
lists maximum slope lengths (distance down-slope between silt
fences) for a silt fence depending upon steepness.


Figure 3.21. Properly installed silt
fence (Estate St. George's Hill, St.
Croix, 1998).


Table 3.2. Maximum allowable slope lengths
contributing runoff to a silt fence (Empire State Chapter,
Soil and Water Conservation Society, 1997).
Slope Steepness Maximum Slope Length
(feet)
2:1 (50% or -260) 50
3:1 (33% or -190) 75
4:1 (25% or -14o) 125
5:1 (20% or -11) 175
Flatter than 5:1 200


Maximum drainage area for overland flow to a silt fence should not exceed V acre per 100 feet of fence. Also, do
not use silt fences to retain sediment from concentrated stormwater flow (such as in a channel, gully, gut or other
drainage way), the material is not designed and manufactured to withstand the force of concentrated flows.


ADVANTAGES OF SILT FENCING
Reduces the speed of stormwater runoff and removes some sediment from runoff, protecting downstream
areas from sedimentation.
Is inexpensive and easy to install.
Is suitable for smaller developments (such as individual home sites or those less than 5 acres).
Requires minimal clearing and grubbing for installation.
DISADVANTAGES OF SILT FENCING
Is not suitable for larger developments (greater than 5 acres).
Un-reinforced (no steel rebar, wire netting) silt fences are not suitable for slopes greater than 20%.
Fences with wood stakes are difficult to install in stony or clayey soils use steel rebar stakes instead.
SWILL FAIL IF IT IS NOT PROPERLY ANCHORED AND TRENCHED INTO THE GROUND!
Requires frequent inspection and maintenance to ensure effectiveness.

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Gravel/Stone Filter Berm


A gravel, stone or rock berm is a temporary barrier of loose gravel, stone, or rock built across the bottom of a
slope to slow runoff from leaving a site. They can also be used to divert flow from an exposed traffic area. These
berms can also be used for directing runoff from a right-of-way to a stabilized outlet.


When and Where to Use Filter Berms


Gravel or stone filter berms are used where roads and other rights-of-way under construction accommodate
vehicular traffic. They are meant for use in areas with gentle slopes. They also may be used at traffic areas within
a construction site. Berms should be used in conjunction with other temporary sediment control
practices, such as diversion dikes and swales, drainage swales, silt fences, temporary seeding,
and/or sediment traps.


What to Consider Coare aggregates


Berm spacing depends on the steepness of the 5
slope berms should be placed closer- i I- Vu-70 -
together as the slope increases. The berm
should be inspected regularly after each
should be inspected regularly after each Figure 3.22. Example of a gravel filter berm (U.S. EPA, 1992).
rainfall, or if breached by construction or
other vehicles. All needed repairs should be performed immediately. Accumulated sediment should be removed
and properly disposed of and the geotextile or filter material replaced, as necessary (Figure 3.22).

ADVANTAGES OF FILTER BERMS
SReduce the speed of stormwater runoff.
Berms are fairly inexpensive and easy to install, and work well on slopes up to 40%.
DISADVANTAGES OF FILTER BERMS
Have a limited life span.
Can be difficult to maintain due to clogging with mud.
Frequent inspection and maintenance is necessary to ensure effectiveness.



Stabilized Construction Entrance


A stabilized construction entrance is a section of the construction road adjacent to a paved road that is stabilized
with geotextile and large stone or gravel. A stabilized construction entrance is designed to reduce the amount
of soil tracked off of the construction site by vehicles leaving the site. The rough surface of the stone or gravel
shakes and pulls the soil off of vehicle tires as they drive over the entrance. The stone also reduces erosion and
rutting on the portion of the road that it is installed on by protecting the soil below. Filter fabric or geotextile
separates the stone from the underlying soil, preventing the stone from being ground into the soil. The fabric
also reduces rutting caused by vehicle tires by spreading the weight of the vehicles over a larger soil area than the
tire width.


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When and Where to Use Stabilized Construction Entrances


A stabilized construction entrance should be installed at every point where traffic enters or leaves a construction
site before construction begins on the site. For individual home sites, the construction entrance should be
located where the permanent driveway will be sited. Stabilized construction entrances should not be used on
existing pavement.
50' minimum Existing
|pavement
What to Consider r -min
What to C DrrfiI- Mountable berm
Filtercloth Profile I (optional)
50' min.
Stabilized construction entrances Existing
Ground E
should be wide and long enough
so that the largest construction -
7. *. Existing
vehicle will fit in the entrance 1,mi. pavement
with overlap available. A good as -
rule of thumb is for the entrance
to be a minimum of 50 feet long Plan View
(30 feet for an individual home
site) and 10 feet wide with a flare Figure 3.23. Stabilized construction entrance design (Empire State Chapter, Soil and Water
Conservation Society, 1997).
at the existing road to provide
turning radius. Stone, rock or gravel (2" 3") should be placed at least 6 inches deep on top ofgeotextile over
the length and width of the entrance (Figure 3.23).


ADVANTAGES OF STABILIZED CONSTRUCTION ENTRANCES
Are very effective in reducing the amount of soil tracked off of a construction site.
Can improve the appearance of the construction site from the public's point of view.
DISADVANTAGES OF STABILIZED CONSTRUCTION ENTRANCES
SOnly work if they are installed at every location where traffic leaves and enters the site.
Cannot always remove all of the soil tracked off of disturbed areas by vehicles.
Stone may have to be added to maintain effectiveness.



Check Dams/Triangular Dikes/Berms


A check dam is a small, temporary or permanent dam constructed across a drainage ditch, swale, or channel to
reduce the speed of concentrated flows. Reduced runoff speed reduces erosion and gullying in the channel and
allows sediments to settle out.


When and Where to Use Check Dams


A check dam should be installed in steeply sloped swales or channels, or in swales where adequate vegetation
cannot be established. Check dams limit erosion by reducing flow in small open channels that are degrading or
subject to erosion. A check dam may be built from stone, rip-rap, pea gravel-filled sand bags, or manufactured
pervious berms or barriers such as a Triangular Silt Dike (Figure 3.24), EnviroBerm, Geo-Ridge berm,


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coir (coconut fiber) rolls or "logs," or other similar product..
Check dams should NOT be built in streams or guts.. "
They block normal streamflow, altering drainage patterns, and
can lead to channel bypass and dramatically increased erosion.


What to Consider


Check dams should be used only in small open channels that .' .. -.
will not be overtopped by flow once the dams are built. The Figure 3.24. Installation of a triangular dike as a check
dam in a drainage swale (Estate St. George's Hill, St.
maximum drainage area above the check dam should not be in 1998 sale Ese St Gerge H St
larger than two (2) acres. The center section of the
check dam should be lower than the edges, and I V"2* ,EPEMtI,
00 CHN*JEL SLOWE
should not be higher than two (2) feet. Check dam A
side slopes should be 2:1 or flatter. Dams should 1 -~ --," ""..I a .,r
be spaced so that the toe of the upstream dam is at "T -TER
the same elevation as the top of the downstream A-f
dam (Figure 3.24). -0.,OC

After each significant rainfall, check dams should "
be inspected for sediment and debris ""
accumulation. Sediment should be removed when A rIoN= ,-
it reaches one half the original dam height. Check /6 "
for erosion at edges and repair promptly. After
construction is complete, all stone and rip-rap FILTER FABIRICM r
should be removed if vegetative erosion controls sT1aN a-"
will be used for permanent stabilization. It is ....*t ...
important to know expected erosion rates and Figure 3.25. Check dam design example (Empire State Chapter, Soil and
important to know expected erosion rates and Water Conservation Society, 1997).
runoff flow rate for the swale or channel in which
this practice is to be installed. Contact DPNR's Division of Environmental Protection, USDA Natural Resources
Conservation Service, the UVI Cooperative Extension Service, or a licensed engineer for assistance in designing
this practice.

ADVANTAGES OF CHECK DAMS
Are inexpensive and easy to install.
May be used permanently if designed properly.
Allow a high proportion of sediment in stormwater runoff to settle out.
Reduce velocity and may provide water aeration.
May be used where it is not possible to divert runoff flow or otherwise stabilize the channel.
DISADVANTAGES OF CHECK DAMS
May kill grass linings in channels if the water level remains high after it rains or if there is significant
sedimentation.
Can reduce the hydraulic capacity of the channel.
May create turbulence that can erode channel banks.


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3-26











Sediment Traps


A sediment trap is built by excavating a pond or by installing an
earthen embankment across a low area or drainage swale. An
outlet or spillway from the trap is built using large stones or
aggregate to slow the release of stormwater runoff. Sediment
traps are designed to retain runoff long enough to allow most
of the sediment to settle out. There are six basic types of
sediment traps: pipe outlet traps, grass outlet traps, storm inlet
traps, swale traps, stone outlet traps, and rip-rap outlet traps.


When and Where to Use Sediment Traps


A temporary sediment trap should be used in conjunction with
other temporary practices, such as gravel construction
entrances, temporary seeding, silt fences, and diversion dikes,


swales, or channels. Sediment traps are
drainage areas and should be installed at
stormwater discharge points from a
disturbed area. Pipe, stone and grass
outlet sediment traps can handle
maximum drainage areas of 5 acres or
less; storm inlet traps can handle 3 acres
or less; swale traps can handle 2 acres or
less; and rip-rap outlet traps can handle
10-15 acres. Sediment traps should NOT
be installed in guts or used to artificially
break up a natural drainage area into
smaller sections where a larger device
(sediment basin) would be more
appropriate. Figures 3.26 to 3.29 show
the different types of outlets that can be
used with sediment traps. Larger drainage
areas require larger sediment traps, and
larger traps require more detailed
engineering design.

F
What to Consider


suitable for small


YARD DRAIN
As required


1:1 orflatter I 1:1 orflatter


CROSS SECTION
Figure 3.26. Storm inlet sediment trap design (Empire
State Soil and Water Conservation Society, 1991).


Top of compacted embankment
min. 1' above top of stone Top of embankment or
lining. Max. 4' above existing ground
existing ground. m L 7 a2:1 Stone thickness 18" min.
max. 2:1
^sidpe 4" -12" stone or SHA class I.
Botom width of weir filter cloth
|(b) min. dept of channel (a)
CROSS SECTION
*NOTE: max. drainage area= 10 acres
4' min. width
Storage height 4'max.. .----Apron length 10'
limit min..
Excavate for wet storage -
as required st Filter cloth shall be embedded at ..
least 6" into the existing ground at Trap discharge
entrance to the outlet channel. to undisturbed/
stabilized area.
PROFILE



Compacted Positive
Embankment

Channel side formed by
compacted embankment or
Flare apron equal excavation into existing ground.
Flare apron equal to 1.5 times
the weir width (b) at ending point.
PERSPECTIVE VIEW
figure 3.27. Rip-rap outlet sediment trap example (Maryland Department of the
Environment, 1994).


The sediment trap should be large enough to allow soil particles to settle out of stormwater and should have
enough capacity to store collected sediment until it is removed. The volume of sediment storage that the
sediment trap provides depends upon the amount and intensity of expected rainfall and on estimated quantities
of sediment in stormwater runoff. However, storage capacity should allow for an average of 3600 cubic feet per
acre of drainage area contributing stormwater to the trap. This sizing is used in areas where the soils have high
clay contents in order to allow for greater settling of fine particles. Due to the predominance of clayey soils in


Environmental Protection Handbook 3-27


Chapter 3


Erosion and Sediment Control Practices


' *- '*








Chpe rso n edmn oto rcie


the Virgin Islands, sizing basins to 3600 ft3 per
acre of drainage area will allow for greater
sediment removal through longer retention of
sediment-laden stormwater. However, larger
sediment traps need more detailed engineering
design and may not be practical for small sites.


Sediment traps should be installed prior to
grading or filling, and they must be located at least
20 feet away from an existing building foundation.
Sediment trap embankment height should not
exceed 5 feet and should have a minimum 4 foot
wide top and side slopes of 2:1 or flatter. The trap
embankment should be compacted during
construction. The sediment trap outlet should be
designed so that sediment does not leave the trap
and so that erosion at or below the outlet does not
occur. Sediment traps must outlet water onto
stabilized (preferably undisturbed) ground, or into
a stabilized channel, drainage, or storm drain
system (Maryland Department of the
Environment, 1994). Contact DPNR's Division of
Environmental Protection, USDA Natural
Resources Conservation Service, the UVI
Cooperative Extension Service, or a licensed
engineer for assistance in designing this practice.


DIKE



MU5T REMAIN UNDISTURBED.
LEVEL. WELL VEEETATEDO .




DIKE IF REQUIRE TO DIVERT wATER TO TRAP
OUEJFL(: f F CLEANER WATER
UTFLCW OF CLEANER WATER INFLOW OF SEDIMENT LAOEN WATER



CRqET TVITH FT -4xCRAINAGE AREA ACRES
SECTION A-A
EXCAVATED GRASS OUTLET SEDIMENT TRAP



LEVEL BOTTOM INTO
UPHILL GRADIENT
T


SECTION A-A

SWALE SEDIMENT TRAP

EBHDULDEA
I NE T- t1 A
(MEDIAN) TRP SIZE DEPENDS DN
7 EDUJ.RE ETP.AN..
aWALE SEDIMENT TRAP RE| RED STORE.
SHOULDER
A TI RMTAj i i -i 0 OR COVERED WITHr
G 6 L i'l7C :-. BTONE
Figure 3.28. Grass outlet and swale outlet sediment trap designs (Empire
State Chapter, Soil and Water Conservation Society, 1997).


The effective life of a sediment trap depends on proper maintenance. The trap should be easily
accessible for regular maintenance and sediment removal. Traps should be inspected after each rainfall and
cleaned when one-third (1/3) to one-half (V) the design volume has been filled with sediment. The trap should
continue to be used and maintained until the site is permanently stabilized by vegetation and other permanent
practices. After completion of construction and site stabilization, all sediment traps should be removed and the
trap areas should be graded and vegetatively stabilized.


ADVANTAGES OF SEDIMENT TRAPS
Protect downstream areas from sedimentation.

Are relatively inexpensive and easy to install.

Are suitable for individual home sites or smaller developments (up to 10 acres, depending upon the type of
sediment trap (see Appendix B).
DISADVANTAGES OF SEDIMENT TRAPS
SAre not suitable for large developments or steep slopes.

SAre only effective if properly maintained.

Will not remove very fine silts and clays from stormwater runoff.

Must be removed after construction and stabilization are completed, unless converted to a permanent
retention basin (see Chapter 4).


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Chapter 3 Erosion and Sediment Control Practices


1/2" hardware cloth (wire) with filter
cloth securely fastened to
perforated riser



Compacted earth
embankment


FLOW


Excavate as
necessary for
storage


Outlet protection


PERSPECTIVE VIEW


Rip-rap protection



18" minimum
thickness of
4"- 12" stone


4' max. height
(fill)

BOTTOM
BOTTOM


Geotextile class C


FLOW

\


Existing ground


SECTION B-B


Crest
elevation PE
S1
. r12" minimum


SDischarge to
undisturbed/stabilized
area

PERSPECTIVE VIEW


0,_ / ",-Geotextile
Class C
Excavated for Small rip-rap 4" 7"
required wet
storage SECTION A-A
Bottom elevation


- Outlet elevation
apron (see note)

NOTE: 5' minimum length up to 5
acres. Over 5 acres use stone/
riprap sediment trap ST-IV.


Figure 3.29. Examples of pipe and stone outlet sediment traps (Maryland Department of the Environment, 1994).


Environmental Protection Handbook 3-29


1'min.

Existing
ground


Chapter 3


Erosion and Sediment Control Practices










Temporary Sediment Basin


A temporary sediment basin is a settling pond with a controlled stormwater release structure used to collect and
store sediment produced by construction activities. A sediment basin can be constructed by excavation and/or
by placing an earthen embankment across a low area or drainage swale or channel. Sediment basins can be
designed to maintain a permanent pool or to drain completely dry. The basin detains sediment-laden runoff from
larger drainage areas long enough to allow most of the sediment to settle out.

The pond has a riser and pipe outlet with a gravel outlet or spillway to slow the release of runoff and provide
some sediment filtration. By removing sediment, the basin helps prevent clogging of offsite conveyance systems
and sediment-loading of receiving waters.


When and Where to Use Temporary Sediment Basins


Temporary sediment basins are usually designed for disturbed areas larger than 5 acres. A sediment basin should
be installed before clearing and grading is undertaken. It should NOT be built in a stream or gut. The creation
of a dam at these sites may result in destruction of aquatic and moist forest habitats and flooding may result from
dam failure. A temporary sediment basin should only be used at sites where there is sufficient space and
appropriate topography. A temporary sediment basin used in combination with other control practices such as
temporary seeding, diversion dikes and swales, drainage swales, and/or mulching and matting is especially
effective in removing sediment.


What to Consider


The pond area in a temporary sediment basin should be large enough to hold runoff long enough for sediment
to settle out. Sufficient space should be allowed for collected sediments. Sediment trapping efficiency is improved
by providing the maximum surface area
possible. Because finer silts and clays may not Control section
settle out completely, additional erosion Emergency spillway
should not be
control measures should be used to minimize constructed
overfill
release of fine silt. Runoff should enter the material.
basin as far from the outlet as possible to Pmno
provide maximum retention time (i.e., the
flow path, or length of flow in the sediment
basin should be maximized. Appendix B has
detailed specifications and criteria to follow in
designing a sediment basin to fit each specific
site. Figure 3.30 depicts a sample sediment
basin design. Minimum storage
volume

The useful life of a sediment basin 7 .'// ewatenng
depends on regular maintenance. Sediment outlet
storage and- '
Sediment basins should be readily accessible permanent pool
for maintenance and sediment removal. They
should be inspected after each rainfall event Cross Section
and be cleaned out when about half the Figure 3.30. Temporary sediment basin design (U.S. EPA, 1992).


Chapter 3


Erosion and Sediment Control Practices


Environmen tal Protection Handbook


3-30









volume has been filled with sediment. The basin should remain in operation and be properly maintained until
the construction site is permanently stabilized by vegetation. If the basin is located near a residential area, it is
recommended for safety reasons that a sign be posted (child hazard, no playing) and that the area be secured by
a fence. A well-built temporary sediment basin that is large enough to handle post-construction runoff volume
may later be converted to use as a permanent stormwater management structure (see Chapter 4).

The outlet pipe and spillway of the sediment basin should be designed by an engineer based upon an analysis of
the expected runoff flow rates from the site. Contact DPNR's Division of Environmental Protection, USDA
Natural Resources Conservation Service, the UVI Cooperative Extension Service, or a licensed engineer for
assistance in designing this practice.


ADVANTAGES OF TEMPORARY SEDIMENT BASINS
Protects downstream areas from clogging or damage due to sediment deposits generated during
construction activities.
S Can trap smaller sediment particles than sediment traps due to longer detention time.
Can be converted to a permanent stormwater detention structure, once construction is complete.
DISADVANTAGES OF TEMPORARY SEDIMENT BASINS
S Requires regular maintenance and removal of accumulated sediment and debris.
Will not remove very fine silts and clays unless used in conjunction with other sediment and erosion control
practices.
Is more expensive than other methods of sediment removal and requires larger area for installation.
Requires careful adherence to safety practices since ponds may attract children.




Storm Drain Inlet Protection


Storm drain inlet protection consists of a permeable barrier placed
around any inlet or drain to filter sediment out of stormwater. This
practice prevents sediment from entering the storm drain inlet
structures and getting into the storm drain system. It also prevents
the silting-in of inlets, storm drainage systems, or receiving
channels. Inlet protection may be composed of gravel and stone
with a wire mesh filter, block and gravel, or geotextile (filter fabric).
There are four basic types of inlet protection recommended in the
V.I.: stone and block drop inlet protection, excavated drop inlet VDAM oSAVAAlABET E
GRATE 3 IS STANDARD DIAMETER
protection, curb drop inlet protection, and geotextile drop inlet STAN-AD A--M
protection (see Figures 3.32 and 3.33). Commercially manufactured RE
inlet inserts (Beaver DamTM, Silt Sack', etc., see Figure 3.31) that
LIFTING STRAPS
remove sediment and other pollutants from are also available, but ALLOW EASY MOVEMENT
STANDARD FABRIC IS A OF UNIT WITH GRATE
have not been tested in the V.I. WOVEN MONOFILAMENT VERFLOWGAP


When and Where to Use Inlet Protection -.-,E- I ILET

DESIGN CO,' i
TO ALL SHA: ; -
This practice should be used where the drainage area to an inlet is CONCRETE .. LOWPROFILE W
disturbed, it is not possible to temporarily divert the storm drain AND"CURBAPPA TY
outfall into a trapping device, for small drainage areas where storm Figure 3.31. Example installation and diagram for
drain inlets will be ready for use before final stabilization, where a Beaver DamTM storm drain inlet protection (Dandy
Products, Inc., 2001).
Environmental Protection Handbook 3-31


Chapter 3


Erosion and Sediment Control Practices








Chpe rso n edmn oto rcie


Figure 3.32. Examples of filter fabric drop inlet and curb drop
inlet storm drain protection (Empire State Chapter, Soil and
Water Conservation Society, 1997).


Figure 3.33. Examples of stone and block inlet and excavated drop
permanent storm drain structure is being constructed inlet storm drain protection (Empire State Chapter, Soil and Water
*Conservation Society, 1997).
onsite, or where watertight blocking of inlets is notConservation Society, 1997).
advisable. Straw bales are NOT recommended for this practice. It should NOT be used in place of sediment
trapping devices.


Geotextiles are used for inlet protection when stormwater flows are relatively small with low velocities (Figure
3.32). This practice cannot be used where inlets are paved because the filter fabric must be staked into the
ground. However, commercially manufactured inlet inserts (Beaver Dam ", Silt Sack ", etc., see Figure 3.31)
can be used over flat grates, for curb and gutter inlets, or median barrier inlets. Block and gravel filters can be
used where velocities are higher. Gravel and mesh filters can be used where flows are higher and subject to
disturbance by site traffic (Figure 3.33).


What to Consider



Storm drain inlet protection is not meant for use in drainage areas that are larger than one acre or for large,
concentrated stormwater flows. This practice should be installed before any soil disturbance takes place in the
drainage area. The type of material used will depend on site conditions and the size of the drainage area.


"DONUT" DETAIL

Excavated Drop Inlet


side slope?

weep holes
Excavated depth mi forde- l jjJ lll Gravel -supported by
', max. 2belowtop watering hardwarecloth to
of inlet iil' imll allow drainage and
MAIm restrict sediment
-II |- movement.
~iII HP-"ill


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Erosion and Sediment Control Practices


Environmen tal Protection Handbook


3-32









Inlet protection should be used in combination with other practices, such as small sediment traps, to provide
more effective sediment removal. Inlet protection structures should be inspected regularly, especially after a
rainstorm. Repairs and sediment removal should be performed as necessary. This practice should be removed
only after the disturbed areas are completely stabilized.

ADVANTAGES OF STORM DRAIN INLET PROTECTION
Effective in preventing clogging of existing storm drainage systems and reduces receiving water siltation.
Reduces the amount of sediment leaving the site.
DISADVANTAGES OF STORM DRAIN INLET PROTECTION
SMay be difficult to remove collected sediment.
SRequires regular maintenance and cleaning.
SMay cause erosion elsewhere if clogging occurs.
Is practical only for low sediment, low volume flows (disturbed areas 1 acre or less).



Outlet Protection


Outlet protection reduces the depth, speed and energy of Pipe Outlet to Flat Areas -
concentrated stormwater flows, reducing erosion and scouring at no well-defined channel
stormwater outlets of culverts, swale and drainage channels. Outlet
protection also reduces the potential for downstream erosion. This "
protection can be achieved through a number of methods including --J
stone or rip-rap, concrete aprons, paved sections, and settling basins-
installed below the storm drain outlet.
Plan

When and Where to Use Outlet Protection I -- La


Outlet protection should be installed at all pipe, interceptorection AA Filter
dike, swale, culvert or channel section outlets where the blanket
velocity of flow may cause erosion at the pipe outlet and in Pipe Outlet to Well-drained
the receiving channel. This practice applies to culvert outlets of Channel
all types; pipe conduits from all sediment basins, dry stormwater
ponds, and permanent ponds; and new channels built as outlets for
culverts or other drainage ways. Outlet protection should also be A
used at outlets where the velocity of flow at the design capacity may
result in plunge pools (small permanent pools located at the inlet to
or the outfall from control practices). Outlet protection should be Plan
installed early during construction activities, but may be added at
any time, as necessary.
La

What to Consider

I ie SectionAA
The exit speed of runoff as it leaves the outlet protection structure Filter
blanket
should be reduced to levels that minimize erosion. The design of Figure 3.34. Examples of rock outlet protection
outlet protection depends on the location. Pipe outlets at the top of designs (U.S. EPA, 1992).

Environmental Protection Handbook 3-33


Chapter 3


Erosion and Sediment Control Practices









cuts or on slopes steeper than 10 percent cannot be protected by rock aprons or rip-rap sections because re-
concentration of runoff flows and high velocities may occur after the flow leaves the apron. Contact DPNR's
Division of Environmental Protection, USDA Natural Resources Conservation Service, the UVI Cooperative
Extension Service, or a licensed engineer for assistance in designing for tailwater depth, apron size, bottom grade,
alignment, materials, thickness, stone quality, and filter for this practice. Appendix B contains design
specifications and example design procedure calculations (see example in Figure 3.34).

Once a rip-rap outlet has been installed, maintenance needs are usually low. Outlet protection should be
inspected on a regular schedule to look for erosion and scouring and to check if any stones have been dislodged.
Outlets must be kept clean of clogging debris. Repairs should be made promptly.


ADVANTAGES OF OUTLET PROTECTION
Provides, with riprap-lined apron (the most common outlet protection), a relatively low-cost method that can
be installed easily on most sites.
Removes sediment in addition to reducing runoff speed.
Can be used at most outlets where flow speed is high.
Is an inexpensive but effective practice.
S Requires less maintenance than many other practices.
DISADVANTAGES OF OUTLET PROTECTION
S May cause problems in removing collected sediment (without removing and replacing the outlet protection
structure itself).
May require frequent maintenance for rock outlets with high velocity flows.
May be unsightly.




Gabion Inflow Protection


Gabion inflow protection uses a temporary, lined drainage way installed to convey concentrated stormwater
runoff into sediment traps and basins in order to prevent erosion of the flow channel. Gabions are constructed
of rock or concrete within a flow channel to stabilize the channel. It should be used in conjunction with dikes,
swales or other water control devices as warranted by site conditions.


When and Where to Use Gabion Mattresses

1' min.
Gabion inflow protection should be used where Compacted embankment 1 Compacted
Embankment
stormwater runoff entering sediment basins or
traps will cause erosion of the embankments or / .
channels leading to them. Runoff can be directed 2:1 s
to the entrance of the gabion using dikes or sales. / Standard Sybol
/ TraplBasin Bottom S --I

What to Consider
PERSPECTIVE VIEW
STrap/basin bottom 'I
A gabion mattress should be constructed ofTralbasin botto
9'x3'x9' gabion baskets to form a cross-section oner c
PROFILE ALONG CENTERLINE
foot deep with 3:1 side slopes and a 3 foot bottom PROFILE ALONG CENTERLINE
width (see Figure 3.35). The top mattress should Figure 3.35. Gabion mattress inflow protection (Maryland Department of
the Environment, 1994).


Chapter 3


Erosion and Sediment Control Practices


Environmen tal Protection Handbook


3-34









be anchored into the ground at least one foot. Geotextile (or filter) fabric should be installed under all gabion
baskets. The fabric used should be the same as that used for swale channel stabilization (see Drainage Swale and
Silt Fence sections).

ADVANTAGES OF GABION INFLOW PROTECTION
Removes sediment in addition to reducing runoff speed.
Can be used at most inlets where flow speed is high.
S Requires less maintenance than many other practices.
DISADVANTAGES OF GABION INFLOW PROTECTION
S May cause problems in removing collected sediment (without removing and replacing the inlet protection
structure itself).
May require frequent maintenance for gabion inlets with high velocity flows.
May be expensive.



3.4 REFERENCES

CWP. 2000a. Stormwater Management Factsheet: Grassed Filter Strip, Center for Watershed Protection, Stormwater
Manager's Resource Center website www.stormwatercenter.net, Ellicott City, Maryland.

Dandy Products, Inc. 2001. Sediment Control Solutions for All Stormwater Systems and Dewatering Projects, Dandy
Products, Inc., Grove City, Ohio, website: www.dandyproducts.com.

DPNR-DEP and USDA-NRCS. 1998. Unified Watershed Assessment Report United States Vj, Islands, Virgin
Islands Department of Planning and Natural Resources in cooperation with USDA Natural Resources
Conservation Service, Caribbean Area, St. Croix, USVI.

Empire State Chapter, Soil and Water Conservation Society. 1997. New York Guidelines for Urban Erosion and
Sediment Control Update, Syracuse, New York.

Empire State Chapter, Soil and Water Conservation Society. 1991. New York Guidelines for Urban Erosion and
Sediment Control, Syracuse, New York.

Fifield, J.S. 1996. FieldManualfor FIT i,.- Sediment and Erosion Control Methods, HydroDynamics, Inc., Parker, CO.

MacDonald, L.H., D.M. Anderson and W.E. Dietrich. 1997. 'i .I -.. Threatened: Land Use and Erosion on
St. John, U.S. Virgin Islands," Environmental Management, Vol. 21, No. 6, pp. 851-863.

Maryland Department of the Environment, Water Management Administration. 1994. 1994 Maryland Standards
and \1'** m; -ii ,' for Soil Erosion and Sediment Control, Annapolis, Maryland.

Sampson, R. 1997. Precipitation, Runoff and Sediment Yield on St. John A Review of the Data, 319 Project Report to
Island Resources Foundation, February, 1997, St. Thomas, U.S. Virgin Islands.

Schueler, T.R. 1987. (.C....il.j Urban Runoff A Practical Manual for l.,iimj and Designing Urban BMPs,
Metropolitan Washington Council of Governments, Department of Environmental Programs, Washington, DC.
Publication Number 87703.



Environmental Protection Handbook 3-35


Chapter 3


Erosion and Sediment Control Practices









USDA-SCS. 1992. Engineering Field II. n,'I.....I, Chapter 18: Soil Bioengineeringfor Upland Slope Protection and Erosion
Reduction, U.S. Department of Agriculture Soil Conservation Service, Publication Number 210-EFH, 10/92,
Washington, DC.

USDA-SCS. 1993a. Conservation Choices: Yourguide to 30 conservation and environmental farming practices, USDA-SCS,
Des Moines, Iowa.

U.S. EPA. 1993. Guidance ;fil ',.i Management Measures for Sources of Nonpoint T'1..11 i. !-, in Coastal Waters. U.S.
Environmental Protection Agency, Office of Water, Publication Number 840-B-92-002, Washington, DC.

U.S. EPA. 1992. Storm Water Management for Construction Activities: Developing t'.1 ...-, Prevention Plans and Best
Management Practices. U.S. Environmental Protection Agency, Office ofWater, Document Number EPA 832-R-
92-005, Washington, DC.

Virgin Islands Department of Conservation and Cultural Affairs (DCCA). 1979. Environmental Laws and Regulations
of the V11,j, Islands, Title 12, Chapter 3, Trees and Vegetation Adjacent to Watercourses, 123 Cutting or Injuring Certain
Trees, Equity Publishing Corporation, Oxford, New Hampshire.

Washington State. 1992. Standards for Storm Water Management for the Puget Sound Basin. Washington State
Department of Ecology, Seattle, Washington.

Wernicke W., A. Seymour and R. Mangold. 1986. Sediment Study in the St. Thomas, St. Croix, Areas of the United
States Vlji, Islands. Donald E. Hamlin Consulting Engineers for the Virgin Islands Department of Conservation
and Cultural Affairs, Division of Natural Resources Management, St. Thomas, Virgin Islands.


3-36 Environmental Protection Handbook


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Environmen tal Protection Handbook


3-36







Chapter 4 Stormwater Runoff Control Practices

CHAPTER 4: STORMWATER RUNOFF CONTROL PRACTICES
TABLE OF CONTENTS



4.1 INTRODUCTION .................................................... 4-1

4.2 FILTRATION PRACTICES ............................................. 4-1

Buffer Zones ...................................... .................. 4-2
Grassed Swales ...................................... ................. 4-4
Sand Filters ...................................... ................... 4-5
W ater Q quality Inlets ................................................... 4-7

4.3 DETENTION PRACTICES .......................................... 4-8

Extended Detention Ponds .............................................. 4-8
Constructed W wetlands ................................................ 4-10

4.4 INFILTRATION PRACTICES .................................... 4-11

Porous Pavers ....................................................... 4-11
Infiltration Trenches ................................................. 4-12
Bio-R detention ...................................................... 4-15

4.5 REFERENCES ...................................................... 4-17


Environmental Protection Handbook 4-i









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4-il Environmental Protection Handbook


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Stormwa ter Runoff Con trol Practices


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CHAPTER 4: STORMWATER RUNOFF PRACTICES



4.1 INTRODUCTION

During development, both the landscape and the hydrology of a parcel of land can be significantly altered. The
following may occur both during and after development:

Soil porosity changes;
Impermeable surfaces increase;
Water retention on-site decreases;
Channels and other water conveyances are built;
Slopes change;
Vegetative cover decreases; and
Soil surface roughness decreases.

These changes result in increased runoffvolumes and velocities (or speeds) which can scour and erode guts, steep
slopes, and unvegetated areas, and cause downstream siltation of roads, parking lots, yards, ponds, beaches,
seagrass beds, coral reefs, and other coastal areas. In addition, impervious surfaces can also increase water
temperatures.

Stormwater management practices are designed to perform one or more of the following functions: decrease the
erosive potential of increased runoff volumes and velocities caused by land development; remove sediment and
other pollutants in stormwater runoff that result from activities that occur during and after development;
preserve or improve drainage patterns and other hydrologic conditions so that they closely resemble conditions
previous to development; and preserve natural systems. Stormwater control practices rely on three different
processes to treat runoff: filtration, detention, and infiltration.



4.2 FILTRATION PRACTICES

Examples of filtration practices that are suitable for conditions in the Virgin Islands include:

Buffer zones;
Grassed swales;
Sand filters; and
Water quality Inlets

Filtration practices treat sheet flow runoff by using vegetation or sand to filter and settle pollutants. In some
cases, infiltration and treatment of runoff in the subsoil may also occur. Some practices can also be installed in
storm drains to remove pollutants from water, particularly sediment, oil and grease. After being filtered, the
stormwater runoff can be routed into guts, drainage channels, or other waterbodies; evaporated; or infiltrated
into the surrounding soil. The microclimate of the area must be considered in selecting vegetative systems.


Environmental Protection Handbook 4-1


Chapter 4


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CHAPTER 4: STORMWATER RUNOFF PRACTICES



4.1 INTRODUCTION

During development, both the landscape and the hydrology of a parcel of land can be significantly altered. The
following may occur both during and after development:

Soil porosity changes;
Impermeable surfaces increase;
Water retention on-site decreases;
Channels and other water conveyances are built;
Slopes change;
Vegetative cover decreases; and
Soil surface roughness decreases.

These changes result in increased runoffvolumes and velocities (or speeds) which can scour and erode guts, steep
slopes, and unvegetated areas, and cause downstream siltation of roads, parking lots, yards, ponds, beaches,
seagrass beds, coral reefs, and other coastal areas. In addition, impervious surfaces can also increase water
temperatures.

Stormwater management practices are designed to perform one or more of the following functions: decrease the
erosive potential of increased runoff volumes and velocities caused by land development; remove sediment and
other pollutants in stormwater runoff that result from activities that occur during and after development;
preserve or improve drainage patterns and other hydrologic conditions so that they closely resemble conditions
previous to development; and preserve natural systems. Stormwater control practices rely on three different
processes to treat runoff: filtration, detention, and infiltration.



4.2 FILTRATION PRACTICES

Examples of filtration practices that are suitable for conditions in the Virgin Islands include:

Buffer zones;
Grassed swales;
Sand filters; and
Water quality Inlets

Filtration practices treat sheet flow runoff by using vegetation or sand to filter and settle pollutants. In some
cases, infiltration and treatment of runoff in the subsoil may also occur. Some practices can also be installed in
storm drains to remove pollutants from water, particularly sediment, oil and grease. After being filtered, the
stormwater runoff can be routed into guts, drainage channels, or other waterbodies; evaporated; or infiltrated
into the surrounding soil. The microclimate of the area must be considered in selecting vegetative systems.


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Buffer Zones


Buffer zones are areas of vegetated land along a shoreline, wetland or gut where development is prohibited.
Buffer zones are intended to physically protect and separate guts, wetlands and shorelines from development
activities. They also provide stormwater management, filter pollutants from stormwater runoff, provide food and
cover for wildlife and aquatic organisms, and provide cooling shade (CH2M Hill, 1998). There are three types
of buffer zones: setbacks, vegetated buffers and engineered buffers (CWP, 2001).

Setbacks are areas that separate waterways from potential pollution hazards (typically development sites).
Vegetated buffers are natural areas that exist to divide land uses or provide landscaping. Engineered buffers are
areas specifically designed to treat stormwater before it enters a gut, wetland or coastal area (CWP, 2001). They
may closely resemble natural ecosystems, such as grassy pastures or forests. Buffer zones are designed specifically
to protect waterbodies, slow stormwater runoff and remove pollutants from stormwater, and in this way differ
from Filter Strips (see Chapter 3), which are designed specifically to filter sediment from runoff.


When and Where to Use Buffer Zones


Forested buffers are well-suited to protect water quality and improve aquatic habitat in urban and suburban
landscapes. Buffer zones are generally used to protect guts, wetlands and/or shorelines from development activity,
to treat stormwater runoff from low density residential or resort developments, or to treat agricultural runoff.
One buffer zone design utilizes a three zone system with inner, middle and outer zones (Figure 4.1). Buffer zones
can increase infiltration and recharge to groundwater, slow stormwater runoff, reduce erosion of guts and
shorelines, improve and increase aquatic habitat, filter sediment, and remove soluble nitrogen and phosphorus
from stormwater (CH2M Hill, 1998).


What to Consider


Setbacks should have a minimum width of
100 feet to provide adequate protection of
waterbodies from development activities.
However, in urban and suburban areas where
open space is limited, narrower buffers
adjacent to guts and wetlands can still be
beneficial.

Effective buffer zone design (Figure 4.1) is
based on criteria that determine how a buffer
will be sized, delineated, managed and crossed
(see Appendix C).

For optimal stormwater treatment, buffers can
be designed with three lateral zones: a
stormwater depression leading to a grass filter
strip in turn leading to a forested buffer. The


The Three-Zone Buffer System


fBEg


S CcrL.pcl Pile





-> Z ZONE 3
"P-, P


N ul ZONE 1 f=1- ZONE 2


7U7 7 -7- Zn E ON 1 ZOE3U


'ro.Ent .wt.jiainsp i ">wj~d'it.r..ibfl. PrmlnEwrr a- f
I. i.Ofln lru pl. F wIT P 'I!r'cI InlS "

wirnIrdll INld ,..l atn..m *J, ..I r..t.. -
-t If P, 1 ,*
LrNi'Bi nmL r I MI I :. I *bI I : r
r. .. ....I.f1.. L 'h4g .I. :I. d Tfr. i
*g f1Ulo Jl tji -* t Ub *".ju I. lr lt"
**pmur* rmnf fi>-1MM b~C


Figure 4.1. Three-zone aquatic buffer system (CWP, 2001).


FUNCTION


iMDIH

TARGET

LL.OWLABLE
u5es


stormwater depression (or basin) captures and stores stormwater during smaller storm events. Larger stormflows


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are bypassed directly into a channel. The runoff captured in the depression can the be spread across a grass filter
strip (see Chapter 3). The grass filter then discharges into a wider forest buffer designed so that all the
stormwater is absorbed into the soil and not discharged to the water body (CWP, 2001).

Maintenance will be needed for any type of buffer zone. Buffer boundaries should be well-defined and visible
before, during and after construction. Buffers designed to capture and treat stormwater runoff from urban or
suburban areas will also need regular maintenance to prevent gullies from forming and bypassing the treatment.
Also, because buffer zones are maintained differently than park lawns, they may sometimes be seen as dangerous
or unkempt public places. Concerns may arise that the development of shrubby vegetation will interfere with
unimpeded views or be abused as dumping places for trash and litter. Therefore, an educational program
highlighting the environmental and recreational benefits of buffers should be a part of restoration programs
(CH2M Hill, 1998).


How Effective Are Buffer Zones?


Buffers lower runoff velocity, preserve natural vegetation around guts, wetlands and shorelines, stabilize banks
of drainage channels and guts, and slightly reduce both runoff volume and watershed imperviousness. In some
cases, buffers can also help to reduce the size and cost of downstream stormwater control facilities. The pollutant
removal effectiveness of buffer zones ranges widely and depends on the buffer type and design. Setbacks are
designed to prevent pollution from neighboring land uses, they are not designed for pollutant removal during
a storm (CWP, 2001).

Buffers, when designed correctly, can remove sediment, organic material, and many trace metals from
stormwater runoff. The rate of pollutant removal is thought to be a function of the length, slope and soil
permeability of the buffer, the size of the contributing runoff area, and the runoff velocity. Forested, or wooded,
buffers tend to remove a greater variety of pollutants than grassed filter strips, but since there is less vegetative
ground cover with forested buffers, they also need to be twice as wide as grassed buffers. Grass buffers are more
effective for trapping sediment, but forested buffers are more effective in reducing nutrient loads.

ADVANTAGES OF BUFFER ZONES
Relatively inexpensive to establish (cost almost nothing if preserved before the site is developed).
Can remove a high percentage of sediment and attached pollutants if designed properly.
Can provide privacy barrier, cooling shade, wind break, noise reduction, wildlife habitat, and protection of
guts, wetlands, shorelines and their vegetation.
Can protect increase infiltration, reducing flooding potential.
Maintenance tasks and costs are minimal for "natural" buffer strips.
Can provide recreational benefits.
DISADVANTAGES OF BUFFER ZONES
Potential loss of developable land.
Potential misuse of buffer zones as trash or litter dumps.
Potential increase in nuisance species (mosquitoes, mongoose. etc.)


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Grassed Swales


Grassed swales are shallow, vegetated, man-made ditches and channels designed to treat and infiltrate a
specified volume of stormwater runoff. The grass in the swale prevents erosion, filters sediment, and provides
some nutrient uptake. The underlying soil can also provide some filtering and treatment, absorb water, and
decrease stormwater volumes. Grassed swales can also be used to convey stormwater runoff. Enhanced grassed
swales, or biofilters, use check dams and wide depressions to increase runoff storage and promote settling of
pollutants.


When and Where to Use Grassed Swales


A grassed swale is an infiltration/filtration method that is usually used to provide pretreatment before
stormwater runoff is discharged to treatment systems or a water body. Swales are typically used in small
residential or commercial developments and are well suited to treat road or highway runoff, or as an alternative
to curb and gutter drainage systems. Swales are almost always used in combinationwith other stormwater control
or treatment practices.


What to Consider sl .

Grassed swales are not appropriate in arid a
areas where it is difficult to establish good
vegetative cover. Individual grassed swales
should be used to treat small drainage areas ...
(less than 5 acres). Grass swales are not
effective if they are built on slopes greater '
than 5% because stormwater velocity becomes
too great and causes erosion and prevents stonepr.ents
S c downstream scour
adequate infiltration or filtering. However, for Figure 4.2. Grassed swale design (Schueler, 1987).
steeper slopes (up to 15%), check dams (see
Chapter 3) can be installed to slow runoff and provide greater filtration and infiltration. Grassed swales should
also not be used in areas where groundwater is within two feet of the bottom of the swale.

Swale slopes need to be graded as close to zero as possible, and side-slopes should be no greater than 3:1 (Figure
4.2). The flat channel should be between two (2) and eight (8) feet wide. A dense cover of hardy, low-growing,
erosion-resistant grass or groundcover must be established (such as bermuda, bahia, hurricane or zoysia grass).
Swales should be mowed frequently during the wet season to stimulate grass growth, control weeds, and maintain
the system's capacity. Swales should never be mowed shorter than 4 inches. The soils underneath grassed swales
need to be very permeable (infiltration rate greater than 0.5 in/hr). Wood, rock or stone check dams can also
be installed in swales to promote infiltration, but earth or soil should not be used because moderate to severe
storms will blow out the dam.

Swale maintenance primarily involves keeping the grass cover dense. This requires periodic mowing, occasional
spot seeding, and weed control. Home owners are usually responsible for this maintenance. However, close
mowing and excessive fertilizer and pesticide applications can adversely affect swale performance and negate any
pollution reduction benefits the swale may have.


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How Effective Are Grassed Swales?


Grassed swales control peak stormwater runoff discharges by reducing runoff velocity and infiltrating a portion
of the stormwater runoff volume that passes through the swale. However, runoff infiltration is limited, and is
never more than 10% of total volume. Pollutants are removed by the filtering action of the grass, deposition into
low velocity areas, or infiltration into the subsoil. However, if a swale is constructed in soils having low
permeabilities, there will be no soluble pollutant removal and low to moderate sediment and other particulate
pollutant removal. Also, swales require relatively level slopes to function properly. The over-application of
fertilizers and pesticides by homeowners can make swales a source of pollutants, rather than a treatment
practice.

ADVANTAGES OF GRASSED SWALES
Are more economical to establish than curb and gutter drainage systems.
Have relatively low maintenance requirements.
Can protect surface infiltration trenches and storm drains from sediment clogging.
DISADVANTAGES OF GRASSED SWALES
Will not work on slopes greater than 5%.
Provide low to moderate particulate (sediment. etc.) removal and minimal soluble pollutant removal.



Sand Filters


A sand filter is usually a two-staged practice; the first stage is a chamber for settling sediment and other particles
in stormwater and the second is a sand-filled filter bed with a subsurface drain. Stormwater runoff is diverted
into the first chamber where large particles (sand, debris) settle out, and then flows to the second chamber where
small particles (clays) and some other pollutants (oil and grease, heavy metals) are filtered out. The stormwater
that seeps through the sand is collected in underground pipes and can then be reused for irrigation or returned
back to the drainage channel or gut. Enhanced sand filters use layers of peat, limestone, and/or topsoil, and
may also have a grass cover crop, to improve pollutant removal efficiency. Sand-trench systems have also been
developed to treat parking lot runoff.


When and Where to Use Sand Filters


Sand filters can be used on most development sites and have few constraining factors, but are best to use on small
sites (a maximum of 5 acres for surface sand filters or 2 acres for perimeter or underground filters). Sand filters
used for larger drainage areas often clog, necessitating sand replacement. Most sand filters have been used on
small parking lots. Sand filters are especially suitable for areas with thin clay soils, hilly terrain, high
evapotranspiration rates, low soil infiltration rates, limited space, and frequent droughts (Schueler, 1994). Most
sand filters have a contributing watershed area between a half an acre and ten acres, although the upper limit for
usage is 50 acres. Sand filters can also be used for retrofit purposes and in small developments in urban or
suburban areas. Figure 4.3 presents an example sand filter system.


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What to Consider STORWT SMET CHAMBER PLAN VIEW
I DETENTION BASIN SEMEN
ENERGY ISSFMTORS FILTRATION BASIN

/ -* MI MS l 41F- =-- ILT-ERED OUT-U "
Sand filters require relatively simple, but : Ti1E ;i;
frequent (quarterly), maintenance such as L uS
raking, surface sediment removal, and removal fI, STONE RIPRAP
& 'CHANNEL STONE RIPRAP
of trash, debris and leaf litter. Replacement of
the surface sand layer (top 2-3 inches) may.
also needed on a relatively frequent basis
(every 2 to 3 years). Sand filters are costly (up CROSS SECTION DIMENT ILTE
SEDIMENT B FILTERED OUTFLOW
to $10,000 to $20,000 per impervious acre CHeMBER
treated), but are long-lived and have lower UNDERDRAIN PIPNG SYSTE
maintenance and rehabilitation costs than Figure 4.3. Sand filter system (Austin, Texas, 1991).
infiltration trenches, and are more widely
applicable to environmental conditions in the Virgin Islands.

Sand filters need flow splitter designs that will not clog. Flow splitters are used to bypass larger flows to the storm
drain system or a stabilized channel. Sand filters also need adequate access and regular removal of surface
sediment to ensure longevity. They also require two to four feet of available head (the vertical drop between the
entrance and exit of a filter for gravity flow through the filter) for most off-line applications. The pretreatment
chamber should be able to hold at least 25% of the runoff volume to be treated in the practice. The sand filter
chamber should be able to hold at least 7 5% of the runoff volume to be treated in the practice. Typical runoff
volumes used are those from a 1" storm or 2" of runoff over the entire area draining to the practice. Sand filters
can be used in areas where groundwater quality is not a critical concern they should NOT be used in wellhead
protection areas unless treated water is routed to another practice for further treatment or removal. Cheaper
geotextiles or soil liners can also be used instead of concrete liners.


ADVANTAGES OF SAND FILTERS
S Excellent longevity and very few environmental limitations.
S Require little or no developable land (most are placed underground or on margins of parking lots).
Can be applied to most development sites and can be used in areas with thin soils and steeper slopes.
Have low maintenance/rehabilitation costs.
Are useful in watersheds where concerns over groundwater quality prevent the use of infiltration.
Have moderate to high pollutant removal capability.
DISADVANTAGES OF SAND FILTERS
Have frequent maintenance requirements.
Large, surface sand filters without grass covers may not be attractive in residential areas.
Some stormwater runoff will bypass filter during a large storm event.
Do not provide stormwater QUANTITY control.
High installation cost.


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Water Quality Inlets


Water quality inlets (also called oil-grit separators) are three-stage
underground structures designed to remove oil, grease, other
absorbed hydrocarbons, heavy sediment and other floating
substances from stormwater runoff before it is discharged to the
storm drain system and/or to guts, ponds or coastal waters (CH2M lfo \ itoragei
Hill, 1998). Other pre-fabricated products that perform a similar J camber
function are called storm drain or catch basin inserts. The many
different kinds and models available range from filter devices to
remove sediment to pre-fabricated oil-grit separators to multi-stage
treatment units that incorporate vegetation to help remove nutrients --
and other pollutants (Figure 4.4).


When and Where to Use Water Quality Inlets
Figure 4.4. Stormceptor@ operation during normal
flow conditions (Stormceptort Technical Manual,
Water quality inlets are used on sites that are expected to receive 1997).
heavy vehicular traffic or large amounts of petroleum. The inlets are
usually placed to catch the oil and fuel that leak from cars and trucks in parking lots, service stations, or loading
areas (Figure 4.5). The inlets can reduce maintenance of infiltration systems, detention basins, and other
stormwater devices and be used as a first stage of treatment by removing oil and sediment from stormwater
before it enters another larger stormwater pollution control practice, like a wet pond.

Water quality inlets can be installed in most areas for drainage areas no larger than 1 acre. They can be installed
in most any soil or terrain, and can be used near or at the impervious surface contributing the stormwater runoff.
Inlets need enough land area for the structure and to allow access for proper maintenance.


What to Consider


The pollutant removal efficiency of storm drain inserts
or water quality inlets varies depending on the volume
of the practice, flow velocity, and the depth of the
baffles and elbows in the chamber. These practices
should be inspected regularly and cleaned at least twice
a year to remove sediment, accumulated oil and grease,
floatables and other pollutants. The wastes removed
may be hazardous (such as petroleum products) and
may need to be disposed of with a licensed hazardous
waste hauler.


SIDE VEW
Access
Starmdrain hol




First chamber SI nd Cha mber Thi~


edImeimnt trapping) (Oil SeprniloQn) Chamber
U.-P



Figure 4.5. Schematic design of an oil-grit separator (Schueler, et
al., 1992).


ADVANTAGES OF WATER QUALITY INLETSIOIL-GRIT SEPARATORS
* Easily installed.
* Can effectively remove oily pollutants.
* Small inlets can be distributed over a large drainage area, instead of building a single large structure.
* Are not unsightly, because are hidden underground.


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DISADVANTAGES OF WATER QUALITY INLETSIOIL-GRIT SEPARATORS
Have frequent maintenance requirements.
Low removal of contaminants other than oil, grease and coarse sediment.
Difficult to maintain because of enclosed, underground design.
SSometimes odor is a problem.
Do not provide stormwater QUANTITY control.



4.3 DETENTION PRACTICES

Examples of detention practices that are suitable for conditions in the Virgin Islands include:

Extended detention ponds; and
Constructed wetlands

Detention practices temporarily hold runoff to control runoff rates and volumes, and to settle and retain
sediment and other pollutants. All detention practices use settling to remove particulate pollutants (sediment,
organic matter, etc.). Properly designed extended detention ponds can minimize erosion of downstream channels
by controlling water discharge speed. They can also remove nutrients and provide wildlife habitat if they are
landscaped and designed properly. Constructed wetlands and multiple-pond systems can further reduce
pollutants in runoff. Many of these systems are currently being designed to include vegetated buffer strips to
provide enhanced wildlife habitat and scenic areas.



Extended Detention Ponds


Extended Detention (ED) ponds temporarily hold a portion of stormwater runoff for up to 24 hours after
a storm, using a fixed outlet to regulate outflow at a specified rate. This allows sediment and other pollutants to
settle out of stormwater. ED ponds are usually "dry" between storms and do not have any permanent standing
water. They are typically made up of two stages: an upper stage that stays dry except for larger storms and a lower
stage that is designed to treat average storms. Temporary and most permanent ED ponds use a riser with an anti-
vortex trash rack (a type of trash screen that does not cause whirlpools to form in the pond or riser) on top to
control trash. Enhanced ED ponds also have a plunge pool near the inlet, a micropool at the outlet, and an
adjustable, reverse-sloped pipe as the ED control orifice (Figure 4.6).


When and Where to Use Extended Detention Ponds


Extended detention ponds can be implemented in most new developments, and can also be used to retrofit
existing dry ponds in older urbanized areas. They can be used on development sites 10 acres and greater. Soils
should neither be extremely impermeable (D soils) or extremely permeable (A soils). ED ponds can also be lined
with impermeable materials so that no infiltration occurs. The water collected can then be used to irrigate
gardens or lawns. The space required for ED ponds is usually less than 5% of the total site area.


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Maximum elevation of
What to Consider safet storm


Maximum
Runoff should be detained for at least 24 vati muofED '
hours to ensure sufficient pollutant pool' o
Sse we land retained I
removal. ED ponds should be designed, at forebay 7 ...
a minimum, to store the stormwater i "'"
runoff volume of a one-inch storm. safety 1 I
Different areas of the U.S. have developed aessto micro '' I
rules for sizing extended detention ponds
- these rules specify both a volume of
stormwater runoff to be detained and a
length of time over which the runoff is Figure 4.6. Dry extended detention (ED) pond design (Schueleretal., 1992).
released. Some sizing recommendations
include:

A volume equivalent to 2-inch of runoff distributed over the contributing watershed and released over
a 40-hour period;
Runoff volume generated from the one-year, 24-hour design storm and released over a minimum of 24
hours;
Runoff volume generated from the two-year, 24-hour design storm, released over 24 hours;
Runoff volume generated from a one-inch storm released over 24 hours; and
"First-flush" runoff volume (2-inch per impervious acre) released over 24 hours.

Two-stage ED ponds are most effective in removing pollutants. Slopes leading to the pond should be gentle
enough to prevent gully erosion of pond banks (i.e., side slopes no greater than 3:1 and banks no steeper than
2:1). If banks are steeper than 2:1 they should be stabilized with rip-rap to prevent erosion. The slope of the
upper stage of the ED pond should be between 2 and 5% to promote rapid drainage. The drainage channel
immediately below the pond outlet should be lined with large stone riprap and graded to a slope 0.5%. A layer
of filter cloth that conforms to the natural dimensions of the channel should be laid down and anchored with
18"-30" stone riprap.

ED ponds require routine maintenance including mowing, inspections, debris and litter removal, erosion control,
and nuisance control. Other maintenance that may be necessary includes structural repairs and equipment
replacement, and sediment removal.


How Effective Are ED Ponds?


Extending the detention time of dry ponds is an effective, low cost way to remove sediment from stormwater
runoff and to minimize downstream channel erosion. If stormwater can be detained for 24 hours or more, as
much as 90% of the particulate pollutants in stormwater runoff can be removed. However, ED ponds only
slightly reduce the levels of soluble nutrients in stormwater runoff, unless a shallow marsh is created in the wetter
portion of the pond. ED ponds can also significantly reduce the frequency of erosive downstream floods.


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ADVANTAGES OF ED PONDS
Significant pollutant removal, if designed properly.
Creation of local wetland and enhanced wildlife habitat.
Limited protection of downstream aquatic habitat.
S Only 10% more costly than conventional dry ponds.
DISADVANTAGES OF ED PONDS
Occasional nuisance problems (odor, debris, mosquitos, and weeds).
Moderate to high routine maintenance needs.
Eventual need for costly sediment removal and disposal.



Constructed Wetlands


Constructed wetlands are engineered systems designed to imitate natural wetlands ability to improve water
quality by treating and containing stormwater runoff and pollutants and decreasing pollutant loadings to coastal
waters. Constructed stormwater runoff wetlands simulate natural wetlands and attempt to replicate all of the
functions of natural wetlands.


When and Where to Use Constructed Wetlands


Wetlands can be constructed around the outside of a pond or in a sediment forebay (Figure 4.7).


What to Consider A max ED limit-
r 7' t o ,, '. Ir:r V i *
The most reliable method to create a 'l \ '
constructed wetland is to transplant live Lo y '
plants or dormant rhizomes from nursery I
stock. Transplantation from existing .
wetlands is not usually as effective and can '
be detrimental to the source wetland.
A \Pond buffer33' minimum
Most wetland species thrive in water less Figure 4.7. Example of a shallow marsh planting strategy (Schueler et al., 1992).
than one foot deep. To create these
depths over a wide area, sites usually need to be graded. Also potential sites must have enough baseflow
(subsurface water flow) or surface flow re-routing to ensure that severe seasonal evaporation does not damage
wetland vegetation. To achieve optimal pollutant removal, the surface area of the wetland should be the size of
about 2 to 3% of the total contributing watershed area.


How Effective Are Constructed Wetlands?


Establishing wetland species around new or existing wet ponds, dry ponds, or sediment basins is an effective, low
cost way to remove sediment and soluble pollutants from stormwater runoff, to minimize downstream channel
erosion, and to minimize stormwater runoff peaks. Constructed wetlands can also significantly reduce flooding
frequency downstream.


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ADVANTAGES OF CONSTRUCTED WETLANDS
* Significant pollutant removal, if designed properly.
* Creation of wildlife habitat and propagation of threatened or endangered wetland species.
* Limited protection of downstream aquatic habitat.
* Stabilizes pond or basin floors to prevent erosion.
* Vegetation costs are small portion of pond construction costs.
DISADVANTAGES OF CONSTRUCTED WETLANDS
* Difficulty in establishing native wetland vegetation.
* Engineering design assistance is limited.
* Need for steady water source.
* Increase of mosquitoes in stagnant areas.


4.4 INFILTRATION PRACTICES

Some infiltration practices that are appropriate for use in the Virgin Islands include:


Porous pavers;
Infiltration trenches; and
Bioretention areas.


Infiltration practices treat stormwater runoffby filtering it through the soil. Under natural conditions, water
percolates through the soil, where filtration and biological action remove pollutants. However, stormwater
treatment systems that use soil absorption require deep, permeable soils at separation distances of at least 4 feet
between the bottom of the structure and the groundwater. Long-term effectiveness of these practices depends
on proper operation and maintenance. Infiltration systems, some filtration devices, and sand filters should be
installed AFTER construction has been completed and the site has been permanently stabilized.

Infiltration and filtration systems that are clogged by sediment generated during construction
activities or because of premature use of these systems will fail.


Porous Pavers


There are two categories of porous paving or alternate pavers: paving blocks and
other surfaces including gravel, cobbles, brick or natural stone. Porous paving
materials are used in low-traffic areas (such as low-use parking lots, emergency
areas, driveways, walkways) in place of asphalt or concrete. Concrete tire-tracks
with grassed interiors can also be used for steeper driveways (Figure 4.8). Paving '
blocks can be concrete, cement or high-strength plastic grids placed on a
pervious base such as gravel or sand (Figure 4.9) The grids or pavers are then
filled with pervious materials such as sand, gravel or soil. Grids filled with soil can
be seeded to attain a grassed or lawn surface. The resulting system provides a
load-bearing surface that can to support vehicles while allowing infiltration of -
surface water into the underlying soil or bedrock (Figure 4.10). This reduces
stormwater runoff volume and discharge rate and improves water quality. figure 48. Porous driveway option
(Estate Lerkenlund, St. Thomas).


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When and Where to Use Porous Paving


Porous paving should only be used for lower volume parking 4 n p b
areas where heavy compaction will not be a problem, and is
most effective on sites with gentle slopes and moderate to
highly permeable soils.

Webbed cellular confinement systems work very well in
reducing erosion and stormwater runoff from gradual driveways Figure 4.9. Installation of interlocking plastic grid pavers
and low-use roads. For these uses, it is necessary for rock at UVI-CES Demonstration Garden, St. Thomas (photo
by Dale Morton, UVI-CES).
(gravel or crusher run) to be used as fill material instead of soil, b Dale Mrtn
in order to provide sufficient load support (especially if filter fabric is not placed below the webbing and fill
material).

Grassed block/grid cellular confinement systems can work well in controlling erosion and stormwater on fairly
level, low-use traffic areas, such as emergency access areas, driveways or parking lots. For higher or heavier used
parking areas, gravel fill would be more appropriate, as continual vehicular traffic damages the grass base. Some
disadvantages for use in the V.I. have been observed on the grassed demonstration system. First, the subsurface
must be completely level for the blocks to lay properly. Secondly, for a grassed parking area that requires soil fill,
the blocks should be filled by hand in order to avoid over-filling with soil. Over-filling reduces the blocks ability
to protect grasses planted within the system so that continual traffic will damage the sod.


How Effective is Porous Paving?


Porous paving can provide hydrologic conditions that
are similar to pre-development conditions. If installed
properly, this practice can control peak stormwater W'j^ 9,MV
discharges and can also reduce stormwater runoff .&'
volumes through infiltration. Porous paving materials .. a i -
are NOT intended to remove coarse sediment '-' W-" -
particles, but can provide significant pollutant removal ...
if the subsurface soil has adequate infiltration capacity. -
Stab nebn-r w'r
Because sediments can rapidly clog the base of the '
pavers, it is essential that practices (such as filter strips, ioi- 7,l 1
sediment traps, etc.) are used to keep coarse sediments
and other particles from entering the pavement Figure 4.10. Diagram of concrete grid pavers (Empire State
surface. The gravel or sand base beneath the papers Chapter, Soil and Water Conservation Society, 1997).
surface. The gravel or sand base beneath the pavers
may also be lined with filter fabric to prevent the rock material from becoming imbedded. Grassed porous pavers
should only be used for emergency or overflow parking areas because compaction caused by daily traffic flow will
kill grassed areas.


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ADVANTAGES OF POROUS PAVERS
Has load-bearing strength, longevity, and maintenance requirements similar to conventional pavement, when
properly installed.
Increases stormwater infiltration, decreases runoff volume, removes some pollutants, and preserves the
natural water balance at the site.
Reduces or eliminates the need for curbs and gutters in residential areas and for downstream conveyance
systems.
Provides a safer driving surface with better skid resistance and reduced hydroplaning.
DISADVANTAGES OF POROUS PAVERS
If it becomes clogged it is difficult and costly to repair. (The risk of premature clogging is high, and can only
be prevented if sediment is kept off the pavement before, during and after construction by filter strips,
sediment traps, etc.)
Not appropriate for high traffic areas.




Infiltration Trenches


Infiltration trenches are shallow, excavated ditches that have been backfilled with stone or gravel to form an
underground reservoir. Stormwater runoff is diverted into the trench and gradually infiltrates into the subsoil
and eventually into groundwater. Variations in infiltration trench design include enhanced infiltration trenches
(trenches that have extensive pretreatment systems to remove sediment and oil). Trench size depends on the
design storm volume of runoff to be controlled and the degree of infiltration (or infiltration rate) of the soil or
subsoil (Figure 4.11).


When and Where to Use Infiltration Trenches


Individual trenches are used primarily for on- Top View Sie View
site runoff control, and are rarely practical or D ..1'. ..
economical on sites larger than five acres. 8. ..... ldi"
Trenches are NOT designed to trap coarse .S'. __. -- .......e,
sediments. Runoff water should be pre- __ ...
treated (with filter or buffer strips or some ."
other kind of sediment trapping device) to I Z .. "
remove sediment and other particles to lower ..
trench failure rates. Trenches should be ....... ,I
placed on flat ground (5% slope or less), but
the slopes of the site draining to the practice ____
can be up to 15%. Trenches are not practical Figure 4.11. Parking lot perimeter trench design (Schueler, 1987).
for use in soils with infiltration rates less than
V inch/hour or more than 3 inches/hour, or with more than I' '.. clay or 40% silt/clay content (CWP, 1998).
Trenches should be located in areas with deep soils 2' to 5' of clearance from the bottom of the trench to
bedrock or water table is recommended (Schueler, 1992).


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What to Consider


Trenches have limited maintenance requirements aside from routine inspections and strict erosion and sediment
control. However, if a trench is allowed to clog, partial or complete replacement of the structure may be
required. Trenches have limited applications on steep slopes (> 15%).





Infiltration trenches can be located on the surface .
or below ground. Surface trenches may capture -
runoff directly from adjacent land areas, after it
has been filtered through a buffer (Figure 4.12).







trench.
Undergroundface trenches are used for more
rconcentrated runoff (from pipes, channels or
storm drains). However, special inlets need to be




installed in undthe smalleramound trenches to prevent
Figure 4.12. Graveled infiltration areas in a parking lot, St. Croix (photo
coarse sediment, oil and grease from clogging the by Dale Morton, UVI-CES).
trench.

Surface trenches are Top View
recommended for residential -_. .... _"
areas, where the smaller amounts
of sediment and oil that are R e.I l*l'o CK-Oarp z'
present can be trapped by grass fo*=
filters (Figure 4.13). Because the .
surface is exposed, these '"'
trenches have a slightly higher ;i .| "\ '-,
risk of clogging than
underground trenches, but they _. _
are also easier to maintain and
inspect. Underground
trenches are best suited for
Side View
larger developments (10 acres or
greater) where concentrated |lf
runoff from pipes or channels is ^ i :_ef. aoo.. ,,-, Roa
Should be Lems Thn Z%
directed to the trench. However, "
the runoff needs to be pre- so. a "'",'"'t, F et.. "
treated before entering the
trench, and it also needs to be Ii .a- n'"" Ly""
evenly distributed within the Efttr.tion
trench. Underground trenches Figure 4.13. Swale/trench design for a development (Schueler, 1987).
are also more difficult and costly to maintain.


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How effective are infiltration trenches?


Infiltration trenches can potentially reduce stormwater runoff so that hydrologic conditions are close to pre-
development conditions. Trenches designed to infiltrate all incoming water into the surrounding soil can
effectively reduce peak discharge rates associated with the design storm (the size of storm a given practice is
designed to handle). However, for both physical and economic reasons, it is not always practical to design
trenches for very large or infrequent storms. In this case, trenches that are designed to infiltrate part of the runoff
into the surrounding soil and collect the rest in a perforated underdrain at the bottom of the trench and direct
it to a central outlet, are more appropriate. Trenches can also reduce the increases in post-development runoff
volume that are produced by small or medium-sized storms. The effectiveness of a trench in reducing stormwater
runoff volumes is a function of the amount of water that can be infiltrated into the surrounding soil profile.

Infiltration trenches are not intended to remove sediment. They are designed to remove fine particles and soluble
pollutants by filtration through the trench and surrounding soil profile. Pollutant removal in a trench can be
enhanced by increasing the surface area of the trench bottom (i.e., make the trench shallow and broad rather
than narrow and deep). This will provide more area to increase infiltration into the surrounding soil profile and
provides more soil below the trench to further filter water. The greatest reduction of nutrients, metals, and
bacteria will occur in soils that have higher clay contents and/or organic matter, and the least reduction will occur
in sandy soils. Unfortunately, soils that maximize pollutant absorption also tend to have very low infiltration
rates. However, these soils are most prone to blockage, so it is vital that large particles are removed from
stormwater runoff (by a filter strip or other practice) before it enters the trench area.

The trench should be designed to completely drain within three days after the maximum design storm event.
Ifa trench is constructed over soils with a lower infiltration capacity, it may be advisable to adjust the depth of
the trench so that it drains in two days or less, as a safety margin. However, if a trench drains in less than 6 hours,
it will not provide adequate pollutant removal.

Test wells should be installed in every trench to monitor draining times after installation. The water level in the
well should be measured daily after a large storm. If the trench does not completely drain after 3 days it usually
means that the bottom of the trench is clogged and needs to be cleaned out. Otherwise, if a partial exfiltration
trench empties completely within one day, it means that either the underdrain is too large or that the bottom
of the trench has clogged, or both.


ADVANTAGES OF INFILTRATION TRENCHES
Preserve natural groundwater recharge capabilities.
Are relatively easy to fit into margins, perimeters and other un-utilized areas of a parking lot or development
site.
Are one of the few BMPs that provide pollutant removal on small sites or developments wedged in between
existing developments.
DISADVANTAGES OF INFILTRATION TRENCHES
Difficulties in keeping sediment out of the structure during site construction (especially if construction occurs
in phases).
The need for careful construction of the trench and regular maintenance.
Possible risk of groundwater contamination if toxic materials are introduced.
Require relatively flat area for the trench, 2 to 5 feet of soil profile, and well-drained soils.


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Bio-Retention



Bioretention systems are landscaped areas made of soil and sand mixtures and planted with native plants that
are used to filter stormwater runoff on residential and non-residential sites (CH2M Hill, 1998). They are usually
located in parking lot islands or within small pockets in residential land uses. Systems can be inline, located in
grasses swales modified to enhance pollutant removal (Figure 4.14), but are more commonly located offline. In
offline systems, surface runoff is directed into shallow, landscaped depressions. These depressions are designed
to mimic many of the pollutant removal mechanisms that operate in forested ecosystems. During storms, runoff
ponds above the soil and mulch, filtering through to the subsoil or to a perforated underdrain returning to the
storm drain system (Figure 4.15, next page). Runoff from larger storms bypasses the system directly into the
storm drain system.


When and Where to Use Bioretention


Bioretention is used on small sites (less than 5 acres) with flat slopes (5% or less), typically parking lots or small
residential areas, and for small storm events (1- to 5-year, 24-hour storm). It can be used in almost any soil
because the soil is made and placed in the system. Bioretention systems should be separated from the water table
by at least 3 feet.


What to Consider MAX.PONDED ,GROUNDCOVEROR
WATER DEPTH MULCH LAYER
SHEET FLOW (6 INCHES) /
Bioretention systems are most effective if C3----Z s
they are as close as possible to the sourcePLANTING S 4'MIN. 3
LIMIT 3:1 MAX.
of runoff. They have five basic features: PAVEMENT (TYPICAL)
pretreatment, treatment, conveyance, OPTIONALT GRAVEL BIPE
maintenance reduction and landscaping. 1' MIN SAND LBE- -N-SITU MATERIAL
Pretreatment practices like grassed filter BIORETENTION AREA
strips capture and remove coarse
Sr Figure 4.15. Off-line bioretention system design (CH2M Hill, 1998).
sediment from runoff water to reduce
maintenance and clogging of the system. Gabion Bire onPlants
A pea gravel level spreader (spreads flow i ieion Plts
evenly with no channels) can also be used. g.
S 1 Sand and Top

Treatment designs should size the ..--- 2'Sand
system between 5% and 10% of the Geowtile
impervious area draining to it, install a Figure 4.14. On-line bioretention cross section incorporated into a grass swale
sand/soil filter bed with a mulch layer with a mild to moderate slope (CH2M Hill, 1998).
above the soil bed, and allow runoff to pond 6" to 9" deep above the filter bed.

Stormwater should be conveyed to and from the practice to minimize erosion. Bioretention systems include
an underdrain system (perforated pipe in a gravel bed) that collects filtered runoff at the bottom of the filter bed
and channels it to the storm drain system. An overflow structure also needs to be designed to route flow from
large storms to the storm drain system. All parts of the system should be easily accessible for maintenance.


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