cvEPA
United
Enwronmental
for
for the
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Environmental Assessment for Proposed Effluent Guidelines
and Standards for the Construction and Development
Category
June 2002
United States Environmental Protection Agency
Office of Water (43 03 T)
1200 Pennsylvania Avenue, NW
Washington, DC 20460
^w^epa-goy/waterscjencg/guidg/
[EPA-821-R-02-009]
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Acknowledgments and Disclaimer
The Construction and Development Effluent Guidelines proposed rule and support documents
were prepared by the C&D Project Team: Eric Strassler, Project Manager; Jesse Pritts, P.E.,
Engineer; George Denning, Economist; Karen Maher, Environmental Assessor; and Michael G.
Lee, Attorney. Technical support for this Environmental Assessment was provided by Tetra
Tech, Inc.
Neither the United States government nor any of its employees, contractors, subcontractors or
other employees makes any warranty, expressed or implied, or assumes any legal liability or
responsibility for any third party's use of, or the results of such use of, any information,
apparatus, product or process discussed in this report, or represents that its use by such a third
party would not infringe on privately owned rights. Mention of trade names or commercial
products does not constitute endorsement by EPA or recommendation for use.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Contents
i
1.1 Introduction 1-1
1.2 Organization of Environmental Assessment 1-2
1.3 Review of Regulatory History to C&D 1-3
1.3.1 Clean Water Act 1-3
1.3.1.1 1-3
1.3.2 Other Local Government Storm Water Requirements 1-4
2
2.1 Introduction 2-1
2.2 Pollutants Associated with Construction Land Development
Water Runoff 2-2
2.2.1 2-2
2.2.1.1 Sources of Sediment 2-2
2.2.1.2 Receiving Waters 2-5
2.2.2 2-7
2.2.2.1 Runoff 2-8
2.2.2.2 Metals Impacts on Receiving Waters 2-10
2.2.3 and Oil and 2-11
2.2.3.1 Sources of PAHs, Oil and Grease 2-11
2.2.3.2 2-12
2.2.4 2-13
2.2.4.1 Sources of Pathogens 2-13
2.2.4.2 Receiving Water Impacts 2-15
2.3 Physical Impacts of Construction Land Development Activities 2-16
2.3.1 Hydrologic Impacts 2-18
2.3.1.1 Runoff Volume 2-19
2.3.1.2 Flood 2-22
2.3.1.3 Frequency Volume of Flows 2-22
2.3.1.4 Changes in Baseflow 2-22
2.3.2 on Geomorphology/Sediment Transport 2-23
2.3.2.1 Increased Transport of Sediment 2-23
2.3.2.2 Transport 2-25
2.3.2.3 Increase in Size of Channel 2-26
.3 in Structure 2-27
2.3.3.1 Embeddedness 2-27
2.3.3.2 2-28
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
2.3.3.3 In 2-29
2.3.4 Thermal 2-29
2.3.5 'Direct 2-30
2.3.5.1 Channel Straightening and Hardening/Reduction in
First Order 2-30
2.3.5.2 Fish 2-30
2.3.6 in Physical Impacts 2-30
3
3.1 Introduction 3-1
3.2 Methodology to Estimate Pollutant Loadings from Construction Runoff
Water Discharges 3-1
3.3 Characterizing the Nation's Stream Network 3-4
3.3.1 Characterizing the Stream Network within Developing Acreage 3-9
3.3.2 Characterizing the Flow Conditions in Stream Network 3-12
3.3.3 Converting Miles into Impact Estimates 3-14
4
4.1 Total Solids Loadings 4-1
4.2 Total Solid In-Stream Concentrations 4-3
4.3 Miscellaneous Impacts 4-4
5 5-1
Appendices
A. Evaluating Pollutant Loadings from Construction Activities Potentially Impact
the Environment A-l
B. Inventorying of Streams Potentially Impacted by Construction Activities B-l
C. Impacts of Construction Activity on Hydrology C-l
Tables
Table 1 -1. Regulatory Options Evaluated for Controlling Discharges from
Construction Activities 1-2
Table 2-1. Studies of Soil Erosion as TSS From Construction Sites 2-3
Table 2-2. Sources of in Urban 2-4
Table 2-3. Source Area Concentrations for TSS in Urban Areas 2-4
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Table 2-4. on Waters 2-6
Table 2-5. Metal Sources and Hot in Urban Areas 2-9
Table 2-6. Source Area Concentrations in Urban 2-10
Table 2-7. Metals Impacts on Receiving Waters 2-11
Table 2-8. Effects of PAHs Oil Grease on Receiving Waters 2-13
Table 2-9. Percentage Detection ofGiardia Cysts and Cryptosporidium Oocysts
in Wastewater Treatment Plant Effluent in the
New York City Water Supply Watersheds 2-15
Table 2-10. Effects of Bacteria on Waters 2-16
Table 2-11. Physical Impacts on Streams 2-17
Table 2-12. Hydrologic a Parking Lot a Meadow 2-20
Table 2-13. Comparison of Bulk Density for Undisturbed Soils and Common
Urban Conditions 2-21
Table 3-1. Common Construction Erosion and Sediment Control BMPs 3-2
Table 3-2. BMPs Evaluated by EPA for Effluent Guidelines 3-3
Table 3-3. Results of the National Survey 3-6
Table 3-4. Land Development Annually in 3-11
Table 3-5. Characterization of Stream Orders for Ecoregions 3-13
Table 3-6. Characterization of Length by Flow Type for Ecoregions 3-14
Table 3-7. Estimated Miles of Potentially Affected by One Year's
Construction 3-16
Table 3-8. Active Construction Site Runoff Scenarios for Option 1 Option 2 3-18
Table 3-9. Runoff Coefficients for Land Uses 3-18
Table 3-10. Runoff EMCs for Acres Within a 3-20
Table 4-1. Evaluated for Controlling from
Construction Activities 4-1
Table 4-2. Estimated TSS Loadings Reductions for Proposed Regulatory Options 4-2
Table 4-3. Development Scenarios Used to Estimate of Regulatory Options .... 4-3
Table 4-4. Estimated Average In-Stream TSS Concentrations Reduction 4-4
Figures
Figure 2-1.
Figure 2-2.
Figure 2-3.
Figure 2-4.
Figure 2-5.
Figure 2-6.
Figure 2-7.
Ultimate Channel
Altered Hydrograph in to Urbanization
Runoff Coefficient Versus Impervious Cover
Baseflow in to Urbanization: Nassau County, NY
Increased from an Urban Hydrograph
Sediment Production from Construction Sites
Network of Rock Creek, Maryland,
After Urbanization
2-18
2-19
2-20
2-23
2-24
2-25
2-26
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Figure 2-8. In Watts Branch, Maryland 2-27
Figure 2-9. Large Woody Debris as a Function of Watershed Impendousness 2-28
Figure 2-10. Temperature Increase In to Urbanization 2-29
Figure 3-1. Ecoregions for Stream Inventorying 3-5
Figure 3-2. Land Use Distribution of a Watershed 3-15
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Section 1 Introduction and Background
1.1 Introduction
The U.S. Environmental Protection Agency (EPA) is proposing national effluent limitation
guidelines for the construction and development (C&D) category. By establishing national
standards, EPA intends to reduce the environmental impacts of construction site storm water
discharges. This environmental assessment has been prepared to support the proposed rule by
identifying and estimating the environmental benefits of implementing the proposal.
For purposes of the environmental assessment, construction is defined as the process by which
land is converted from one land use to another. Hence, construction impacts are a result of how
the land is converted, not a result of what the land becomes.1 Land development is defined in this
document as the conversion of land from a pre-development condition such as rural land use to a
post-development condition such as urban land use. The impacts from the land development
industry originate from the post-development condition (what the land use becomes), which
causes adverse environmental effects that were not present in the pre-development condition.
Adverse environmental impacts attributable to the C&D industries have been well documented
and include (but are not limited to) alteration of stream flow patterns, change in river channels,
and reduction in the water quality of receiving waters as a result of increased generation and
transport of sediment. Aquatic habitats also can be damaged as a result of reduced water quality
and altered hydrology. These environmental impacts can in turn cause additional environmental
and economic damage by increasing the frequency and magnitude of flooding events in
vulnerable areas.
The purpose of this document is to describe the methods used to evaluate and quantify such
impacts as they occur under the current regulatory framework and might occur under the
proposed effluent guidelines. This report also presents estimates of the environmental benefits
that would accrue from implementation of the proposed technology controls. As discussed later
in the document, however, the environmental assessment and the associated Economic Analysis
of the proposed rule (EPA, 2002) only partially capture the full range of potential benefits that
would derive from implementing the proposed regulations. Not all categories of environmental
impacts from C&D activities can be quantified and therefore some are not amenable to
monetization procedures. These additional categories of environmental benefits are evaluated in
only a qualitative manner.
1. The term impact is used to denote negative conditions related to elevated concentrations of pollutants,
physical destruction or alteration of habitat by excessive flows, elevation of water temperature, and loss
offish spawning access due to new road crossings
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
The environmental assessment evaluates construction impacts for each of the three regulatory
options considered in the proposal. As shown in Table 1-1, these options range from no new
regulatory requirements (Option 3) to requirements for inspections and certifications of erosion
and sediment controls and implementation of new storm water pollution prevention plans for
certain sized sites.
Table 1-1. Regulatory Options Evaluated for Controlling Discharges
from Construction Activities
Option
Option 1
Option 2
Option 3
Description
Applicable to construction sites with one acre or more of disturbed land
Operators required to:
- Inspect site throughout land disturbance period
- Certify that the controls meet the regulatory design criteria as
applicable
Amend NPDES regulations at 40 CFR Part 122 (no new effluent
guideline regulations)
Applicable to construction sites with five acres or more of disturbed land
Operators required to:
- Prepare storm water pollution prevention plan
- Design, install, and maintain erosion and sediment controls
- Inspect site throughout land disturbance period
- Certify that the controls meet the regulatory design criteria as
applicable
Creates a new effluent guidelines category at 40 CFR Part 450 and
amends Part 122 regulations
No new regulatory requirements
The assessment, where appropriate, estimates reductions in environmental impacts attributable to
EPA's proposed rule. To help the reader understand the estimated changes under the regulatory
proposal, the document also summarizes the regulatory framework currently in place.
1.2 Organization of Environmental Assessment
This document first provides background information on the current regulatory framework and
summarizes how the proposed regulation would alter this framework. Section 2 provides
additional background information on how the C&D industries affect the environment through
generation of pollutants in storm water runoff and alteration of hydrology. A detailed discussion
of the methodology used to estimate environmental impacts from the C&D industries is provided
in Section 3. Section 4 presents EPA's estimates of environmental impacts of construction
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
activities under baseline conditions and under the various regulatory options evaluated for the
proposed rule. Section 5 provides the references used in the analysis. The appendices are
provided primarily for readers who seek further detail about how the methodology was
developed.
1.3 Review of Regulatory History Related to C&D Category
This subsection describes the federal and state regulations designed to control storm water
discharges from the C&D industries. It describes the regulatory framework that is currently in
place.
1.3.1 Clean Water Act
Congress adopted the Clean Water Act (CWA) to "restore and maintain the chemical, physical,
and biological integrity of the Nation's waters" (Section 101(a), 33 U.S.C. 1251(a)). To achieve
this goal, the CWA prohibits the discharge of pollutants into navigable waters except in
compliance with the statute. CWA section 402 requires "point source" discharges to obtain a
permit under the National Pollutant Discharge Elimination System (NPDES). These permits are
issued by EPA regional offices or authorized State agencies.
Following enactment of the Federal Water Pollution Control Amendments of 1972 (Public Law
92-500, October 18, 1972), EPA and the States issued NPDES permits to thousands of
dischargers, both industrial (e.g. manufacturing, energy and mining facilities) and municipal
(sewage treatment plants). In accordance with the Act, EPA promulgated effluent limitation
guidelines and standards for many industrial categories, and these requirements are incorporated
into the permits.
The Water Quality Act of 1987 (Public Law 100-4, February 4, 1987) amended the CWA. The
NPDES program was expanded by defining municipal and industrial storm water discharges as
point sources. Industrial storm water dischargers, municipal separate storm sewer systems and
other storm water dischargers designated by EPA must obtain NPDES permits pursuant to
section 402(p) (33 U.S.C. 1342(p)).
1.3.1.1 NPDE S Storm Water Permit Program
EPA's initial storm water regulations, promulgated in 1990, identified construction as one of
several types of industrial activity requiring an NPDES permit. These "Phase I" storm water
regulations require operators of large construction sites to apply for permits (40 CFR
122.26(b)(14)(x)). A large-site construction activity is one that:
will disturb five acres or greater; or
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
will disturb less than five acres but is part of a larger common plan of development or sale
whose total land disturbing activities total five acres or greater (or is designated by the
NPDES permitting authority); and
will discharge storm water runoff from the construction site through a municipal separate
storm sewer system (MS4) or otherwise to waters of the United States.
The Phase II storm water rule, promulgated in 1999, generally extends permit coverage to sites
one acre or greater (40 CFR 122.26(b)(15)).
In addition to requiring permits for construction site discharges, the NPDES regulations require
permits for certain MS4s. The local governments responsible for the MS4s must operate a storm
water management program. The local programs regulate a variety of business activities that
affect storm water runoff, including construction.
1.3.2 Other State and Local Government Storm Water Requirements
States and municipalities may have other requirements for flood control, erosion and sediment
(E&S) control, and in many cases, storm water quality. Many of these provisions were enacted
before the promulgation of the EPA Phase I storm water rule. All states have laws for E&S
control, and these are often implemented by MS4s. A summary of existing state and local
requirements is provided in the Development Document (EPA, 2002a). Key control measures
used by states and municipal/regional authorities in these programs include:
Storm water controls designed for peak discharge control
Storm water controls designed for water quality control
Storm water controls designed for flood control
Specified depths of runoff for water quality control
Percent reduction of loadings for water quality control (primarily solids and sediments)
Numeric effluent limits for water quality control (primarily total suspended sediments,
settleable solids, or turbidity)
Control measures for biological or habitat protection
Control measures for physical in-stream condition controls (primarily streambed and stream
bank erosion).
Control measures used to reduce pollutants entering water bodies are commonly required during
the construction (land disturbance) phase. Post-construction requirements for pollutant
reductions are generally broader and more stringent. Typically, water quantity control measures
for peak discharges and runoff volume controls that apply to post-development conditions are not
required during the construction phase.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Section 2 Categories of Reported Impacts and Pollutants
2.1 Introduction
Construction and land development activities can generate a broad range of environmental
impacts by introducing new sources of contamination and by altering the physical characteristics
of the affected land area. In particular, these activities can result in both short- and long-term
adverse impacts on surface water quality in streams, rivers, and lakes in the affected watershed
by increasing the loads of various pollutants in receiving water bodies, including sediments,
metals, organic compounds, pathogens, and nutrients. Groundwater also can be adversely
affected through diminished recharge capacity. Other potential impacts include the physical
alteration of existing streams and rivers due to the excessive flow and velocity of storm water
runoff.
Construction activities typically involve excavating and clearing existing vegetation. During the
construction period, the affected land is usually denuded and the soil compacted, leading to
increased storm water runoff and high rates of erosion. If the denuded and exposed areas contain
hazardous contaminants, they can be carried at increased rates to surrounding water bodies by
storm water runoff. Although the denuded construction site is only a temporary state (usually
lasting less than 6 months), the landscape is permanently altered even after the land has been
restored by replanting vegetation. For example, a completed construction site typically has a
greater proportion of impervious surface than the predevelopment site, leading to changes in the
volume and velocity of storm water runoff. Changes in land use might also lead to new sources
of pollution, such as oils and metals from motor vehicles, nutrients and pesticides from landscape
maintenance, and pathogens from improperly installed or failing septic tanks. Increased
pollutant loads are particularly evident when land development takes place in previously
undeveloped environments. Together the short-term impacts from construction activities and the
long-term impacts of development can profoundly change the environment.
The following subsections describe how pollutants associated with construction activities and
land development storm water discharges can adversely affect the environment. Potential effects
include impairment of water quality, destruction of aquatic life habitats, and enlargement of
flood plains. To the extent possible, this analysis distinguishes between environmental impacts
generated during construction and environmental impacts from post-development activities.
Although in most cases the differences are in magnitude and duration (e.g., sediment runoff),
environmental impairment from such contaminants as pathogens are more likely to be associated
with the overall urbanization of a watershed than with the types of activities that take place
during construction. The discussion of environmental impacts first evaluates the impacts of
contaminated runoff and then focuses on the physical impacts of construction and land
development.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
2.2 Pollutants Associated With Construction and Land Development Storm Water
Runoff
This subsection describes pollutants associated with construction and land development storm
water runoff. The description does not represent the complete suite of contaminants that can be
found in the runoff but focuses instead on those that are the most prevalent and of greatest
concern to the environment. These pollutants include sediment, metals, poly-aromatic
hydrocarbons (PAHs), oil, grease, and pathogens.
2.2.1 Sediment
Sediment is an important and ubiquitous constituent in urban storm water runoff. Surface runoff
and raindrops detach soil from the land surface, resulting in sediment transport into streams.
Sediment can be divided into three distinct subgroups: suspended solids, turbidity, and dissolved
solids.
Total suspended solids (TSS) are a measure of the suspended material in water. The
measurement of TSS in urban storm water allows for estimation of sediment transport, which can
have significant effects locally and in downstream receiving waters.
Turbidity is a function of the suspended solids and is a measure of the ability of light to penetrate
the water. Turbidity can exhibit control over biological functions, such as the ability of
submerged aquatic vegetation to receive light and the ability offish to breathe dissolved oxygen
through their gills.
Total dissolved solids are a measure of the dissolved constituents in water and are a primary
indication of the purity of drinking water.
2.2.1.1 Sources of Sediment
Construction Sites
Erosion from construction sites can be a significant source of sediment pollution to nearby
streams. A number of studies have shown high concentrations of TSS in runoff from
construction sites, and results from these studies are summarized in Table 2-1. One study,
conducted in 1986, calculated that construction sites are responsible for an estimated export of 80
million tons of sediment into receiving waters each year (Goldman, 1986, cited in CWP, 2000).
On a unit area basis, construction sites export sediment at 20 to 1,000 times the rate of other land
uses (CWP, 2000).
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-1. Studies of Soil Erosion as TSS From Construction Sites
Site
Seattle, Washington
SR204
Mercer Island
RT1
RT2
SB1
SB2
SB4
Pennsylvania Test Basin
Georgia Model
Maryland Model
Uncontrolled Construction Site Runoff
(MD)
Austin, Texas
Hamilton County, Ohio
Mean TSS (mg/L)
Mean Inflow
TSS
Concentration
(mg/L)
17,500
3,502
1,087
359
4,623
625
415
2,670
9,700
1,500 - 4,500
1,000 - 5,000
4,200
600
2,950
3,681
Source
Horner, Guerdy, and Kortenhoff, 1990
Horner, Guerdy, and Kortenhoff, 1990
Horner, Guerdy, and Kortenhoff, 1990
Schueler and Lugbill, 1990
Schueler and Lugbill, 1990
Schueler and Lugbill, 1990
Schueler and Lugbill, 1990
Schueler and Lugbill, 1990
Jarrett, 1996
Sturm and Kirby, 1991
Barfield and Clar, 1985
York and Herb, 1978
Dartiguenave, EC Lille, and Maidment,
1997
Islam, Taphorn, and Utrata-Halcomb, 1998
NA
Post-Development Conditions as a Source of Sediment
Sediment sources in urban environments include bank erosion, overland flow, runoff from
exposed soils, atmospheric deposition, and dust (Table 2-2). Streets and parking lots accumulate
dirt and grime from the wearing of the street surface, exhaust particulates, "blown-on" soil and
organic matter, and atmospheric deposition. Lawn runoff primarily contains soil and organic
matter. Source area monitoring data from Bannerman (1993), Waschbusch (2000), and Steuer
(1997) are shown in Table 2-3. Hot spots were identified for the transport of sediment from the
urban land surface, and they include streets, parking lots, and lawns.
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Table 2-2. Sources of Sediment in Urban Areas
Source Area
Bank erosion
Overland flow
Runoff from areas with exposed soils
Blown-on material and organic
matter
Loading
Up to 75 percent in California and Texas studies
Lawns - average value of geometric means from 4 studies: 201
mg/L
Average value: 3,640 mg/L
May account for as much as 35 to 50 percent in urban areas
Bannerman et al., 1993; Dartinguenave etal., 1997; Schueler, 1987; Steueretal., 1997; Trimble, 1997;
Waschbusch et al., 2000;
Table 2-3. Source Area Concentrations for TSS in Urban Areas
Source Area
Commercial parking lot
High-traffic street
Medium-traffic street
Low-traffic street
Commercial rooftop
Residential rooftop
Residential driveway
Residential lawn
TSS
(mg/L)a
110
226
305
175
24
36
157
262
TSS
(mg/L)b
58
232
326
662
15
27
173
397
TSS (mg/L)c
Monroe
Basin
51
65
51
68
18
15
59
Harper
Basin
69
17
34
122
"Steueretal., 1997.
b Bannerman etal., 1993.
c Waschbusch etal., 2000.
Parking lots and streets are responsible not only for high concentrations of sediment but also for
high runoff volumes. Normally about 90 percent of the water that falls on pavement is converted
to surface runoff, whereas roughly 5 to!5 percent of the water that falls on lawns is converted to
surface runoff (Schueler, 1987). The source load and management model (SLAMM; Pitt and
Voorhes, 1989) evaluates runoff volume and concentrations of pollutants from different urban
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
land uses and predicts loads to the stream. When used in the Wisconsin and Michigan
subwatersheds, the model estimated that parking lots and streets were responsible for more than
70 percent of the TSS delivered to the stream (Steuer, 1997; Waschbusch et al., 2000). Because
basin water quality measurements were taken at pipe outfalls, bank erosion was not accounted for
in the studies.
Sediment load is due to erosion caused by an increased magnitude and frequency of flows
brought on by urbanization (Allen and Narramore, 1985; Booth, 1990; Hammer, 1972; Leopold,
1968). Stream bank studies by Dartinguenave et al. (1997) and Trimble (1997) determined that
stream banks are large contributors of sediment in urban streams. Trimble (1997) used direct
measurements of stream cross sections, sediment aggradation, and suspended sediment to
determine that roughly 66.7 percent of the sediment load in San Diego Creek was a result of bank
erosion. Dartiguenave et al. (1997) used a GIS- based model developed in Austin, Texas, to
determine the effects of stream channel erosion on sediment loads. By effectively modeling the
pollutant loads on the land surface and by monitoring the actual in-stream loads at U. S.
Geological Survey (USGS) gauging stations, they were able to determine that over 75 percent of
the sediment load came from the stream banks.
2.2.1.2 Receiving Waters Impacts
Sediment transport and turbidity can affect habitat, water quality, temperature, and pollutant
transport, and can cause sedimentation in downstream receiving waters (Table 2-4). Suspended
sediment and its resulting turbidity can reduce light for submerged aquatic vegetation. In
addition, deposited sediment can cover and suffocate benthic organisms like clams and mussels,
cover habitat for substrate-oriented species in urban streams, and reduce storage in reservoirs.
Pollutants such as hydrocarbons and metals tend to bind to sediment and are transported with
storm flow (Crunkilton et al., 1996; Novotny and Chesters, 1989). Increased turbidity also can
cause stream warming by reflecting radiant energy (Kundell and Rasmussen, 1995).
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Table 2-4. Sediment Impacts on Receiving Waters
Resource
Affected
Streams
Wetlands
Reservoirs
Beaches
Impacts of Sediment
Loss of sensitive species and a decrease in
fish and macroinvertebrate diversity
communities
Clogging of gills and loss of habitat
Decreased flow capacity in streams
Interference with water quality processes.
Affects transport of contaminants
Deposition of sediment
Loss of sensitive species: amphibians,
plants
Turbidity results in increased costs of
treatment for drinking water
Sedimentation results in decreased storage
Turbidity reduces aesthetic value
Sedimentation can result in increased
accretion rates in wetlands and change
plant community structure
Indicator
GA loss of sensitive
species at 25 NTU
Maryland decreased
flow capacity. Increased
overbank flows
High accretion rates in a
tidal wetland as a result
of sediment transport in
an urbanized watershed
Loss of amphibian
species
Loss of seven
wetland/SAV plant
species since European
development
more abatement costs at
>5NTU
Source
Kundell and
Rasmussen, 1995
Leopold, 1973
Barrett and Molina,
1998
MacRae and Marsalek,
1992
Pasternack, 1998
Horner, 1996
Hilgartner, 1986
McCutcheon et al.,
1993
Kundell and
Rasmussen, 1995
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Table 2-4. Sediment Impacts on Receiving Waters
Resource
Affected
Estuaries
Impacts of Sediment
Sedimentation
Turbidity
Reduced light attenuation can lead to a loss
of submerged aquatic vegetation (S AV)
Indicator
SAV losses due to
sediments and
eutrophication
SAV losses in NE
Essential habitat
requirements for SAV
include light
attenuation, dissolved
inorganic nitrogen,
phosphorus and
chlorophyl-a
Loss of seven
wetland/SAV plant
species since European
settlement
Source
Pasternack, 1998
Livingston, 1996
Schiff, 1996
Mackiernanet al., 1996
Short and Wyllie-
Echeverria, 1996
Orth and Moore, 1983
Stevenson etal., 1993
Hilgartner, 1986
2.2.2 Metals
Many toxic metals can be found in urban storm water, although only metals such as zinc, copper,
lead, cadmium, and chromium are of concern because of their prevalence and potential for
environmental harm. These metals are generated by motor vehicle exhaust, the weathering of
buildings, the burning of fossil fuels, atmospheric deposition, and other common urban activities.
Metals can bioaccumulate in stream environments, resulting in plant growth inhibition and
adverse health effects on bottom-dwelling organisms (Masterson and Bannerman, 1995).
Generally the concentrations found in urban storm water are not high enough for acute toxicity
(Field and Pitt, 1990). Rather, it is the cumulative effect of the concentration of these metals
over time and the buildup in the sediment and animal tissue that are of greater concern.
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2.2.2.1 Sources of Metal Runoff
Construction Sites
Construction sites are not thought to be important sources of metal contamination. Runoff from
such sites could have high metals contents if the soil is already contaminated. Construction
activities alone do not result in metal contamination.
Post-Development Conditions as a Source of Metals
Post-development conditions create significant sources of metal runoff in the urban environment,
including streets, parking lots, and rooftops. Table 2-5 summarizes the major sources of metal
runoff by metal type. Copper can be found in high concentrations on urban streets as a result of
the wear of brake pads that contain copper. A study in Santa Clara, California, estimated that 50
percent of the copper released is from brake pads (Woodward-Clyde, 1992). Sources of lead
include atmospheric deposition and diesel fuel, which are found consistently on streets and
rooftops. Zinc in urban environments is a result of the wear of automobile tires (an estimated 60
percent of the total zinc in the Santa Clara study), paints, and the weathering of galvanized
gutters and downspouts. Source area concentrations estimated by researchers in Wisconsin and
Michigan are presented in Table 2-6. Actual concentrations vary considerably, and high-
concentration source areas vary from study to study. A study using SLAMM for an urban
watershed in Michigan estimated that most of the zinc, copper, and cadmium was a result of
runoff from urban parking lots, driveways, and residential streets (Steuer, 1997).
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-5. Metal Sources and Hot Spots in Urban Areas
Metal
Zinc
Copper
Lead
Cadmium
Chromium
Sources
Tires, fuel combustion, galvanized pipes and
gutters, road salts
Estimate of 60% from tires'"
Auto brake linings, pipes and fittings,
algacides, and electroplating
Estimate of 50% from brake pads*
Diesel fuel, paints, and stains
Component of motor oil; corrodes from alloys
and plated surfaces
Found in exterior paints; corrodes from alloys
and plated surfaces
Hot Spots
Parking lots, rooftops, and
streets
Parking lots, commercial
roofs, and streets
Parking lots, rooftops, and
streets
Parking lots, rooftops, and
streets
More frequently found in
industrial and commercial
runoff
a Woodward-Clyde, 1992 (Santa Clara, CA, study)
Sources: Barr, 1997; Bannermanetal., 1993; Steuer, 1997
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-6. Metal Source Area Concentrations in Urban Areas (in ug/L)
Source Area
Citation
Commercial
parking lot
High-traffic
street
Medium-
traffic street
Low-traffic
street
Commercial
rooftop
Residential
rooftop
Residential
driveway
Residential
lawn
Basin outlet
Diss.
Zinc
(a)
64
73
44
24
263
188
27
na
23
Total
Zinc
(b)
178
508
339
220
330
149
107
59
203
Diss.
Copper
(a)
10.7
11.2
7.3
7.5
17.8
6.6
11.8
na
7.0
Diss.
Copper
(b)
9
18
24
9
6
10
9
13
5
Total
Copper
(b)
15
46
56
24
9
15
17
13
16
Diss.
Lead
(a)
2.1
1.5
1.5
20
4.4
2.3
na
2.4
Diss.
Lead
(c)
1.7
1.9
0.5
Total
Lead
(a)
40
37
29
21
48
25
52
na
49
Total
Lead
(c)
25
46
10
Total
Lead
(b)
22
50
55
33
9
21
17
na
32
na: not available
Sources: (a) Steuer 1997;
(b) Bannerman 1993; (c) Waschbusch, 1996, cited in Steuer, 1997
2.2.2.2 Metals Impacts on Receiving Waters
Downstream effects of metal transported to receiving waters, such as lakes and estuaries, have
been studied extensively. Selected studies on metal impacts on receiving waters are summarized
in Table 2-7. Although evidence exists for the buildup of metals in deposited sediments in
receiving waters and for bioaccumulation in aquatic species (Bay et al., 2000; Livingston, 1996),
specific effects of these concentrations on submerged aquatic vegetation and other biota are not
well understood.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-7. Metals Impacts on Receiving Waters
Resource
Affected
Streams
Reservoirs/
Lakes
Estuaries
Impacts of Metals
Chronic toxicity due to in-stream concentrations
and accumulation in sediment
Bioaccumulation in aquatic species
Acute toxicity at certain concentrations
Accumulation of metals in sediment
Accumulation of metals in sediment
Loss of SAV
Evidence
Chronic toxicity increased during longer-
duration studies, i.e., 7/14/21-day studies
(Crunkilton, 1996);
Delayed toxicity (Ellis, 1986/1987);
Baseflow toxicity (Mederios, 1983);
Resuspension of metals during storms
accounting for some lexicological effects
(Heaney and Huber, 1978);
Bioaccumulation in crayfish (Masterson &
Bannerman, 1994)
Bioaccumulation levels in bottom-feeding
fish were found to be influenced by the metal
levels of the bottom sediments of storm water
ponds (Campbell, 1995).
Tampa Bay (Livingston, 1996);
San Diego (Schiff 1996);
SAV losses in northeast San Francisco Bay
(Orth and Moore, 1983)
2.2.3 PAHs, and Oil and Grease
Petroleum-based substances such as oil and grease and poly-aromatic hydrocarbons (PAHs) are
found frequently in urban storm water. Many constituents of PAHs and oil and grease, such as
pyrene and benzo[b]fluoranthene, are carcinogens and toxic to downstream biota (Menzie-Cura
and Assoc., 1995). Oil and grease and PAHs normally travel attached to sediment and organic
carbon. Downstream accumulation of these pollutants in the sediments of receiving waters such
as streams, lakes, and estuaries is of concern.
2.2.3.1 Sources of PAHs, and Oil and Grease
Construction Sites
Construction activities during site development are not believed to be major contributors of these
contaminants to storm water runoff. Improper operation and maintenance of construction
equipment at construction sites, as well as poor housekeeping practices (e.g., improper storage of
oil and gasoline products), could lead to leakage or spillage of products that contain
hydrocarbons, but these incidents would likely be small in magnitude and managed before off-
site contamination could occur.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Post-Development Conditions as a Source ofPAHs, and Oil and Grease
In most storm water runoff, concentrations of PAHs and oil and grease are typically below 5
mg/L but concentrations tend to increase in commercial and industrial areas. Hot spots for these
pollutants in the urban environment include gas stations, commuter parking lots, convenience
stores, residential parking areas, and streets (Schueler, 1994). Schueler and Shepp (1993) found
concentrations of pollutants in oil/grit separators in the Washington Metropolitan area and
determined that gas stations had significantly higher concentrations of hydrocarbons and a
greater presence of toxic compounds than streets and residential parking lots. A study of source
areas in an urban watershed in Michigan (which excluded gas stations) showed that high
concentrations from commercial parking lots contributed 64 percent of the estimated
hydrocarbon loads (Steuer et al., 1997).
2.2.3.2 Receiving Water Impacts
Toxicological effects from PAHs and oil and grease are assumed to be reduced by their
attachment to sediment (lessened availability) and by photodegradation (Schueler, 1994).
Evidence of possible impacts on the metabolic health of organisms exposed to PAHs and of
bioaccumulation in streams and other receiving waters does not exist (Masterson and
Bannerman, 1994; MacCoy and Black, 1998); however, crayfish from Lincoln Creek, analyzed
in the Masterson and Bannerman study, had a PAH concentration of 360 micrograms per
kilogrammuch higher than the concentration known to be carcinogenic. The crayfish in the
control stream did not have detectable levels of PAHs. Known effects of PAHs on receiving
waters are summarized in Table 2-8. Long-term effects of PAHs in sediments of receiving
waters call for additional study.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-8. Effects of PAHs and Oil and Grease on Receiving Waters
Resource
Affected
Streams
Reservoirs
Estuaries
Impacts of PAHs and Oil and Grease
Possible chronic toxicity due to in-stream
concentrations and accumulation in sediment
Bioaccumulation in aquatic species
Acute toxicity at certain concentrations
Accumulation of PAHs in sediment
Accumulation of PAHs in sediment
Potential loss of SAV
Accumulation of PAHs in fish and shellfish
tissue
Citations
Bioaccumulation in crayfish tissue studies
(Masterson and Bannerman, 1994);
Potential metabolic costs to organisms
(Crunkiltonetal., 1996);
delayed toxicity (Ellis, 1986/1987);
Baseflow toxicity (Mederios, 1983)
Sediment contamination may result in a
decrease in benthic diversity and transfer of
PAHs to fish tissue (Schueler, 2000-CWP);
Elevated levels of PAHs found in pond
muck layer (Gavens et al., 1982)
Tampa Bay (Livingston, 1996);
San Diego, San Francisco Bay (Schiff,
1996)
2.2.4 Pathogens
Microbes, or living organisms undetectable by the naked eye, are commonly found in urban
storm water. Although not all microbes are harmful, several species such as the pathogens
Cryptosporidium and Giardia can directly cause diseases in humans (pathogens). The presence
of bacteria such as fecal coliform bacteria, fecal streptococci, and Escherichia coli indicates a
potential health risk (indicators). High levels of these bacteria may result in beach closings,
restrictions on shellfish harvest, and increased treatment for drinking water to decrease the risk of
human health problems.
2.2.4.1 Sources of Pathogens
Construction Sites
Construction site activities are not believed to be major contributors to pathogen contamination
of surface waters. The only potential known source of pathogens from construction sites are
portable septic tanks used by construction workers. These systems, however, are typically self-
contained and are not connected to the land surface. Any leaks from them would likely be
identified and addressed quickly.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Post-Development Conditions as a Source of Pathogen Runoff
Coliform sources include pets, humans, and wild animals. Source areas in the urban
environment for direct runoff include lawns, driveways, and streets. Dogs have high
concentrations of coliform bacteria in their feces and have a tendency to defecate in close
proximity to impervious surfaces (Schueler, 1999). Many wildlife species also have been found
to contribute to high fecal concentrations. Essentially, any species that is present in significant
numbers in a watershed is a potential pathogen source. Source identification studies, using
methods such as DNA fingerprinting, have attributed high coliform levels to such species as rats
in urban areas, ducks and geese in storm water ponds, dogs, and even raccoons (Blankenship,
1996; Lim and Oliveri, 1982; Pitt et al., 1988; Samadapour and Checkowitz, 1998).
Indirect surface storm water runoff sources include leaking septic systems, illicit discharges,
sanitary sewer overflows (SSOs), and combined sewer overflows (CSOs). These sources have
the potential to deliver high concentrations of coliforms to receiving waters. Illicit connections
from businesses and homes to the storm drainage system can discharge sewage or washwater into
receiving waters. Leaking septic systems are estimated to constitute 10 to 40 percent of all
systems. Inspection is the best way to determine whether a system is failing (Schueler, 1999).
There is also evidence that these bacteria can survive and reproduce in stream sediments and in
storm sewers. During a storm event, they are resuspended and add to the in-stream bacteria load.
Source area studies reported that end-of-pipe concentrations were an order of magnitude higher
than any source area on the land surface; therefore, it is likely that the storm sewer system itself
acts as a source (Bannerman, 1993; Steuer et al., 1997). Resuspension of fecal coliform bacteria
from fine stream sediments during storm events has been reported in New Mexico (NMSWQB,
1999). The sediments in the storm sewer system and in streams may be significant contributors
to the fecal coliform load. This area of research certainly warrants more attention to determine
whether these sources can be quantified and remediated.
Giardia and Cryptosporidium in urban storm water are also a concern. There is evidence that
urban watersheds and storm events might have higher concentrations of Giardia and
Cryptosporidium than other surface waters (Stern, 1996). (See Table 2-9.) The primary sources
of these pathogens are humans and wildlife. Although Cryptosporidium is found in less than 50
percent of storm water samples, data suggest that high Cryptosporidium values may be a concern
for drinking water supplies. Both pathogens can cause serious gastrointestinal problems in
humans (Bagley et al., 1998).
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-9. Percentage Detection of Giardia Cysts and Cryptosporidium Oocysts in
Subwatersheds and Wastewater Treatment Plant Effluent in the New York City
Water Supply Watersheds
Source Water Sampled
(No. of sources/No, of samples)
Wastewater effluent (8/147)
Urban subwatershed (5/78)
Agricultural subwatershed (5/56)
Undisturbed subwatershed (5/73)
Percent Detection
Total
Giardia
41.5
41.0
30.4
26.0
Confirmed
Giardia
12.9
6.4
3.6
0.0
Total
Cryptosporidium
15.7
37.2
32.1
9.6
Confirmed
Cryptosporidium
5.4
3.9
3.6
1.4
Source: Stern etal., 1996.
2.2.4.2 Receiving Water Impacts
Fecal coliform bacteria, fecal streptococci, andE1. coli are consistently found in urban storm
water runoff. Their presence indicates that human or other animal waste is also present in the
water and that other harmful bacteria, viruses, or protozoans might be present as well.
Concentrations of these indicator organisms in urban storm water are highly variable even within
a given monitoring site. Data for fecal coliform bacteria illustrate this variability: site
concentrations range from 10 to 500,000 most probable number per 100 milliliters
(MPN/lOOmL) (Schueler, 1999).
Concentrations in urban storm water typically far exceed the 200 MPN/100 mL threshold set for
human contact recreation. The mean concentration of fecal coliform bacteria in urban storm
water for 34 studies across the United States was 15,038 MPN/lOOmL (Schueler, 1999).
Another national database of 1,600 samples (mostly Nationwide Urban Runoff Program data
collected in the 1980s), estimates the mean concentration at 20,000 MPN/100 mL (Pitt, 1998).
Fecal streptococci concentrations for 17 urban sites had a mean of 35,351 MPN/100 mL
(Schueler, 1999). Transport occurs primarily as a result of direct surface runoff, failing septic
systems, SSOs, CSOs, and illicit discharges.
Human health can be affected by bacterial impacts on receiving waters when bacteria standards
for water contact recreation, shellfish consumption, or drinking water are violated.
Epidemiological studies from Santa Monica Bay have documented frequent sickness in people
who swim near outfalls (SMBRP, 1996). Documented illnesses include fever, ear infections,
gastroenteritis, nausea, and flu-like symptoms. Table 2-10 describes the effects of bacteria and
protozoan problems on different receiving waters.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-10. Effects of Bacteria on Receiving Waters
Resource
Affected
Streams
Reservoirs
Beaches
Estuaries
Impacts of Bacteria
Human health issues
Contamination of water supply
Human health issues
Closing of shellfish beds
Beach closings
Citations
More than 80,000 miles of streams and rivers
in non-attainment because of high fecal
conform levels (USEP A, 1998a)
Increased treatment cost of drinking water due
to bacteria contamination (USEP A, 1996)
More than 4,000 beach closings or advisories
(USEP A, 1998b)
Nearly 4% of all shellfish beds restricted or
conditional harvest due to high bacteria levels
(NOAA 1992);
More than 4,000 beach closings or advisories
(USEP A, 1998b)
2.3 Physical Impacts of Construction and Land Development Activities
This subsection describes the physical impacts of construction activities and development
conditions, which include hydrologic, geomorphic, habitat structure, thermal, and direct channel
impacts. These impacts are most visible on the urban stream. Construction and land
development impacts on stream systems are described for each of these impact categories (Table
2-11). Site differences of these impacts are also noted. Because it is very difficult to
differentiate between physical impacts that occur during construction and impacts that result
from post-development conditions, the discussion addresses physical impacts from a broader
perspective. It does not differentiate between short-term effects arising and site construction
activities from long-term impacts of post-development conditions.
Physical changes are often precipitated by changes in hydrology that result when permeable rural
and forest land is converted to impervious surfaces like pavement and rooftops and relatively
impermeable urban soils. The conversion causes a fundamental change in the hydrologic cycle
because a greater fraction of rainfall is converted to surface runoff. This change in the basic
hydrologic cycle causes a series of other impacts (Table 2-11). The stream immediately begins
to adjust its size, through channel erosion, to accommodate larger flows. Streams normally
increase their cross-sectional area by incising, widening, or often both. This process of channel
response to increases in impervious surfaces accelerates sediment transport and destroys habitat.
In addition, urbanization frequently leads to alteration of natural stream channels, such as
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
straightening or lining with concrete or rock to transport water away from developed areas more
quickly. Finally, impervious surfaces also absorb heat, thereby increasing stream temperatures
during runoff events.
Table 2-11. Physical Impacts on Streams
Impact Class
Hydrologic
Geomorphic
Habitat
structure
Thermal
Channel
modification
Specific Impacts
Increased runoff volume
Increased peak flood flow
Increased frequency of "bankfull" event
Decreased baseflow
Sediment transport modified
Channel area increase to accommodate
larger flows
Stream embeddedness
Loss of large woody debris
Changes in pool/riffle structure
Increased summer temperatures
Channel hardening
Fish blockages
Loss of first and second order streams
through storm drain enclosure
Cause(s)
Paving over natural surfaces
Compaction of urban soils
Modified flows
Channel modification
Construction
Modified flows
Stream channel erosion
Loss of riparian area
Heated pavement
Storm water ponds
Loss of riparian area
Direct modifications to the stream
system.
Figure 2-1 depicts the impacts of land development on the stream channel. At low levels of
imperviousness, the stream has a stable channel, contains large woody debris, and has a complex
habitat structure. As urbanization increases, the stream becomes increasingly unstable, increases
its cross-sectional area to accommodate increased flows, and loses habitat structure. In highly
urbanized areas, stream channels are often modified through channelization or channel
hardening. These physical changes are often accompanied by decreased water quality.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
14.00 -I
12.00
10.00
o
Enlargement Rati
*. O> CO
888
2.00-
0.00
0
*Azr-S-A'
A
S3T& A
1
A
A
Aj
^f^^
AA
A
A A
i^x^**^
i
>A
j
A
k
A
V
A x^
X
A
A
AA>X
A
A
/
0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0
Imperviousness (%)
Figure 2-1. Ultimate Channel Enlargement
(Claytor and Brown, 2000; MacRae and DeAndrea, 1999)
2.3.1 Hydrologic Impacts
The increased runoff volume that results from land development alters the hydrograph, from its
predeveloped condition (Figure 2-2). The resulting hydrograph accommodates larger flows with
higher peak-flow rates. Because storm drain conveyance systems (e.g., curbs, gutters) improve
the efficiency with which water is delivered to the stream, the hydrograph is also characterized
by a more rapid time of concentration and peak discharge. Finally, the flow in the stream
between events can actually decrease because less rainfall percolates into the soil surface to feed
the stream as baseflow. The resulting hydrologic impacts include increased runoff volume,
increased flood peaks, increased frequency and magnitude of bankfull storms, and decreased
baseflow volumes.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
I
Storm I
Higher and More
Rapid Peak Discharge
I
I
t
Pie-development
Post -development
Small
Storm
\ More Runoff Volume
Jf
^ Lower and Less
\
I \
Higher Boscflow
Figure 2-2. Altered Hydrograph in Response to Urbanization
(Schueler, 1987)
2.3.1.1 Increased Runoff Volume
Impervious surfaces and urban land use changes alter infiltration rates and increase runoff
volumes. Table 2-12 shows the difference in runoff volume between a meadow and a parking
lot. The parking lot produces approximately 15 times more runoff than a meadow for the same
storm event. Schueler (1987) demonstrated that runoff values increase significantly with the
impervious surfaces in a watershed (Figure 2-3). The increased volume of water from urban
areas is the greatest single cause of the negative impacts of urban storm water on receiving
waters. The volume causes channel erosion and loss of habitat stability, as well as an increase in
the total load of many pollutants such as sediment and nutrients.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 2-12. Hydrologic Differences Between a
Parking Lot and a Meadow
Hydrologic or Water Quality
Parameter
Runoff coefficient
Time of concentration (minutes)
Peak discharge, 2-yr, 24-h storm (ftVs)
Peak discharge rate, 100-yr storm (ftVs)
Runoff volume from 1-in. storm (ft3)
Runoff velocity @ 2-yr storm (ft/sec)
Parking Lot
0.95
4.8
4.3
12.6
3,450
8
Meadow
0.06
14.4
0.4
3.1
218
1.8
Key Assumptions: 2-yr, 24-hr storm = 3.1 in.; 100-yr storm = 8.9 in.
Parking Lot: 100% imperviousness; 3% slope; 200-ftflow length;
hydraulic radius = 0.03; concrete channel; suburban Washington 'C'
values
Meadow: 1% impervious; 3% slope; 200-ft flow length; good vegetative
condition; B soils; earthen channel
Source: Schueler, 1987.
Figure 2-3. Runoff Coefficient Versus Impervious Cover
(Schueler, 1987).
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Construction activities also cause fundamental modifications in native soils. The compaction of
urban soils and the removal of topsoil during construction decreases the infiltration capacity of
the soil, resulting in a corresponding increase in runoff (Schueler, 2000). The bulk density is a
measure of soil compaction, and Table 2-13 shows the values for different aspects of
urbanization.
Table 2-13. Comparison of Bulk
Density for Undisturbed Soils and
Common Urban Conditions
Undisturbed Soil Type
or Urban Condition
Peat
Compost
Sandy Soils
Silty Sands
Silt
Silt Loams
Organic Silts/Clays
Glacial Till
Urban Lawns
Crushed Rock Parking
Lot
Urban Fill Soils
Athletic Fields
Rights of Way and
Building Pads (85%)
Rights of Way and
Building Pads (95%)
Concrete Pavement
Surface Bulk Density
(grams/cubic
centimeter)
0.2 to 0.3
1.0
1.1 to 1.3
1.4
1.3 to 1.4
1.2 to 1.5
1.0 to 1.2
1.6 to 2.0
1.5 to 1.9
1.5 to 1.9
1.8 to 2.0
1.8 to 2.0
1.5 to 1.8
1.6 to 2.1
2.2
Note: Shading indicates "urban" conditions.
Source: Schueler, 2000.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
2.3.1.2 Increased Flood Peaks
Increased flow volume increases peak flows. Data from Sauer et al. (1983) suggest that peak
flow from large flood events (10-year to 100-year storm events) increases substantially with
urbanization. The paper presents results of a survey of urban watersheds throughout the United
States and predicts flood peaks based on watershed impervious cover and a "basin development
factor" that reflects watershed characteristics such as the amount of curb and gutter, and channel
modification. These data suggest that at 50 percent impervious cover, the peak flow for the 100-
year event can be as much as twice that in an equivalent rural watershed. Data from Seneca
Creek in Montgomery County, Maryland, suggest a similar trend. The watershed experienced
significant growth during the 1950s and 1960s. Comparison of gauge records from 1961 to 1990
to those from 1931 to 1960 suggests that the peak 10-year flow event increased from 7,300 to
16,000 cfs, an increase of more than 100 percent (Leopold, 1994).
2.3.1.3 Increased Frequency and Volume of Bankfull Flows
Stream channel morphology is more influenced by frequent (1- to 2-year) storm events, or
"bankfull" flows, than by large flood events. Hollis (1975) demonstrated that urbanization
increased the frequency and magnitude of these smaller-sized runoff events much more than the
larger events. Data from this study suggest that streams increase their 2-year bankfull discharge
by two to five times after development takes place. Many other studies have documented the
increase in flow associated with impervious cover. A study by Guay (1995) compared the 2-year
flows events before and after development in an urban watershed in Parris Valley, California, in
the 1970s and in the 1990s. The impervious level of 9 percent in the 1970s increased to 22.5
percent by the 1990s. The 2-year discharge more than doubled from 646 cfs to 1,348 cfs. A 13
percent change in impervious cover resulted in a doubling of the 2-year peak flow.
A significant impact of land development is the frequency with which the bankfull event occurs.
Leopold (1994) observed a dramatic increase in the frequency of the bankfull event in Watts
Branch, an urban subwatershed in Rockville, Maryland. This watershed also experienced
significant development between the 1950s and 1960s. A comparison of gauge records indicated
that the bankfull storm event frequency increased from two to seven times per year from 1958 to
1987.
2.3.1.4 Changes in Baseflow
Land development results in a smaller recharge to groundwater and a corresponding decrease in
stream flow during dry periods (baseflow). Only a small amount of evidence, however,
documents this decrease in baseflow. Spinello and Simmons (1992) demonstrated that baseflow
in two urban Long Island streams went dry seasonally as a result of urbanization (Figure 2-4).
Another study in North Carolina could not conclusively determine that urbanization reduced
baseflow in some streams in that area (Evett et al., 1994). It is important to note, however, that
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
groundwater flow paths are often complex. Water supplying baseflow feeding the stream can be
from deeper aquifers or can originate in areas outside the surface watershed boundary. In arid
and semiarid areas, watershed managers have reported that baseflow actually increases in urban
areas. Increased infiltration from people watering their lawns and return flow from sewage
treatment plants are two possible sources (Caraco, 2000). Recharge of clean groundwater is
important in these communities, and managers would rather see clean water infiltrated than
transported as surface water during storm events.
f 195? I 1961 I 1965 i
1959
|S3 Caimans
U MassapiKjya
j Pines Brook
Connetquot
|_3 EMImore
tJ Valley Stream
Figure 2-4. Baseflow in Response to Urbanization:
Nassau County, NY
(Spinello and Simmons, 1992)
2.3.2 Impacts on Geomorphology/Sediment Transport
Changes in hydrology, combined with additional sediment sources from construction and
modifications to the stream channel, result in changes to the geomorphology of stream systems.
These impacts include increased, and sometimes decreased, sediment transport and channel
enlargement to accommodate larger flows.
2.3.2.1 Increased Transport of Sediment
The increased frequency of bankfull (1- to 2-year) storms causes more "effective work" (as
defined by Leopold), causing greater sediment transport and bank erosion to take place within
the channel. For the same storm event, the increased volume results in a greater amount of total
stress above the critical shear stress required to move bank sediment (Figure 2-5). This effect is
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
compounded by the fact that smaller, more frequent storm events also cause flows in excess of
the stress required to move sediment.
WE-OEVELOPM6NT
LEGEND
(Q)
PLOW AT WHICH SEDIMENT
TRANSPORT IS WITIATSD
2 V6AB ngCUHRENCE INTERVAL
PEAK FLOW RATE
PRE
POST
PRE-DEVELOPMENT
POST-DC V6LOPME NT
Figure 2-5. Increased Shear Stress from an Urban Hydrograph
(Schueler, 1987)
The result of this change in effective work on stream banks is increased channel erosion. Studies
in California (Trimble, 1997) and Austin, Texas (Dartinguenave et al., 1997) suggest that 60 to
75 percent of the sediment transport in urban watersheds is from channel erosion as compared to
estimates of between 5 percent and 20 percent for rural streams (Collins et al., 1997; Walling and
Woodward, 1995). If the sediment is not deposited in the channel at obstructions, it is
transported downstream to receiving waters such as lakes, estuaries, or rivers. The result can be
reduced storage and habitat due to the filling of these water bodies.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
The clearing and grading of land for new construction at the outset of urbanization is another
source of sediment in urban streams. Figure 2-6 (from Leopold, 1968) illustrates the difference
in sediment from uncontrolled and controlled construction sites.
100,000
180.000
S 10.800
= 1000
50
Annual sediment production per square mik for urbamwd and nstunl areas. Zonei;
tural; C, «nd« construction; CO. under «>n-.iruct!«i and undiluted.
tgrirol-
Figure 2-6. Sediment Production from Construction Sites
(Leopold, 1968)
2.3.2.2 Decreased Sediment Transport
Decreased sediment transport off the land surface itself can result after urbanization as natural
drainage and first-order channels are replaced by storm drains and pipes (Figure 2-7). Channel
erosion downstream might result when any export of sediment is not replaced by diminished
upstream sediment supply. Ultimately, after significant erosion has taken place, the downstream
channel will have adjusted to its post-development flow regime and sediment transport will be
reduced. Hence, the stability of the land surface and the piping of drainage channels limit storm
water's exposure to sediment and reduce the sediment supply.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
i mi
Figure 2-7. Drainage Network of Rock Creek, Maryland
Before and After Urbanization
(Dunne and Leopold, 1978)
2.3.2.3 Increase in Size of Channel
Channels increase their cross-sectional area to respond to higher and more frequent urban flows.
In post-development urban watersheds, the increase in frequency of this channel-forming event
normally causes sediment transport to be greater than sediment supply. The channel widens
(and/or downcuts) in response to this change in sediment equilibrium (Allen and Narramore,
1985; Booth, 1990 Hammer, 1977; Morisawa and LaFlure, 1979;). Some research suggests that
over time channels will reach an "ultimate enlargement," relative to a predeveloped condition,
and that impervious cover can predict this enlargement ratio (MacRae and DeAndrea, 1999).
This was shown in Figure 2-3, which depicted the relationship between ultimate stream channel
enlargement and impervious cover for alluvial streams, based on data from Texas, Vermont, and
Maryland. Figure 2-8 shows the channel expansion that has taken place and is projected to occur
in Watts Branch near Rockville, Maryland, in response to urbanization.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Historic cross section
Current cross section
Ultimate cross section ?
UJ
Cross Section Stations (ft) Looking Downstream
Figure 2-8. Channel Enlargement in Watts Branch, Maryland (Schueler, 1987)
Note: Cross sections have been overlaid for illustration purposes only. Actual sections do not share the same datum.
Stream channels expand by incision, widening, or both. Incision occurs when the stream down-
cuts and the channel expands in the vertical direction. Widening occurs when the sides of the
channel erode and the channel expands horizontally. Either method results in increased transport
of sediment downstream and degradation of habitat. Channel incision is often limited by grade
control from bedrock, large substrate, bridges, or culverts. These structures impede the
downward erosion of the stream channel and limit incision. In substrates such as sand, gravel,
and clay, however, stream incision can be of greater concern (Booth, 1990).
Channel widening more frequently occurs when streams have grade control and the stream cuts
into its banks to expand its cross-sectional area. Urban channels frequently have artificial grade
control due to the frequent culverts and road crossings. These are often areas where sediment
can accumulate as a result of undersized culverts and bridge crossings.
2.3.3 Changes in Habitat Structure
Land development results in many changes in habitat structure, including embeddedness,
decreased riffle/pool quality, and loss of large woody debris (LWD). Increased sedimentation
due to clearing and grading during construction resulting from bank erosion can significantly
reduce the amount of habitat for substrate-oriented species.
2.3.3.1 Embeddedness
Increased sediment transport from construction and land development can fill the interstitial
spaces between rocks and riffles, which are important habitat for macroinvertebrates and fish
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
species, such as darters and sculpins. The stream bottom substratum is a critical habitat for trout
and salmon egg incubation and embryo development (May et al., 1997).
2.3.3.2 Large Woody Debris (LWD)
The presence and stability of LWD is a fundamental habitat parameter. LWD can form dams and
pools, trap sediment and detritus, provide stabilization to stream channels, dissipate flow energy,
and promote habitat complexity (Booth et al., 1996). For example, depending on the size of the
woody debris and the stream, the debris can create plunge, lateral, scour, and backwater pools,
short riffles, undercut banks, side channels, and backwaters, and create different water depths
(Spence et al., 1996). The runoff generated in urban watersheds from small storms can be
enough to transport LWD. Maxted et al. (1994) found that woody debris were typically buried
under sand and silt in urban streams. In addition, the clearing of riparian vegetation limits an
important source of large woody debris. Horner et al. (1996) present evidence from the Pacific
Northwest (Figure 2-9) that LWD in urban streams decreases with increased imperviousness.
600
a SOD i-
* 400 i -
' '
''
g 200 4-»-i-*-
§, i *
100
*
»
*« * 4
10
20
30 40
Tola! Impervious Area (%J
80
SO
70
Figure 2-9. Large Woody Debris as a Function of Watershed Imperviousness
(Horner et al., 1996)
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
2.3.3.3 Changes in Stream Features
Habitat diversity is a key factor in maintaining a diverse and well-functioning aquatic
community. The complexity of the habitat results in increased niches for aquatic species.
Sediment and increases in flow can reduce the residual depths in pools and decrease the diversity
of habitat features such as pools, riffles, and runs. Richey (1982) and Scott et al. (1986) reported
an increase in the prevalence of glides and a corresponding altered pool/riffle sequence due to
urbanization.
2.3.4 Thermal Impacts
Summer in-stream temperatures have been shown to increase significantly (5 to 12 degrees) in
urban streams because of direct solar radiation, runoff from heat-absorbing pavement, and
discharges from storm water ponds (Galli, 1991). Increased water temperatures can prevent
temperature-sensitive species from surviving in urban streams. Figure 2-10 shows the increase in
water temperature resulting from urbanization.
U-,
£
3
fj
m
CL
I
e
rt
^
«#«#
CO
Delta-T
Mean
« Maximum
10 20 30 40 50 60 70 80 90 100
Cover
Figure 2-10. Stream Temperature Increase in Response to Urbanization
(Galli, 1991)
Water temperature in headwater streams is strongly influenced by local air temperatures. Galli
(1991) reported that stream temperatures throughout the summer are higher in urban watersheds,
and the degree of warming appears to be directly related to the imperviousness of the
contributing watershed. Over a 6-month period, five headwater streams in the Maryland
Piedmont that have different levels of impervious cover were monitored. Each urban stream had
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
mean temperatures that were consistently warmer than that of a forested reference stream, and
the size of the increase appeared to be a direct function of watershed imperviousness. Other
factors, such as a lack of riparian cover and ponds, were also shown to amplify stream warming,
but the primary contributing factor appeared to be watershed impervious cover.
2.3.5 Direct Channel Impacts
2.3.5.1 Channel Straightening and Hardening/Reduction in First-Order Streams
Channel straightening and hardening includes the addition of riprap or concrete to the channel,
the straightening of natural channels, and the piping of first-order and ephemeral streams.
Although this conversion process often becomes necessary to control runoff from urbanized
areas, adverse impacts often occur downstream. In a national study of urban watersheds in 269
gauged basins, Sauer et al. (1983) determined that channel straightening and channel lining
(hardening)along with the percentage of curbs and gutters, streets, and storm sewerswere the
dominant land use variables affecting storm flow. These variables all affect the efficiency with
which water is transported to the stream channel. Maintaining this efficiency increases the
velocities needed for storm water to exceed critical shear stress velocities, eroding the channel.
These factors also considerably degrade any natural habitat for stream biota.
2.3.5.2 Fish Blockages
Infrastructure associated with urbanizationsuch as bridges, dams, and culvertscan have a
considerable effect on the ability offish to move freely upstream and downstream in the
watershed. This in turn can have localized effects on small streams, where nonmigratory fish
species can be inhibited by the blockage from recolonizing areas after acutely toxic events.
Anadromous fish species such as shad, herring, salmon, and steel head also can be blocked from
making the upstream passage that is critical for their reproduction.
2.3.6 Site Differences in Physical Impacts
Site differences that can affect physical impacts include location of the impervious surfaces,
presence of vegetation, and soil type within the watershed. Location of the impervious
development can be instrumental in the timing of runoff in a watershed. If the development is at
the bottom of the watershed, peak flow from the urbanized area will likely have passed
downstream before the flow peaks from the upper watersheds reach the urbanized area (Sauer et
al., 1983). Vegetation can reduce channel erosion from storm flows. A study in British
Columbia showed that meander bends with vegetation were five times less likely to experience
significant erosion from a major flood than similar non-vegetated meander bends (Beeson and
Doyle, 1995). The types and porosity of soils are also important in determining runoff
characteristics from the land surface and erosion potential of the channels. Allen and Narramore
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
(1985) showed that channel enlargement in chalk channels was from 12 to 67 percent greater
than in shale channels near Dallas, Texas. They attributed the differences to greater velocities
and shear stress in the chalk channels.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Section 3 Description of Assessment Methodology
3.1 Introduction
This section describes EPA's methodology to assess the environmental impacts of the
construction and development category. The methodology was used by EPA to quantify the
potential environmental and economic benefits that would result from implementation of the
proposed regulatory options. These quantified benefits are enumerated in Section 4 of this
document.
The methodology described in this section focuses on impacts related to pollutant loadings
discharged from construction sites. EPA used total suspended solids (TSS) to indicate pollutant-
related benefits for proposed options.
3.2 Methodology to Estimate Pollutant Loadings from Construction Runoff Water
Discharges
EPA's methodology for estimating construction site pollutant loadings builds upon the
methodology used in the Economic Analysis of the Final Phase II Storm Water Rule (USEPA,
1999). This report (referred to herein as the Phase n EA):
Estimated the annual number of construction sites or starts covered under Phase I and
Phase n programs
Developed detailed "model construction sites" to represent a range of construction site
types, sizes and locations to estimate national construction site TSS loadings (3 site sizes, 5
slopes, and 15 climatic regions)
Estimated suspended solids loadings with and without a suite of BMPs.
The Phase II EA estimated that in the absence of any controls, construction sites on average
generate approximately 40 tons of TSS per acre per year. In addition, the Phase n EA estimated
that properly designed, installed and maintained erosion and sediment (E&S) control BMPs, in
combination, can potentially achieve a 90 to 95 percent reduction in sediment runoff. The suite
of E&S BMPs evaluated in EPA's Phase II EA is shown in Table 3-1.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-1. Common Construction Erosion and
Sediment Control BMPs
BMP Description
Silt Fence
Runoff Diversion
Mulch
Seed and Mulch
Construction Entrance
Stone Check Dam
Sediment Trap
Sediment Pond
Erosion Control3
Yes
Yes
Yes
Yes
Sediment Control"
Yes
Yes
Yes
Yes
a. Erosion controls are those distributed throughout the site to help
retain soil in place.
b. Sediment controls are intended to intercept eroded soils preventing
runoff from the construction site.
The analysis conducted by EPA indicates that environmental benefits would be achieved by
implementing procedures that ensure good E&S practices and that establish design criteria and
installation for construction site BMPs. The suite of BMPs considered by EPA in its effluent
guidelines development is presented in Table 3-2.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-2. Site BMPs Evaluated by EPA For Effluent Guidelines
Development
BMP Description
Application Rationale
Design/Installation Criteria
Sediment Basins
Sediment Traps
Mulch
PAMa
Standardization to 3,600 cubic feet of storage per watershed acre for
sites > 10 acres.
Applicable to sites > 10 acres.
Mulching of any denuded surface would be required within 2 weeks of
final grade.
PAM would be used as a temporary stabilization method until final
cover can be installed. EPA assumed that PAM is appropriate for 20
percent of construction sites.
Site Administration BMPs
E&S Site Inspections
and Certification
(a) Certify completion of SWPPP,
(b) Certify installation of BMPs,
(c) Conduct inspections every 14 days,
(d) Remove sediment from basins and traps periodically, and
(e) Certify that the site has been stabilized prior to filing NOT.
a PAM: Polyacrylamide
Implementing these BMPs as part of the proposed Option 1 is expected to achieve benefits due
to:
Higher installation rates because certification would be required;
Certification of BMP implementation that creates a verifiable record of site E&S controls;
Higher BMP maintenance frequency due to proposed inspection requirements.
In addition, Option 2 is expected to achieve additional benefits due to:
Shorter no-control periods due to more timely application of erosion BMPs;
Standardization of design/sizing criteria (Codification of BMP designs under Option 2
would result in higher removal efficiencies).
Under the proposed options EPA estimates increased efficiency, as measured by the pounds of
eroded material retained on construction sites, to range from 5 to 15 percent for Option 1 and 20
percent for Option 2. The lower and upper percentages of net performance for Option 1 yield
upper and lower bounds of reductions in construction site loadings discharged to the
environment, respectively. These ranges indicate potential additional reductions in suspended
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
solid discharges as a result of regulatory implementation, and do not account for states with
equivalent construction programs and for acres not covered by the proposed guidelines. To
account for these two factors, EPA developed additional steps to lower its estimates of TSS
loadings reductions.
For Option 2, EPA also reduced the estimated loadings to discount sites between 1 and 5 acres in
size. These sites would not be regulated under proposed Option 2 effluent guidelines, and
constitute approximately 15 percent of annually developed acreage. EPA discounted TSS
loadings reductions estimates by 15 percent to account for the fact that these sites would not be
affected by Option 2.
As detailed in Appendix A, EPA performed an evaluation of state construction general permits
and regulations to estimate the percentage of national acreage developed annually that is
currently covered under regulation that is equivalent to or exceeds the proposed option levels.
EPA evaluated states, focusing on those with annual developed acreage greater than 50,000
acres. Overall, EPA estimated that approximately 41 percent of developing acreage is currently
subject to regulatory requirements equivalent to or exceeding those under Options 1 and 2. EPA
surveyed the following four proposed requirements:
1. 3,600 cubic feet per acre storage requirement for sediment basins on sites > 10 acres
2. Certification of BMPs at installation
3. 14-day or more frequent inspection
4. 14-day cover for erosion and dust control.
To account for states currently performing at or above the levels designated under Option land 2,
EPA reduced estimated TSS loading estimates by 41 percent to remove states with equivalent
programs. The results of EPA's loadings assessment are provided in Section 4.
3.3 Characterizing the Nation's Stream Network
To evaluate environmental impacts related to stream size and length, EPA characterized stream
densities in 19 "ecoregions" for the contiguous United States (Figure 3-1). Detailed
methodologies are explained in Appendix B. The 19 ecoregions were developed based on the
stream density of large river systems, a relatively coarse assessment. Next, EPA performed a
characterization or inventory to estimate a typical stream density within each region, and to
define a statistically "standard" watershed for each ecoregion. EPA first determined the stream
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
network based on stream orders1, assessing approximately 100,000 acres in each ecoregion. The
analysis estimated the average number, acreage, slope, and length of streams, as well as the ratio
of stream orders and their drainage area. EPA used those data to estimate the total stream miles
in each ecoregion's standard watershed. Because EPA focused on land development, regional
stream densities were established through spatial and statistical averaging of actual stream
networks at the developing fringe of existing metropolitan areas.
Figure 3-1. Ecoregions for Stream Inventorying
Only one metropolitan area was analyzed for each ecoregion because of the extensive amount of
data processed to define stream networks based on 30 meter digital elevation data for 100,000
acres.
1 Stream Order is a hierarchal ordering of streams based on the degree of branching. A first order stream
is an unbranched or unforked stream. Two first-order streams flow together to make a second-order
stream; two second- order streams combine to make a third-order stream. First-order watersheds in
EPA's ecoregion-specific standard watersheds occupy between 20 and 50 acres.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
EPA's stream inventory focused on relatively small watersheds that terminate in a small
perennial stream (e.g., a fourth-order stream in the mid-Atlantic area). Intermittent and small
perennial streams are expected to be the water bodies most adversely affected by the activities of
the construction and land development industry. Less emphasis was placed on the inventory and
evaluation of larger perennial rivers (i.e., greater than fifth-order in the mid-Atlantic area)
because they potentially have more pollutant sources and isolating the benefits of the proposed
effluent guidelines in these water bodies could potentially be difficult.
The results of EPA's assessment of stream information in each of the 19 ecoregion standard
watersheds are presented in Table 3-3. In general, whenever EPA determined it should to
estimate impacts related to the total mileage of streams located within a defined acreage, EPA
used these values to convert the acreage to stream miles on the basis of stream order.
Information in the table (i.e., number and stream length) was also used to scale-up the impacts on
a stream order basis.
Table 3-3. Results of the National Stream Survey
Eco-
Region
1
2
3
Reach
Order
1
2
3
4
1
2
3
4
1
2
3
4
Number
of
Segments
Analyzed
608
104
22
7
742
166
34
9
829
179
35
9
General
Ratio of
Stream
Orders*
87
15
3
1
82
18
4
1
92
20
4
1
Average
Segment
Length, ft
428
1,078
o o T3
J,JZJ
6,914
499
1,185
2,801
4,297
423
1,017
2,307
9,367
Average
Slope of
River, ft/ft
3.06%
1.75%
1.07%
0.81%
11.25%
7.37%
5.25%
4.51%
3.11%
2.00%
1.29%
0.62%
Average
Watershed
Acreage per
Segment
53.07
273.35
1,597.67
6,425.88
45.78
228.24
1,194.55
4,434.78
53.08
266.69
1,316.02
8,283.03
Drainage Area
Ratio of Upstream
Channels to the
Downstream
Channel**
0
5.15
5.84
4.02
0
4.99
5.23
3.71
0
5.02
4.93
6.29
June 2002
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-3. Results of the National Stream Survey
Eco-
Region
4
5
6
7
8
9
Reach
Order
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Number
of
Segments
Analyzed
961
209
45
8
862
201
47
10
961
209
45
8
862
201
47
10
638
141
35
8
645
123
28
8
General
Ratio of
Stream
Orders*
120
26
6
1
86
20
5
1
120
26
6
1
86
20
5
1
80
18
4
1
81
15
4
1
Average
Segment
Length, ft
309
591
1,259
6,411
434
825
1,751
3,835
371
779
1,372
4,724
351
954
2,028
5,850
302
612
1,340
3,058
356
631
2,170
7,322
Average
Slope of
River, ft/ft
2.81%
1.62%
1.03%
0.50%
0.52%
0.40%
0.28%
0.17%
4.37%
3.20%
2.45%
1.13%
6.22%
3.21%
1.81%
0.84%
1.08%
0.72%
0.52%
0.31%
0.43%
0.50%
0.34%
0.14%
Average
Watershed
Acreage per
Segment
29.55
129.62
556.92
4,417.34
57.35
398.05
2,119.32
6,114.79
29.55
138.31
554.87
3,369.25
42.56
229.2
1,096.47
5,447.43
27.43
123.19
580.24
2,112.57
27.31
127.26
845.78
5,134.48
Drainage Area
Ratio of Upstream
Channels to the
Downstream
Channel**
0
4.39
4.3
7.93
0
6.94
5.32
2.89
0
4.68
4.01
6.07
0
5.39
4.78
4.97
0
4.49
4.71
3.64
0
4.66
6.65
6.07
June 2002
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-3. Results of the National Stream Survey
Eco-
Region
10
11
12
13
14
15
Reach
Order
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Number
of
Segments
Analyzed
1,238
275
59
14
1,050
198
41
10
960
215
50
12
753
161
43
12
933
194
44
13
1,424
290
58
11
General
Ratio of
Stream
Orders*
88
20
4
1
105
20
4
1
80
18
4
1
63
13
4
1
72
15
3
1
129
26
5
1
Average
Segment
Length, ft
306
742
1,421
4,392
353
859
1,595
3,241
376
801
2,162
3,054
272
587
1,311
6,152
427
865
1,635
2,073
381
697
1,469
3,315
Average
Slope of
River, ft/ft
3.35%
2.05%
1.27%
0.70%
3.71%
2.04%
1.29%
0.81%
14.71%
9.29%
5.95%
4.15%
22.47%
14.88%
9.97%
3.77%
5.78%
3.50%
2.38%
1.35%
3.86%
2.29%
2.05%
1.07%
Average
Watershed
Acreage per
Segment
30.89
158.44
691.2
4,339.58
30.89
158.44
691.2
4,339.58
34.1
155.93
867.6
3,082.49
21.96
107.42
497.52
3,738.79
37.21
171.65
720.88
2,563.73
31.84
143.06
545.11
2,680.10
Drainage Area
Ratio of Upstream
Channels to the
Downstream
Channel**
0
5.13
4.36
6.28
0
5.13
4.36
6.28
0
4.57
5.56
3.55
0
4.89
4.63
7.51
0
4.61
4.2
3.56
0
4.49
3.81
4.92
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-3. Results of the National Stream Survey
Eco-
Region
16
17
18
19
Reach
Order
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Number
of
Segments
Analyzed
1,009
224
53
14
464
79
21
6
251
50
13
3
457
102
27
7
General
Ratio of
Stream
Orders*
72
16
4
1
77
13
4
1
84
17
4
1
65
15
4
1
Average
Segment
Length, ft
463
1,064
2,170
4,309
464
1,605
3,018
5,392
381
697
1,469
3,315
463
1,064
2,170
4,309
Average
Slope of
River, ft/ft
8.12%
5.09%
3.92%
2.56%
20.60%
14.51%
9.47%
4.27%
3.86%
2.29%
2.05%
1.07%
8.12%
5.09%
3.92%
2.56%
Average
Watershed
Acreage per
Segment
39.77
191.81
888.83
4,293.71
57.02
395.06
1,823.06
6,881.95
31.84
143.06
545.11
2,680.10
39.77
191.81
888.83
4,293.71
Drainage Area
Ratio of Upstream
Channels to the
Downstream
Channel**
0
4.82
4.63
4.83
0
6.93
4.61
3.77
0
4.49
3.81
4.92
0
4.82
4.63
4.83
Notes:
A stream "segment" is a single stream reach between upstream and downstream confluence points.
* The "General Ratio of Stream Orders" value indicates the number of streams of "X" order found in a single
fourth order watershed.
** The "Drainage Area Ratio of Upstream Channels to the Downstream Channel" indicates the ratio of
drainage areas based on full watershed area of each stream order.
3.3.1 Characterizing the Stream Network within Developing Acreage
Although the information contained in the table can be used to convert acreage into estimated
stream miles for the 19 ecoregions it is not sufficient to estimate the number of stream miles
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
contained within the land area developed each year. To calculate that estimate, EPA first
estimates the number of acres developed and the geographic region in which the developing acres
are located. EPA used geographically linked annual development rates in the U.S. from the
National Resources Inventory (NRI) (USDA, 2000). The NRI captures data on land cover and
use, soil erosion, prime farmland soils, wetlands, habitat diversity, selected conservation
practices, and related resource attributes at more than 800,000 scientifically selected sample sites.
NRI estimated the development rate for hundreds of individual watersheds that cover the
contiguous states. To estimate the annual development rate for each of the 19 ecoregions, EPA
summed the development rates of all watersheds within the boundary of each ecoregion.
The NRI was used for assessing the impacts of the construction and land development industry
because it provides a consistent and periodic national assessment of land development trends and
employs a standard methodology for the entire nation. In addition, the NRI also provides
information on land use prior to development (e.g., the acres of farm land converted into
residential use). EPA's analysis of the most current NRI information available (rates of land
development from 1992 to 1997) is shown in Table 3-4, which shows that the current rate of land
development is approximately 2 million acres per year.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-4. Land Development Annually in Ecoregions
(Adapted from USD A, 2000)
Eco region
1
2
o
6
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Totals
Acres
Developed
Annually
64,236
91,015
34,424
338,378
67,107
127,511
42,321
252,790
330,635
326,850
97,386
249,748
35,090
38,822
11,093
57,947
28,799
12,592
12,607
2,219,352
Percent of
National Total
2.9%
4.1%
1.6%
15.2%
3.0%
5.7%
1.9%
11.4%
14.9%
14.7%
4.4%
11.3%
1.6%
1.7%
0.5%
2.6%
1.3%
0.6%
0.6%
Miles of Streams
Within Developed
Acres
134
303
61
957
137
387
82
1,075
805
686
181
757
113
152
42
149
58
47
32
6,160
Values provided indicate total acres developed. Approximately, sites < 1
acres constitute 2 percent of acres developed, and sites between 1 and 5 acres
constitute 15% of the acres developed.
Table 3-4 also provides EPA's estimate of the miles of stream contained within the acres
developed annually. When estimating the total miles of stream per ecoregion by stream order,
EPA first estimated the number of fourth-order watersheds developed. For example, in
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
ecoregion 19, the number of acres developed annually (12,607) was divided by the number of
acres in a fourth-order watershed (4,293) to yield the number of developed watersheds (2.9).
This number was then multiplied by the average number of feet per fourth-order stream (4,309)
and by the stream order ratio (1) to yield the number of feet of fourth-order streams in developed
areas (12,496). In order to find the total number of stream feet for the ecoregion, these steps are
repeated for third, second and first order streams and the sum taken of each order of stream feet.
3.3.2 Characterizing the Flow Conditions in Stream Network
Table 3-5 shows the estimated division of perennial and intermittent streams by stream order for
each ecoregion. The designations provided in Table 3-5 are based on best professional judgment.
EPA notes that third- and fourth-order streams in relatively arid areas of the nation could be
perennial due to small dams and lakes; however, the analysis assumes they are intermittent in
nature.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-5. Characterization of Stream Orders for Ecoregions
Eco region
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1st Order
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
2nd Order
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
3rd Order
I
I
I
P
P
P
P
P
P
P
P
P
I
I
P
P
P
I
P
P
4th Order
I
I
P
P
P
P
P
P
P
P
P
P
I
I
P
P
P
I
P
P
P = Perennial; I = Intermittent
EPA estimated the total miles of intermittent and perennial streams based on a cross-product of
information on Tables 3-3, 3-4 and 3-5 (total stream lengths by order, ecoregion development
rates, and perennial/intermittent assumptions, respectively). The results of this calculation are
shown in Table 3-6.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-6. Characterization of Stream Length by Flow Type
for Ecoregions
Eco region
1
2
o
J
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Geographic Name
Midwest
Southwest Arid
Southwest
Coastal Atlantic
Atlantic Shoreline
North Florida
South Florida
New England
Appalachia
Great Lakes Region
Mississippi Outlet
Mississippi West
Upper Midwest & Dakotas
Midwest Central
Pacific Coastal Region
Southern California
Willamette Valley
Eastern Washington
Sierras
Total
Baseline Conditions
Perennial
Stream Miles
0
0
7
196
25
77
19
197
198
147
38
159
0
0
8
32
13
0
7
1,123
Intermittent
Stream Miles
134
303
54
762
112
310
63
878
608
539
143
598
113
152
34
117
45
47
25
5,036
3.3.3 Converting Stream Miles into Impact Estimates
Inventorying stream information for each of the ecoregions and estimating the miles of stream
contained within urbanizing acreage provides a basis for estimating impacts that are proportional
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
to stream length. EPA developed data sets which indicate stream type (perennial or intermittent),
stream order, and location (ecoregion). The data, however, are not sufficiently customized at the
local/regional level to permit detailed environmental modeling of stream impacts on an ecoregion
basis. Hence, EPA estimated environmental changes at the national level.
Table 3-6 shows national and ecoregion-specific estimates of the river miles contained within the
acres developed annually, if all acres developed were within a single watershed. Additional
adjustment is necessary to account for the fact that development is not consolidated in a single
land mass but rather is dispersed among areas not currently under construction. See Figure 3-2.
To estimate the miles of streams potentially impacted under baseline conditions, EPA considered
a range of assumptions about the ratio of construction to non-construction area within
watersheds. As shown in Figure 3-2, EPA assumed that an area of 10 times larger than the total
area under construction is also impacted from runoff from construction in addition to runoff from
urban areas, forests and agriculture.
Land Use Type Distribution Across Watershed
Existing Urban Area (25% Under Scenario 1)
Farm/Pasture Area (32.5% Under Scenario 1)
Forested Area (32.5% Under Scenario 1)
Construction This Year (10% Under Scenario 1)
Stream Channels
Figure 3-2. Land Use Distribution of a Watershed.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Given this assumption, a construction rate of 2.2 million constructed acres per year means that
streams dispersed in 22 million acres of land area are potentially impacted by construction site
runoff in combination with runoff from urban, forested and farm land. Based on EPA's
assessment of stream lengths contained in the 19 ecoregions and the rates of development in each
ecoregion, EPA estimates that roughly 10,000 perennial stream miles and 36,000 intermittent
stream miles are potentially affected by construction site runoff annually (Table 3-7).
Table 3-7. Estimated Miles of Streams Potentially Affected
by One Year's Construction
Ecoregion
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Geographic Name
Midwest
Southwest Arid
Southwest
Coastal Atlantic
Atlantic Shoreline
North Florida
South Florida
New England
Appalachia
Great Lakes Region
Mississippi Outlet
Mississippi West
Upper Midwest & Dakotas
Midwest Central
Pacific Coastal Region
Southern California
Willamette Valley
2.2 Million Acres
(Acreage Constructed
Annually )
Perennial
Stream Miles
-
-
7
196
25
197
198
147
159
-
-
8
32
13
Intermittent
Stream Miles
107
242
43
609
90
702
486
431
478
91
121
27
93
36
22 Million Acres
(Assumed Land Area
Containing Acreage
Constructed Annually )
Perennial
Stream Miles
0
0
70
1,960
250
1,970
1,980
1,470
1,590
0
0
80
320
130
Intermittent
Stream Miles
1,070
2,420
430
6,090
900
7,020
4,860
4,310
4,780
910
1,210
270
930
360
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-7. Estimated Miles of Streams Potentially Affected
by One Year's Construction
Ecoregion
18
19
Geographic Name
Eastern Washington
Sierras
Total
2.2 Million Acres
(Acreage Constructed
Annually )
Perennial
Stream Miles
-
7
989
Intermittent
Stream Miles
38
20
3,614
22 Million Acres
(Assumed Land Area
Containing Acreage
Constructed Annually )
Perennial
Stream Miles
0
70
9,890
Intermittent
Stream Miles
380
200
36,140
Notes:
EPA assumed that all streams within fourth-order watersheds are intermittent in regions 1,2, 13, 14, and 18.
Total values reflect a 20 percent reduction in intermittent stream miles to account for streams that are
expected to be converted into below grade pipe systems. Values also discount stream miles in Ecoregions 6, 7,
and 11 because these systems are greatly influenced by man-made channel networks and natural wetland
systems (i.e., are less hierarchal in nature).
EPA then developed a simple stream model to assess potential changes in TSS concentrations
during wet-weather periods for the estimated 61 thousand miles of streams receiving discharges
from construction sites annually. EPA evaluated three development scenarios to estimate the
range of potential TSS reductions in streams within watersheds experiencing construction runoff,
as shown in Table 3-8. The three development scenarios are intended to represent low,
moderate, and high levels of urbanization, over which construction activities are superimposed.
EPA used a simple mass balance approach to estimate in stream TSS concentrations, as follows:
1. Estimate the average annual runoff from each land use condition, from construction
acreage affected, and not affected by proposed guideline options.
2. Estimate the average annual TSS loading from each land use condition, based on EPA-
estimated or literature reported event mean concentration (EMC) for TSS.
3. Estimate national average change in the in-stream concentration of TSS using land use
fractions given in each of the three scenarios in Table 3-8. This assessment is performed
for all 2.2 million acres developed annually, based on the total estimated runoff volume in
a single (typical) rainfall year.
Table 3-8, also shows the allocation of regulated construction sites for Options 1 and 2. Under
Option 1, approximately 0.2 percent of the watershed is assumed to be covered by construction
sites less than 1 acres in size. The runoff from these acres is not affected by Option 1 proposed
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
requirements. Under Option 2, approximately 1.7 percent of the watershed is assumed to be
covered by construction sites less than 5 acres in size. The runoff from these acres are not
affected by Option 2 proposed requirements. Runoff coefficients (Table 3-9) indicate the portion
of rainfall that leaves the area as runoff. The remainder is assumed to infiltrate into the ground or
evaporate. Values were selected based on EPA estimates of percent imperviousness, values
reported in literature, and best professional judgement.
Table 3-8. Active Construction Site Runoff Scenarios
for Option 1 and Option 2
Land Use Conditions
Existing Urban Area
Forested
Farm
Sites Regulated Under Option 1
Sites Not Affected by Option 1
Sites Regulated Under Option 2
Sites Not Affected by Option 2
Land Use Coverage Scenarios
Low
Urbanization
25.0%
32.6%
32.6%
9.80%
0.20%
8.27%
1.73%
Moderate
Urbanization
50.0%
20.1%
20.1%
9.80%
0.20%
8.27%
1.73%
High
Urbanization
75.0%
7.6%
7.6%
9.80%
0.20%
8.27%
1.73%
Table 3-9. Runoff Coefficients for
Land Uses
Land Use Conditions
Existing Urban Area
Forested
Farm
Construction3
Runoff Coefficients
0.46
0.05
0.15
0.80
a. Includes sites regulated under Option 1, not
affected by Option 1, regulated under Option 2, and
not affected by Option 2.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
EPA's simple in-stream model estimates the potential reduction in TSS concentration during
wet-weather periods. EPA's approach does not taken into account the contributions of base flow
and base flow loads (i.e., that entering streams due to groundwater) during wet-weather periods.
Excluding this base flow results in an overestimation of actual TSS concentrations.
Because rainfall conditions affect the results of EPA's assessment, an evaluation of
approximately 30 years of rainfall records for 1,200 rainfall gauges was performed to identify a
typical rainfall year for each of the 19 ecoregions.2 Based on this evaluation, EPA estimated that
the national average rainfall depth falling on construction sites is approximately 34.8 inches per
year. This estimate is a weighted average, based on the acres developed in each ecoregion.
Table 3-10 presents the event mean concentrations (EMCs) used by EPA to estimate the range of
TSS loadings. In selecting EMC values, EPA used values from the literature that would help
create reasonable upper and lower bound estimates. High and low effectiveness estimates for
construction site effluent concentrations were matched with lower bound and upper bound
EMCs, respectively, for other land uses. For example, lower bound and upper bound EMC
values for urban runoff (141 and 224 mg/L) were assumed to bracket urban concentrations, and
to indicate TSS annual loadings. Only forested area EMCs were held constant for both lower and
upper bound estimates. In terms of annual TSS yield, EPA's assumed EMCs for urban areas
correspond to 0.26 and 0.41 tons per acre per year. Annual TSS yield for farm/pasture, equates
to 0.15 and 3.0 tons per acre per year (Corsi et al., 1997; Novotny and Chesters, 1981; Horner et
al., 1986; Horner, 1992; and Sonzogni et al., 1980).
EPA assumed that construction sites not affected by the proposed effluent guidelines would
discharge TSS in concentrations similar to those estimated under baseline conditions. This
assumption may overestimate TSS loadings estimates associated with Option 2 for sites between
1 and 5 acres. The results of EPA's simple national in stream model, based on the data and
assumptions described above, are provided in Section 4.
2 EPA defined a "typical rainfall year" as having a total rainfall depth within 10 percent of the average
for the ecoregion, and not containing a single rainfall event with greater than a 2-year storm.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table 3-10. Runoff EMCs for Acres Within a Watershed
(TSS in mg/L)
Land Use Condition
Urban Area
Forested/Pasture
Farm
Regulated Construction Sites
Construction Sites Not Affected by
Regulations
Lower Bound
Option 1
141
152
254
2,613
3,765
Option 2
141
152
254
1,843
3,765
Upper Bound
Option 1
224
152
5,071
6,529
6,914
Option 2
224
152
5,071
5,081
6,914
Notes:
Urban TSS Concentrations are from USEPA, 1993
Option 1 high and low effectiveness assumes construction BMPs are installed/operated so
resulting capture of TSS generation is 80 and 50% of TSS generation, respectively.
Option 2 high and low effectiveness assumes construction BMPs are installed/operated so
resulting capture of TSS generation is 90 and 70% of TSS generation, respectively.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Section 4 Environmental Benefits Assessment of Evaluated Regulatory
Options
This section presents the Agency's estimates of the environmental benefits that would result from
implementation of erosion and sediment controls during construction activities. EPA evaluated 3
regulatory options for controlling discharges from active construction sites. Table 4-1 describes
each of the options.
Table 4-1. Regulatory Options Evaluated for Controlling Discharges
from Construction Activities
Option
Option 1
Option 2
Option 3
Description
Applicable to construction sites with one acre or more of disturbed land
Operators required to:
- Inspect site throughout land disturbance period
- Certify that the controls meet the regulatory design criteria as applicable
Amend NPDES regulations at 40 CFR Part 122 (no new effluent guideline regulations)
Applicable to construction sites with five acres or more of disturbed land
Operators required to:
- Prepare storm water pollution prevention plan
- Design, install, and maintain erosion and sediment controls
- Inspect site throughout land disturbance period
- Certify that the controls meet the regulatory design criteria as applicable
Creates a new effluent guidelines category at 40 CFR Part 450 and amends Part 122
regulations
No new regulatory requirements
The following subsections present Agency estimates of regulatory conditions for suspended
solids loadings and resulting improvements to the environment, including stream habitat.
4.1 Total Suspended Solids Loadings
Construction projects involve a series of temporary activities (e.g., land clearing, grubbing,
building), and, with the exception of large-scale facilities, these projects generally have a
duration of less than a year. During the construction period, erosion and sediment control (ESC)
BMPs are employed to minimize pollutant discharges.
EPA used three criteria as a basis for selecting which pollutants to use as indicators of
construction site pollutant loadings: (1) pollutants that correlate strongly with the construction
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
activities, (2) toxic pollutants should be considered only if dissolved concentrations are high, and
(3) proposed effluent guidelines would significantly reduce loadings from current levels. Based
on these criteria, EPA selected eroded soils/sediment loadings (e.g., measured by TSS and!4
turbidity) as the indicator of construction site pollutant loadings. Other runoff constituents are
either present in low concentrations or account for such a small proportion of the total discharge
that conventional treatment would not prove effective in removing additional levels beyond that
attained in treating the suspended solid component.
Table 4-2 presents EPA's estimates of construction site loadings reductions under Options 1, 2
and 3 in terms of tons of TSS per year.
Table 4-2. Estimated TSS Loadings Reductions for
Proposed Regulatory Options
Lower bound
estimates
Upper bound
estimates
Incremental Percent TSS
captured by BMPs
Annual reductions (tons)
Incremental Percent TSS
captured by BMPs
Annual reductions (tons)
Option 1
5%
2,637,569
15%
7,912,707
Option 2
25%
11, 126,639 a
25%
11, 126,639 a
Option 3
0
0
0
0
a. Option 2 reductions were reduced by approximately 15 percent to account for sites between
1 and 5 acres in size not covered by this option.
As shown in the table, EPA estimates that under Option 1, construction sites would increase the
removal rate of TSS by approximately 5 to 15 percent. The projected increase in net
performance of construction site BMPs under Option 2 is about 25 percent. These estimates
were developed using the Agency's engineering judgement, but are based on the following
assumptions:
Regulatory options would require that sediment ponds are certified at the time of
installation to ensure they are built as designed
Implementation of the proposal would result in more effective selection, installation and
O&M of ESC BMPs due to inspection and certification of site activities.
Option 2 would result in shorter duration of exposure for un-managed denuded areas
The regulatory options loadings were generated using three factors: total annual number of acres
developed, tons per year of suspended solids per acre of land undergoing development, and
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
incremental improvement in BMP performance under the regulatory options. As described in
Section 3, NRI data were used to estimate that approximately 2.2 million acres are developed
annually and the estimate of 40 tons per acre generation of TSS at construction sites was based
on the Phase II Storm Water Economic Assessment (EPA, 1999).
Estimated annual sediment loadings reductions from implementation of EPA's proposed
alternatives range from 0 tons (Option 3: no new regulations) to approximately 11 million tons
per year for Option 2.
4.2 Total Suspended Solid In-Stream Concentrations
Although the Agency did not attempt to quantify aquatic losses (e.g., fish kills, habitat loss), it
did estimate how construction loadings impact in-stream concentration levels of TSS in receiving
water bodies.
Because in-stream concentrations of TSS result from mixtures of point and nonpoint sources that
cannot cannot be readily separated, EPA estimated in-stream TSS concentrations for three
different land use scenarios that assumed 10 percent of the land area was under construction and
90 percent was distributed among three types of land uses: forest, farm and urban. As shown in
Table 4-3, the land use scenarios were developed to characterize different levels of urbanization,
ranging from 25 percent urban in scenario 1 to 75 percent urban in scenario 3. EPA's analysis
does not assess in-stream settling and resuspension. In addition, there are other sources of TSS
that have not been included in the analysis, such as loads resulting from commercial point source
discharges and loads resulting from increased stream bank erosion related to higher stream flow
rates and velocities in urbanizing water bodies. TSS loadings (section 4.1) were used in
conjunction with different event mean concentration (EMC) values, runoff coefficients, and ESC
BMP efficiency rates to generate TSS in-stream concentrations, as described in section 3.3.3.
Table 4-3. Development Scenarios Used to Estimate Impacts
of Regulatory Options
Development Scenario
1 . Low Urbanization
2. Moderate Urbanization
3. High Urbanization
Land Use Proportions
25% Urban,
50% Urban,
75% Urban,
10%
10%
10%
Construction,
Construction,
Construction,
32.5% Farm,
20% Farm,
7.5% Farm,
32.5% Forest
20%
Forest
7.5% Forest
Different land use scenarios were evaluated because of the differences in TSS characteristics that
result as land becomes developed from rural to urban conditions. The high urban conditions
contribute the lowest levels of TSS while the low urbanization contribute the highest levels of
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
TSS. This can be explained by the fact that forest and farm practices generate higher levels of
sediment runoff and urbanized areas create more storm water runoff, diluting TSS
concentrations.
Table 4-4 shows the estimated concentration reductions in TSS from the regulatory options.
Reductions in TSS concentrations under Option 1 are estimated to range from 68 to 348 mg/L.
TSS concentrations under Option 2 would decrease from 276 to 489 mg/L. The larger reductions
from regulatory Option 2 reflect the more stringent proposed requirements resulting in higher
ESC BMP effectiveness. Reductions from the lower bound comparisons are higher than
reductions in the upper bound comparisons.
Table 4-4. Estimated Average In-Stream TSS Concentrations Reduction,
mg/L
Development Scenario
1. Low Urbanization
2. Moderate Urbanization
3. High Urbanization
High Effectiveness Estimates
Option 1
348
258
205
Option 2
489
363
289
Low Effectiveness Estimates
Option 1
116
86
68
Option 2
466
346
276
Note: The results provided in this table could overestimate the differences between the effects of
high and low urbanization because the study did not include discharges from commercial point
sources or from increased stream bank erosion resulting from increased stream flow rates and
velocities in urbanized areas. If these factors had been included, the concentrations under high
urbanization would likely have been significantly higher.
4.3 Miscellaneous Impacts
Sites under construction have hydrologic responses that differ from those under pre-development
conditions; both the peak discharge and duration of high discharges increase dramatically.
(Appendix C describes hydrologic changes caused by construction and the effects of commonly
employed sedimentation ponds on site discharge.) As a result, EPA believes that construction
sites increase the potential for flooding of downstream areas above the levels found in the pre-
development condition. Both Options 1 and 2 are expected to reduce flooding potential by
ensuring the installation and maintenance of sedimentation ponds (if already present) that retain
site runoff and help minimize flooding potential.
Poor ESC BMP implementation has an adverse impact on aesthetics of affected water bodies
lowering the visual quality of streams and lakes by creating high turbidity levels. Sediment
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
enriched runoff from failing construction site ESC BMPs convey sediment to adjacent land
creating a visual nuisance and sometimes requiring clean up. Although EPA did not estimate the
environmental or economic benefits associated with improvements in these conditions, EPA
believes that both Option 1 and 2 would reduce these impacts significantly by requiring closer
tracking of ESC BMP operation, problem identification, and problem resolution.
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Branch Watershed Plan. City of Rockville, MD. Center for Watershed Protection.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
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Appendix A
Evaluating Pollutant Loadings from Construction Activities
that Potentially Impact the Environment
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Appendix A Evaluating Pollutant Loadings from Construction Activities
that Potentially Impact the Environment
This appendix details aspects of the methodologies described in Section 3 to pollutant discharges
that result from construction activities under two options. Specifically, it expands on the
discussion presented in Section 3, providing additional information on the assumptions used by
EPA in its assessment.
Estimates of Affected Area
The Phase IINPDES storm water rule economic analysis (USEPA, 1999) presented information
on the size and nature of construction activities under the Phase I and n storm water programs.
In addition, the Phase II economic analysis (EA) detailed an extensive analysis of pollutant
loadings for a range of site sizes, soil types, land slopes, and locations. EPA's current evaluation
uses the results presented in the Phase II report to update its overall estimate of national
construction site loadings. EPA expects that new regulation of the construction and development
(C&D) category will augment the existing state and Phase INPDES storm water programs. In
addition, new regulations will shape future development of construction programs expected
under the Phase n NPDES storm water program.
EPA identified the array of potentially affected construction sites in the nation. EPA's assessment
of construction site loadings is based on regulation of approximately 2.17 million acres per year.
This regulated acreage estimate was calculated based on estimated national development rates
from the 1997 National Resources Inventory (USDA, 2000), less the estimated acreage either
occupied by sites less than 1 acre in size (not regulated) or sites which receive Phase II "R"
waivers. "R" waivers are those applied for and granted under the construction general permit for
sites with very low erosivity. The Phase n EA estimated the total acreage granted "R" waivers to
be approximately 33 thousand acres (approximately 1.8 percent of the total constructed acreage).
Based on its assessment of probable construction site size distribution, EPA estimates that
another 1.7 percent of the annual constructed acreage will be on sites less than 1 acre. In
addition, under Option 1, EPA is considering removing sites smaller than 5 acres. EPA estimates
that approximately 18 percent of construction occurs on sites less than 5 acres in area.
EPA's Analysis of State Programs
Table A-l presents the results of EPA's analysis of state construction programs. EPA focused on
the states with the largest annual construction footprint to estimate the level of current control
(i.e., not all state regulations were reviewed). As a result, the absence of a "Yes" value in Table
A-l may indicate that a construction program was not evaluated by EPA. Overall, the results in
Table A-l were converted into a ecoregion "score" or the percent of developed acreage that
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would gain greater management under EPA's options. Table A-2 indicates the resulting
percentage of construction acreage affected by the potential effluent guidelines in each ecoregion.
As expected, new BMPs required under the options (e.g., certification of sediment basins) were
not found in existing state regulations, and overall, existing state requirements require option-
level BMPs for approximately 30-35 percent of the acreage developed annually.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Table A-l. Assessment of State Construction Control Programs
State/Territory
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of
Columbia
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Minimum of 3600
Cubic Feet per Acre
Storage Requirement
for Larger Sites
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
14-Day or
More
Inspection
Frequency
Yes
Yes
Yes
Yes
14- Day
Cover
Required
Yes
Yes
Yes
Yes
Yes
Yes
Yes
States with Less than
20 Inches of
Precipitation Per
Year
Yes
Yes
Yes
Yes
Yes
Yes
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State/Territory
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Minimum of 3600
Cubic Feet per Acre
Storage Requirement
for Larger Sites
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
14-Day or
More
Inspection
Frequency
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
14- Day
Cover
Required
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
States with Less than
20 Inches of
Precipitation Per
Year
Yes
Yes
Yes
Yes
Yes
Yes
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State/Territory
Wyoming
Minimum of 3600
Cubic Feet per Acre
Storage Requirement
for Larger Sites
14-Day or
More
Inspection
Frequency
Yes
14- Day
Cover
Required
States with Less than
20 Inches of
Precipitation Per
Year
Yes
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Table A-2. Percentage of Acreage Developed Without Option Equivalent Requirements
Eco region
ER1
ER2
ER3
ER4
ER5
ER6
ER7
ER8
ER9
ER10
ER11
ER12
ER13
ER14
ER15
ER16
ER17
ER18
ER19
National
Average
Weighted by
Land
Developed
3600 Cubic Feet per
Acre Storage in
Sedimentation
Basins for Larger
Sites
(Criterion 1)
28.96%
39.16%
0.00%
77.06%
65.74%
100.00%
100.00%
64.45%
50.16%
74.51%
71.53%
51.80%
89.38%
67.34%
62.15%
5.65%
100.00%
100.00%
100.00%
64%
Certification of
Sediment Basins
(Criterion 2)
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0%
14-Day or more
frequent
inspection
(Criterion 3)
28.25%
57.61%
10.66%
77.06%
65.74%
100.00%
100.00%
68.16%
55.30%
81.79%
71.70%
65.17%
32.32%
53.83%
100.00%
100.00%
100.00%
100.00%
100.00%
70%
14- Day Cover For
Wet-States, or
none required for
dry states
(Criterion 4)
30.72%
57.61%
10.66%
77.06%
65.74%
100.00%
100.00%
64.45%
42.80%
81.79%
71.70%
65.17%
89.38%
71.01%
100.00%
100.00%
100.00%
100.00%
100.00%
69%
Overall
Weighted
Percentage of
Acres Without
Coverage
24.7%
47.1%
8.0%
65.5%
55.9%
85.0%
85.0%
56.6%
43.4%
68.8%
60.9%
54.1%
47.4%
51.4%
81.2%
75.6%
85.0%
85.0%
85.0%
58.9%
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Information in Table A-2 was converted into an overall national "score," to discount estimated
TSS loadings reductions by accounting for acres covered by equivalent programs. To combine
the four analyzed criteria, EPA assumed that the individual contributions to reductions were 10,
15, 50, 25 percent, respectively. For example, sedimentation basins based on 3,600 cubic feet
contribute 10 percent of the estimated reduction between baseline and option loadings. On a
national basis, EPA estimated that approximately 41 percent of land is served by equivalent
programs, and would not be affected by Option 1 or 2 requirements.
June 2002 A-7
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Appendix B
Inventorying of Streams Potentially Impacted By
Construction Activities
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Appendix B Inventorying of Streams Potentially Impacted By
Construction Activities
Overview
This appendix describes EPA's effort to inventory and assess environmental impacts of
construction activities. Specifically, the appendix describes, in detail, the analytical steps
performed to inventory the nation's stream system and provides general background information
on the rationale used to develop the inventory approach. Delineation of impacted stream
environments forms the basis for assessing the future benefits of regulatory controls on
construction and activities.
The objectives of this appendix are as follows:
To describe a method to characterize streams by their hydrologic function based on regional
differences
To establish the appropriate map scale for inventorying streams based on their size and
geometry (e.g., length, slope, dimensions).
Stream Characterization
Many of the impacts on streams are a function of drainage area and hydrologic regime.
Producing a national summary of potentially impacted stream networks is challenging because
the nature and size of streams vary significantly throughout the country. For example,
watersheds that produce a minimum base flow of 1 cubic foot per second (cfs) occupy 1 square
mile in the eastern United States but require 100 square miles in the arid southwest. To account
for this variation, EPA divided the country into 19 large hydrologic regions and then further
inventoried the streams in each region separately, based on approximate stream size categories
(i.e., stream orders). Representative watersheds in each of the 19 large ecoregions in the
contiguous U.S. (see Figure B-l) were inventoried to determine the average stream density for
the stream orders that are the most likely impacted in each ecoregion.
EPA developed the boundaries for the 19 ecoregions based on a stream density assessment that
used EPA's Reach File 1 (RF1) stream network and the 76 ecoregions developed by Omernik
(1987). Figure B-2 shows the RF1 densities in terms of acres per stream mile for each of the 76
ecoregions. Combining the 76 ecoregions into the 19 ecoregions shown in Figure B-l helps
simplify the analysis while still capturing a reasonable number of regions with similar stream
densities and accounts for gross changes in hydrology, land forms, soil types, and potential
natural vegetation.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
In general, the literature indicates that environmental sensitivity (e.g., geomorphologic changes,
pollutant toxicity) is greater on smaller stream orders, from the intermittent headwater streams to
small perennial streams. For most environmental impacts (except perhaps nutrient loadings), the
impacts of the construction and land development industry tend to decrease with increased
stream size, and the impacts tend to become confounded with other influences (e.g., other point
and nonpoint source pollutant loads). For this reason, the inventory focused on relatively small
watersheds (between 2 and 7 square miles) to better assess the impacts of hydrologic changes on
small streams.
Figure B-l. Regions for Stream Inventorying
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Figure B-2. Stream Densities for Omernik Ecoregions
(in units of acres per stream mile)
Because EPA focused on small streams, it was necessary to select a method by which to
characterize streams by size. Historically, various schemes have been created to characterize and
count streams within a drainage network, including the following:
Stream order is determined by counting stream segments starting with the smallest stream
channels found on a selected map scale.
Stream level is determined by counting stream segments starting from the most downstream
discharge point (ocean or estuary) on a selected map scale.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Streams are characterized by physical descriptions including flow frequency (perennial or
intermittent streams), size (large, medium, or small), and/or terms such as swales, creeks,
and rivers.
Watershed size is based on the scale of the map on which the watersheds are just visible.
EPA selected the first method, stream order characterization, for use in this assessment.
Map Scale Selection
Because any network of "streams" identified at the outset of a hydrologic inventory is highly
dependent on the scale of the map used, selecting the appropriate scale is a critical step. Rills
and swales that are obvious and identifiable on a l:2,400-scale map are completely absent on a
1:250,000-scale map. Figure B-3 shows the streams visible on the following three scales of maps
for a typical watershed (10 square miles) in northeastern Maryland:
U.S. Geological Survey (USGS) 1:250,000-scale map or streams found in EPA's RF1
stream network
USGS 1:100,000-scale map or streams found in EPA's Reach File V. 3 (RF3) and National
Hydrography Dataset (NHD) (USGS, 2000) stream networks
USGS l:24,000-scale map.
The three map scales, respectively, permit successively finer viewing of stream sizes: (1) large
perennial streams, (2) medium perennial to intermittent streams, and (3) larger swales and
intermittent streams. Although not shown in Figure B-3, an even finer detail stream
networkone based on 1:2,400-scale maps (a scale commonly used by local governments) that
includes the smallest swalescan be visualized by increasing the number of 1:24,000-scale
streams threefold (i.e., delineation of watersheds as small as 2 acres). Figure B-3 illustrates the
importance of map scale selection:
Inventorying stream networks based on 1:24,000-scale will include many more streams than
a l:250,000-scale inventory;
The stream order assigned to any stream will be different based on the map scale; and
Direct evaluation using only EPA's RF1 and RF3 hydrologic stream coverages would
grossly undercount the number of streams potentially impacted.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Stream Network Scale
EPARF1 = 1:250,000
EPARF3 = 1:100,000
Swale = 1:24,000
A/
Figure B-3. Stream Networks for 1:250,000-, 1:100,000-, and l:24,000-Scale Maps
Note: The 1:24,000-stream network shown contains more streams than the USGS identified on its 7.5-minute
quadrangle maps using typical blue or dashed blue lines. This figure includes all swales that can be drawn
based on contour lines given on the 1:24,000 map, resulting in an enhancement that shows two to three times
more "streams" than are shown on the original map (down to watersheds approximately 10 acres in size).
Interpretation of contour lines defines a stream network based on land forms as the contours are
present because streams/swales have created them. This contour-based enhancement defines a
"stream" based on topography, regardless of whether or not the stream is actually drawn on the
map.
Because using an increased detail of stream network (smaller map scale) requires increased effort
levels, EPA developed a method that was both practical and depicted the appropriate stream level
for this assessment. The amount of stream data available is extensive; the national coverage for
RF1 contains 100 megabytes of data, while RF3 contains 7,400 megabytes. All of RF1 (data on
just the largest rivers in the nation) can reside and be analyzed on a single microcomputer.
However, the RF3 network and the similar, newer NHD are so large they can be analyzed in a
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
microcomputer environment only when divided into 20 separate parts. Therefore, EPA assumed
that a national dataset containing all streams and swales identifiable from l:2,400-scale maps
would be unworkable within the current limits of any microcomputer.
To maintain a relatively small map scale, EPA performed an inventory of streams and swales
identifiable based on l:24,000-scale maps (where swales are added manually) by first sampling
representative watersheds or areas. (An actual inventory of individual swales and streams on a
1:24,000-scale for specific acreage developed in any given state in any given year is beyond
current computational capabilities and the limits of available data, requiring some type of
approximation or sampling technique). EPA used digital elevation maps (DEMs), which allowed
EPA to process contour data, enhancing the original stream network to provide data on the larger
intermittent streams (typically streams draining less than 30 acres). Because EPA's assessment
of the construction industry indicates that a medium-sized construction start is approximately 20
acres, this approach is refined enough to inventory the number and size of streams potentially
impacted by construction and land development activities. The number and length of streams in a
larger area were then estimated by using the stream density found in the sampled watershed/area.
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Appendix C
Impacts of Construction Activities on Hydrology
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
Appendix C Impacts of Construction Activities on Hydrology
Overview
This appendix describes hydrologic changes that result from construction and post-development
activities, and focuses primarily on changes in runoff rates and soil infiltration. The general
hydrologic changes caused by these industries have environmental and economic impacts.
The objectives of this appendix are:
To demonstrate the variation in runoff rate for a 10-acre site as it changes from a forested
condition into a construction condition.
To describe the environmental benefits of current BMPs primarily designed to limit
discharge from construction sites.
Methodology
A simple hydrologic model was developed to depict the hydrologic changes that result from
construction and land development activities on a (10-acre) site. The size of 10-acres was chosen
because it represents the typical size for a construction site. In addition, the hydrologic changes
are believed to be similar to changes that result on larger sites such as 100-acre sites and 1000-
acre sites.
Investigation of hydrologic changes was performed by using two hydrologic models: TR-55 and
TR-20. These models use data developed over many years by USD A/Natural Resources
Conservation Service (NRCS), and are among the most often employed models for the
hydrologic design of hydraulic structures, such as storm drainage systems (USDA, 2002).
The 10-acre watershed was assumed to have a 50/50 mix of soils in the type B and C hydrologic
soil classification, with an average ground slope of 7 percent. Time of concentration was derived
based on standard TR-55 worksheets that analyze sheet flow, shallow concentrated flow, and
pipe flow. For the analysis, the 2-year 24-hour SCS1 type II rainfall event, totaling 3.2 inches of
rainfall, was used to conservatively estimate the runoff hydrographs.
Multiple land use conditions (Table C-l) were evaluated to help assess the hydrologic impacts
for the small 10-acre site. EPA notes that most construction sites occupying 10 acres are
1 The Soil Conservation Service (SCS) is the former name of the Natural Resources Conservation
Service (NRCS).
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
equipped with a sedimentation pond, intended to minimize sediment discharge from the site.
Although sediment ponds are not designed specifically shave the peak runoff rate (i.e., limit the
construction site peak discharge rate to be equal to or less than the peak runoff from the forested
site), these structures inherently have some capability of peak-shaving depending on the site
conditions. In addition, sedimentation ponds can be built to increase its peak-shaving capability.
For the purposes of this assessment, EPA assumed that a sedimentation pond (Condition 3)
shaves the peak completely, as shown in Figure C-l.
Table C-l. Evaluated Hydrologic Conditions for a
Land Use
Condition
1
2
o
J
Typical 10- Acre Site
Description
Pre-development: a forested land use
Construction: cleared and grubbed soil surface with no
construction runoff BMPs (No sedimentation ponds)
Construction: cleared and grubbed soil surface with no
BMPs (a sedimentation pond that also shaves the peak
development peak flow)
vegetation and without
vegetation with storm water
runoff to match the pre-
The results of the analysis are presented below for each of these land use conditions.
Discussion of Runoff Results for Modeled Land Use Conditions
Figure C-l compares the predicted runoff hydrographs for Land Use Conditions 1 through 3.
The hydrographs in the figure show the large increase in runoff volume and peak runoff rate that
occurs for construction sites with or without storm water BMPs that limit the peak runoff rates.
This increase is caused by the removal of existing vegetation and compaction of site soils with
earth moving equipment, which greatly diminishes the site's ability to absorb rainfall and limit
discharge. In fact, NRCS data strongly suggest that a fully-constructed site (e.g., a residential
neighborhood) produces less runoff than a denuded site under construction, even though
impervious surfaces (e.g., driveways, roofs) have not yet been installed.
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
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Figure C-l. Runoff Hydrographs for a 10-Acre Construction Site
Although the implementation of peak-shaving BMPs minimizes some of the flooding
downstream of a construction site due to high peak flows, it does not eliminate the potential for
enhanced flooding that is caused by longer durations of high-flow discharges. Table C-2
indicates that the construction site produces high flows for a much greater duration than flows
originally released from the forested site. In fact, the 10-acre site that once produced a flow rate
equal to or greater than 3 cubic feet per second (cfs) for only 0.2 hours will produce more than 3
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Environmental Assessment of Construction and Development Proposed Effluent Guidelines
cfs for 3.2 hours when peak-shaving BMPs are employed during construction. Should a 2-year
storm occur during the construction period, the longer flow duration increases the chances that
the discharge will be combined with downstream peak flows from other developing/developed
locations to produce a flooding condition.
Table C-2. Comparison of Durations of High Flow Rates
for Different Land Use Conditions
Land Use Condition
Forested
Construction site without peak shaving BMPs
Construction site with peak shaving BMPs
Hours of flow equal to
or greater than:
3 cfs
0.2
0.9
3.2
2 cfs
0.3
1.4
4
Icfs
0.8
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5.7
cfs = cubic feet per second
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