Environmental
Assessment
for
Proposed
Effluent
Guidelines
and
Standards
for
the
Construction
and
Development
Category
June
2002
Environmental
Assessment
for
Proposed
Effluent
Guidelines
and
Standards
for
the
Construction
and
Development
Category
June
2002
United
States
Environmental
Protection
Agency
Office
of
Water
(4303T)
1200
Pennsylvania
Avenue,
NW
Washington,
DC
20460
www.
epa.
gov/
waterscience/
guide/

[EPA­
821­
R­
02­
009]
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
i
Contents
Section
1
Introduction
and
Background
1.1
Introduction
..........................................................
1­
1
1.2
Organization
of
Environmental
Assessment
.................................
1­
2
1.3
Review
of
Regulatory
History
Related
to
C&
D
Industries
......................
1­
3
1.3.1
Clean
Water
Act
.................................................
1­
3
1.3.1.1
NPDES
Storm
Water
Permit
Program
..........................
1­
3
1.3.2
Other
State
and
Local
Government
Storm
Water
Requirements
............
1­
4
Section
2
Categories
of
Reported
Impacts
and
Pollutants
2.1
Introduction
..........................................................
2­
1
2.2
Pollutants
Associated
with
Construction
and
Land
Development
Storm
Water
Runoff
....................................................
2­
2
2.2.1
Sediment
......................................................
2­
2
2.2.1.1
Sources
of
Sediment
.......................................
2­
2
2.2.1.2
Receiving
Waters
Impacts
...................................
2­
5
2.2.2
Metals
........................................................
2­
7
2.2.2.1
Sources
of
Metal
Runoff
....................................
2­
8
2.2.2.2
Metals
Impacts
on
Receiving
Waters
..........................
2­
10
2.2.3
PAHs,
and
Oil
and
Grease
........................................
2­
11
2.2.3.1
Sources
of
PAHs,
and
Oil
and
Grease
........................
2­
11
2.2.3.2
Receiving
Water
Impacts
...................................
2­
12
2.2.4
Pathogens
....................................................
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
and
Land
Development
Activities
.............
2­
16
2.3.1
Hydrologic
Impacts
.............................................
2­
18
2.3.1.1
Increased
Runoff
Volume
..................................
2­
19
2.3.1.2
Increased
Flood
Peaks
.....................................
2­
22
2.3.1.3
Increased
Frequency
and
Volume
of
Bankfull
Flows
.............
2­
22
2.3.1.4
Changes
in
Baseflow
......................................
2­
22
2.3.2
Impacts
on
Geomorphology/
Sediment
Transport
......................
2­
23
2.3.2.1
Increased
Transport
of
Sediment
.............................
2­
23
2.3.2.2
Decreased
Sediment
Transport
..............................
2­
25
2.3.2.3
Increase
in
Size
of
Channel
.................................
2­
26
2.3.3
Changes
in
Habitat
Structure
......................................
2­
27
2.3.3.1
Embeddedness
...........................................
2­
27
2.3.3.2
Large
Woody
Debris
(LWD)
................................
2­
28
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
ii
2.3.3.3
Changes
in
Stream
Features
.................................
2­
29
2.3.4
Thermal
Impacts
...............................................
2­
29
2.3.5
Direct
Channel
Impacts
..........................................
2­
30
2.3.5.1
Channel
Straightening
and
Hardening/
Reduction
in
First
Order
Streams
.............................................
2­
30
2.3.5.2
Fish
Blockages
...........................................
2­
30
2.3.6
Site
Differences
in
Physical
Impacts
................................
2­
30
Section
3
Description
of
Assessment
Methodology
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
Stream
Miles
into
Impact
Estimates
.......................
3­
14
Section
4
Environmental
Benefits
Assessment
of
Evaluated
Regulatory
Options
4.1
Total
Suspended
Solids
Loadings
.........................................
4­
1
4.2
Total
Suspended
Solid
In­
Stream
Concentrations
.............................
4­
3
4.3
Miscellaneous
Impacts
..................................................
4­
4
Section
5
References
.......................................................
5­
1
Appendices
A.
Evaluating
Pollutant
Loadings
from
Construction
Activities
that
Potentially
Impact
the
Environment
......................................................
A­
1
B.
Inventorying
of
Streams
Potentially
Impacted
by
Construction
Activities
..........
B­
1
C.
Impacts
of
Construction
Activity
on
Hydrology
..............................
C­
1
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
Sediment
in
Urban
Areas
.................................
2­
4
Table
2­
3.
Source
Area
Concentrations
for
TSS
in
Urban
Areas
....................
2­
4
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
iii
Table
2­
4.
Sediment
Impacts
on
Receiving
Waters
..............................
2­
6
Table
2­
5.
Metal
Sources
and
Hot
Spots
in
Urban
Areas
..........................
2­
9
Table
2­
6.
Metal
Source
Area
Concentrations
in
Urban
Areas
....................
2­
10
Table
2­
7.
Metals
Impacts
on
Receiving
Waters
................................
2­
11
Table
2­
8.
Effects
of
PAHs
and
Oil
and
Grease
on
Receiving
Waters
...............
2­
13
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
...........................
2­
15
Table
2­
10.
Effects
of
Bacteria
on
Receiving
Waters
.............................
2­
16
Table
2­
11.
Physical
Impacts
on
Streams
......................................
2­
17
Table
2­
12.
Hydrologic
Differences
Between
a
Parking
Lot
and
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.
Site
BMPs
Evaluated
by
EPA
for
Effluent
Guidelines
Development
........
3­
3
Table
3­
3.
Results
of
the
National
Stream
Survey
...............................
3­
6
Table
3­
4.
Land
Development
Annually
in
Ecoregions
.........................
3­
11
Table
3­
5.
Characterization
of
Stream
Orders
for
Ecoregions
.....................
3­
13
Table
3­
6.
Characterization
of
Stream
Length
by
Flow
Type
for
Ecoregions
.........
3­
14
Table
3­
7.
Estimated
Miles
of
Streams
Potentially
Affected
by
One
Year's
Construction
...................................................
3­
16
Table
3­
8.
Active
Construction
Site
Runoff
Scenarios
for
Option
1
and
Option
2
.....
3­
18
Table
3­
9.
Runoff
Coefficients
for
Land
Uses
.................................
3­
18
Table
3­
10.
Runoff
EMCs
for
Acres
Within
a
Watershed
.........................
3­
20
Table
4­
1.
Regulatory
Options
Evaluated
for
Controlling
Discharges
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
Impacts
of
Regulatory
Options
....
4­
3
Table
4­
4.
Estimated
Average
In­
Stream
TSS
Concentrations
Reduction
.............
4­
4
Figures
Figure
2­
1.
Ultimate
Channel
Enlargement
....................................
2­
18
Figure
2­
2.
Altered
Hydrograph
in
Response
to
Urbanization
.....................
2­
19
Figure
2­
3.
Runoff
Coefficient
Versus
Impervious
Cover
........................
2­
20
Figure
2­
4.
Baseflow
in
Response
to
Urbanization:
Nassau
County,
NY
.............
2­
23
Figure
2­
5.
Increased
Shear
Stress
from
an
Urban
Hydrograph
....................
2­
24
Figure
2­
6.
Sediment
Production
from
Construction
Sites
........................
2­
25
Figure
2­
7.
Drainage
Network
of
Rock
Creek,
Maryland,
Before
and
After
Urbanization.
.............................................
2­
26
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
iv
Figure
2­
8.
Channel
Enlargement
in
Watts
Branch,
Maryland
.....................
2­
27
Figure
2­
9.
Large
Woody
Debris
as
a
Function
of
Watershed
Imperviousness
........
2­
28
Figure
2­
10.
Stream
Temperature
Increase
in
Response
to
Urbanization
..............
2­
29
Figure
3­
1.
Ecoregions
for
Stream
Inventorying
.................................
3­
5
Figure
3­
2.
Land
Use
Distribution
of
a
Watershed
...............................
3­
15
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
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
of
fish
spawning
access
due
to
new
road
crossings
June
2002
1­
1
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
1­
2
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
Description
Option
1
°
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)

Option
2
°
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
Option
3
°
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
1­
3
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
NPDES
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
Environmental
Assessment
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June
2002
1­
4
°
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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2002
2­
1
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.
Environmental
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2­
2
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
of
fish
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).
Environmental
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2002
2­
3
Table
2­
1.
Studies
of
Soil
Erosion
as
TSS
From
Construction
Sites
Site
Mean
Inflow
TSS
Concentration
(mg/
L)
Source
Seattle,
Washington
17,500
Horner,
Guerdy,
and
Kortenhoff,
1990
SR
204
3,502
Horner,
Guerdy,
and
Kortenhoff,
1990
Mercer
Island
1,087
Horner,
Guerdy,
and
Kortenhoff,
1990
RT1
359
Schueler
and
Lugbill,
1990
RT2
4,623
Schueler
and
Lugbill,
1990
SB1
625
Schueler
and
Lugbill,
1990
SB2
415
Schueler
and
Lugbill,
1990
SB4
2,670
Schueler
and
Lugbill,
1990
Pennsylvania
Test
Basin
9,700
Jarrett,
1996
Georgia
Model
1,500
–
4,500
Sturm
and
Kirby,
1991
Maryland
Model
1,000
–
5,000
Barfield
and
Clar,
1985
Uncontrolled
Construction
Site
Runoff
(MD)
4,200
York
and
Herb,
1978
Austin,
Texas
600
Dartiguenave,
EC
Lille,
and
Maidment,
1997
Hamilton
County,
Ohio
2,950
Islam,
Taphorn,
and
Utrata­
Halcomb,
1998
Mean
TSS
(mg/
L)
3,681
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.
Environmental
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2002
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4
Table
2­
2.
Sources
of
Sediment
in
Urban
Areas
Source
Area
Loading
Bank
erosion
°
Up
to
75
percent
in
California
and
Texas
studies
Overland
flow
°
Lawns
­
average
value
of
geometric
means
from
4
studies:
201
mg/
L
Runoff
from
areas
with
exposed
soils
°
Average
value:
3,640
mg/
L
Blown­
on
material
and
organic
matter
°
May
account
for
as
much
as
35
to
50
percent
in
urban
areas
Bannerman
et
al.,
1993;
Dartinguenave
et
al.,
1997;
Schueler,
1987;
Steuer
et
al.,
1997;
Trimble,
1997;
Waschbusch
et
al.,
2000;

Table
2­
3.
Source
Area
Concentrations
for
TSS
in
Urban
Areas
Source
Area
TSS
(mg/
L)
a
TSS
(mg/
L)
b
TSS
(mg/
L)
c
Monroe
Basin
Harper
Basin
Commercial
parking
lot
110
58
51
High­
traffic
street
226
232
65
Medium­
traffic
street
305
326
51
Low­
traffic
street
175
662
68
69
Commercial
rooftop
24
15
18
Residential
rooftop
36
27
15
17
Residential
driveway
157
173
34
Residential
lawn
262
397
59
122
a
Steuer
et
al.,
1997.
b
Bannerman
et
al.,
1993.
c
Waschbusch
et
al.,
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
to15
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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2002
2­
5
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
Impacts
of
Sediment
Indicator
Source
Streams
Loss
of
sensitive
species
and
a
decrease
in
fish
and
macroinvertebrate
diversity
communities
GA
loss
of
sensitive
species
at
25
NTU
Kundell
and
Rasmussen,
1995
Clogging
of
gills
and
loss
of
habitat
Leopold,
1973
Decreased
flow
capacity
in
streams
Maryland
decreased
flow
capacity.
Increased
overbank
flows
Barrett
and
Molina,
1998
Interference
with
water
quality
processes.
Affects
transport
of
contaminants
MacRae
and
Marsalek,
1992
Wetlands
Deposition
of
sediment
High
accretion
rates
in
a
tidal
wetland
as
a
result
of
sediment
transport
in
an
urbanized
watershed
Pasternack,
1998
Loss
of
sensitive
species:
amphibians,
plants
Loss
of
amphibian
species
Horner,
1996
Loss
of
seven
wetland/
SAV
plant
species
since
European
development
Hilgartner,
1986
Reservoirs
Turbidity
results
in
increased
costs
of
treatment
for
drinking
water
more
abatement
costs
at
>5
NTU
McCutcheon
et
al.,
1993
Sedimentation
results
in
decreased
storage
Beaches
Turbidity
reduces
aesthetic
value
Kundell
and
Rasmussen,
1995
Sedimentation
can
result
in
increased
accretion
rates
in
wetlands
and
change
plant
community
structure
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
Table
2­
4.
Sediment
Impacts
on
Receiving
Waters
Resource
Affected
Impacts
of
Sediment
Indicator
Source
June
2002
2­
7
Estuaries
Sedimentation
Pasternack,
1998
Turbidity
Livingston,
1996
Reduced
light
attenuation
can
lead
to
a
loss
of
submerged
aquatic
vegetation
(SAV)
Schiff,
1996
Mackiernan
et
al.,
1996
SAV
losses
due
to
sediments
and
eutrophication
Short
and
WyllieEcheverria
1996
SAV
losses
in
NE
Orth
and
Moore,
1983
Essential
habitat
requirements
for
SAV
include
light
attenuation,
dissolved
inorganic
nitrogen,
phosphorus
and
chlorophyl­
a
Stevenson
et
al.,
1993
Loss
of
seven
wetland/
SAV
plant
species
since
European
settlement
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
8
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
highconcentration
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).
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
9
Table
2­
5.
Metal
Sources
and
Hot
Spots
in
Urban
Areas
Metal
Sources
Hot
Spots
Zinc
Tires,
fuel
combustion,
galvanized
pipes
and
gutters,
road
salts
Estimate
of
60%
from
tires
a
Parking
lots,
rooftops,
and
streets
Copper
Auto
brake
linings,
pipes
and
fittings,
algacides,
and
electroplating
Estimate
of
50%
from
brake
pads
a
Parking
lots,
commercial
roofs,
and
streets
Lead
Diesel
fuel,
paints,
and
stains
Parking
lots,
rooftops,
and
streets
Cadmium
Component
of
motor
oil;
corrodes
from
alloys
and
plated
surfaces
Parking
lots,
rooftops,
and
streets
Chromium
Found
in
exterior
paints;
corrodes
from
alloys
and
plated
surfaces
More
frequently
found
in
industrial
and
commercial
runoff
a
Woodward­
Clyde,
1992
(Santa
Clara,
CA,
study)
Sources:
Barr,
1997;
Bannerman
et
al.,
1993;
Steuer,
1997
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
10
Table
2­
6.
Metal
Source
Area
Concentrations
in
Urban
Areas
(in
ug/
L)

Source
Area
Diss.
Zinc
Total
Zinc
Diss.
Copper
Diss.
Copper
Total
Copper
Diss.
Lead
Diss.
Lead
Total
Lead
Total
Lead
Total
Lead
Citation
(a)
(b)
(a)
(b)
(b)
(a)
(c)
(a)
(c)
(b)

Commercial
parking
lot
64
178
10.7
9
15
40
22
High­
traffic
street
73
508
11.2
18
46
2.1
1.7
37
25
50
Mediumtraffic
street
44
339
7.3
24
56
1.5
1.9
29
46
55
Low­
traffic
street
24
220
7.5
9
24
1.5
0.5
21
10
33
Commercial
rooftop
263
330
17.8
6
9
20
48
9
Residential
rooftop
188
149
6.6
10
15
4.4
25
21
Residential
driveway
27
107
11.8
9
17
2.3
52
17
Residential
lawn
na
59
na
13
13
na
na
na
Basin
outlet
23
203
7.0
5
16
2.4
49
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
11
Table
2­
7.
Metals
Impacts
on
Receiving
Waters
Resource
Affected
Impacts
of
Metals
Evidence
Streams
°
Chronic
toxicity
due
to
in­
stream
concentrations
and
accumulation
in
sediment
°
Bioaccumulation
in
aquatic
species
°
Acute
toxicity
at
certain
concentrations
Chronic
toxicity
increased
during
longerduration
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
toxicological
effects
(Heaney
and
Huber,
1978);
Bioaccumulation
in
crayfish
(Masterson
&
Bannerman,
1994)

Reservoirs/
Lakes
°
Accumulation
of
metals
in
sediment
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).

Estuaries
°
Accumulation
of
metals
in
sediment
°
Loss
of
SAV
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
offsite
contamination
could
occur.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
12
Post­
Development
Conditions
as
a
Source
of
PAHs,
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
kilogram—
much
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
13
Table
2­
8.
Effects
of
PAHs
and
Oil
and
Grease
on
Receiving
Waters
Resource
Affected
Impacts
of
PAHs
and
Oil
and
Grease
Citations
Streams
°
Possible
chronic
toxicity
due
to
in­
stream
concentrations
and
accumulation
in
sediment
°
Bioaccumulation
in
aquatic
species
°
Acute
toxicity
at
certain
concentrations
Bioaccumulation
in
crayfish
tissue
studies
(Masterson
and
Bannerman,
1994);
Potential
metabolic
costs
to
organisms
(Crunkilton
et
al.,
1996);
delayed
toxicity
(Ellis,
1986/
1987);
Baseflow
toxicity
(Mederios,
1983)

Reservoirs
°
Accumulation
of
PAHs
in
sediment
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)

Estuaries
°
Accumulation
of
PAHs
in
sediment
°
Potential
loss
of
SAV
°
Accumulation
of
PAHs
in
fish
and
shellfish
tissue
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
selfcontained
and
are
not
connected
to
the
land
surface.
Any
leaks
from
them
would
likely
be
identified
and
addressed
quickly.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
2­
14
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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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)
Percent
Detection
Total
Giardia
Confirmed
Giardia
Total
Cryptosporidium
Confirmed
Cryptosporidium
Wastewater
effluent
(8/
147)
41.5
12.9
15.7
5.4
Urban
subwatershed
(5/
78)
41.0
6.4
37.2
3.9
Agricultural
subwatershed
(5/
56)
30.4
3.6
32.1
3.6
Undisturbed
subwatershed
(5/
73)
26.0
0.0
9.6
1.4
Source:
Stern
et
al.,
1996.

2.2.4.2
Receiving
Water
Impacts
Fecal
coliform
bacteria,
fecal
streptococci,
and
E.
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/
100mL)
(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/
100mL
(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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Table
2­
10.
Effects
of
Bacteria
on
Receiving
Waters
Resource
Affected
Impacts
of
Bacteria
Citations
Streams
°
Human
health
issues
More
than
80,000
miles
of
streams
and
rivers
in
non­
attainment
because
of
high
fecal
coliform
levels
(USEPA,
1998a)

Reservoirs
°
Contamination
of
water
supply
Increased
treatment
cost
of
drinking
water
due
to
bacteria
contamination
(USEPA,
1996)

Beaches
°
Human
health
issues
More
than
4,000
beach
closings
or
advisories
(USEPA,
1998b)

Estuaries
°
Closing
of
shellfish
beds
°
Beach
closings
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
(USEPA,
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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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
Specific
Impacts
Cause(
s)

Hydrologic
°
Increased
runoff
volume
°
Increased
peak
flood
flow
°
Increased
frequency
of
"bankfull"
event
°
Decreased
baseflow
°
Paving
over
natural
surfaces
°
Compaction
of
urban
soils
Geomorphic
°
Sediment
transport
modified
°
Channel
area
increase
to
accommodate
larger
flows
°
Modified
flows
°
Channel
modification
°
Construction
Habitat
structure
°
Stream
embeddedness
°
Loss
of
large
woody
debris
°
Changes
in
pool/
riffle
structure
°
Modified
flows
°
Stream
channel
erosion
°
Loss
of
riparian
area
Thermal
°
Increased
summer
temperatures
°
Heated
pavement
°
Storm
water
ponds
°
Loss
of
riparian
area
Channel
modification
°
Channel
hardening
°
Fish
blockages
°
Loss
of
first
and
second
order
streams
through
storm
drain
enclosure
°
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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18
0.00
2.00
4.00
6.00
8.00
10.
00
12.
00
14.
00
0.0
10.
0
20.
0
30.
0
40.
0
50.
0
60.
0
70.
0
80.
0
Impervi
ousness
(%)
Enlargement
Ratio
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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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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Table
2­
12.
Hydrologic
Differences
Between
a
Parking
Lot
and
a
Meadow
Hydrologic
or
Water
Quality
Parameter
Parking
Lot
Meadow
Runoff
coefficient
0.95
0.06
Time
of
concentration
(minutes)
4.8
14.4
Peak
discharge,
2­
yr,
24­
h
storm
(ft
3
/s)
4.3
0.4
Peak
discharge
rate,
100­
yr
storm
(ft
3
/s)
12.6
3.1
Runoff
volume
from
1­
in.
storm
(ft
3
)
3,450
218
Runoff
velocity
@
2­
yr
storm
(ft/
sec)
8
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
ft
flow
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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21
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
Surface
Bulk
Density
(grams/
cubic
centimeter)

Peat
0.2
to
0.3
Compost
1.0
Sandy
Soils
1.1
to
1.3
Silty
Sands
1.4
Silt
1.3
to
1.4
Silt
Loams
1.2
to
1.5
Organic
Silts/
Clays
1.0
to
1.2
Glacial
Till
1.6
to
2.0
Urban
Lawns
1.5
to
1.9
Crushed
Rock
Parking
Lot
1.5
to
1.9
Urban
Fill
Soils
1.8
to
2.0
Athletic
Fields
1.8
to
2.0
Rights
of
Way
and
Building
Pads
(85%)
1.5
to
1.8
Rights
of
Way
and
Building
Pads
(95%)
1.6
to
2.1
Concrete
Pavement
2.2
Note:
Shading
indicates
"urban"
conditions.
Source:
Schueler,
2000.
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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
Environmental
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2002
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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.

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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24
compounded
by
the
fact
that
smaller,
more
frequent
storm
events
also
cause
flows
in
excess
of
the
stress
required
to
move
sediment.

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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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.

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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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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0
1
2
3
4
5
6
7
8
9
10
0
5
10
15
20
25
30
35
40
45
Cross
Section
Stations
(ft)
­
Looking
Downstream
Elevation
(ft­
msl)
Historic
Section
Curr
ent
Section
Bankfull
Depth
Ultimate
Section
?
Historic
c
ross­
section
Current
cross­
section
Ultimate
c
ross­
section
?

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
downcuts
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
Environmental
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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.

Figure
2­
9.
Large
Woody
Debris
as
a
Function
of
Watershed
Imperviousness
(Horner
et
al.,
1996)
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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.

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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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
sewers—
were
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
urbanization—
such
as
bridges,
dams,
and
culverts—
can
have
a
considerable
effect
on
the
ability
of
fish
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
Environmental
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2­
31
(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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3­
1
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
pollutantrelated
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
II
EA):

°
Estimated
the
annual
number
of
construction
sites
or
starts
covered
under
Phase
I
and
Phase
II
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
II
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
2
Table
3­
1.
Common
Construction
Erosion
and
Sediment
Control
BMPs
BMP
Description
Erosion
Control
a
Sediment
Control
b
Silt
Fence
Yes
Runoff
Diversion
Yes
Mulch
Yes
Seed
and
Mulch
Yes
Construction
Entrance
Yes
Stone
Check
Dam
Yes
Sediment
Trap
Yes
Sediment
Pond
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
3
Table
3­
2.
Site
BMPs
Evaluated
by
EPA
For
Effluent
Guidelines
Development
BMP
Description
Application
Rationale
Design/
Installation
Criteria
Sediment
Basins
Standardization
to
3,600
cubic
feet
of
storage
per
watershed
acre
for
sites

10
acres.

Sediment
Traps
Applicable
to
sites

10
acres.

Mulch
Mulching
of
any
denuded
surface
would
be
required
within
2
weeks
of
final
grade.

PAM
a
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
4
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
1and
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
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.

June
2002
3­
5
network
based
on
stream
orders
1
,
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
6
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
EcoRegion
Reach
Order
Number
of
Segments
Analyzed
General
Ratio
of
Stream
Orders*
Average
Segment
Length,
ft
Average
Slope
of
River,
ft/
ft
Average
Watershed
Acreage
per
Segment
Drainage
Area
Ratio
of
Upstream
Channels
to
the
Downstream
Channel**

1
1
608
87
428
3.06%
53.07
0
2
104
15
1,078
1.75%
273.35
5.15
3
22
3
3,323
1.07%
1,597.67
5.84
4
7
1
6,914
0.81%
6,425.88
4.02
2
1
742
82
499
11.25%
45.78
0
2
166
18
1,185
7.37%
228.24
4.99
3
34
4
2,801
5.25%
1,194.55
5.23
4
9
1
4,297
4.51%
4,434.78
3.71
3
1
829
92
423
3.11%
53.08
0
2
179
20
1,017
2.00%
266.69
5.02
3
35
4
2,307
1.29%
1,316.02
4.93
4
9
1
9,367
0.62%
8,283.03
6.29
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
Table
3­
3.
Results
of
the
National
Stream
Survey
EcoRegion
Reach
Order
Number
of
Segments
Analyzed
General
Ratio
of
Stream
Orders*
Average
Segment
Length,
ft
Average
Slope
of
River,
ft/
ft
Average
Watershed
Acreage
per
Segment
Drainage
Area
Ratio
of
Upstream
Channels
to
the
Downstream
Channel**

June
2002
3­
7
4
1
961
120
309
2.81%
29.55
0
2
209
26
591
1.62%
129.62
4.39
3
45
6
1,259
1.03%
556.92
4.3
4
8
1
6,411
0.50%
4,417.34
7.93
5
1
862
86
434
0.52%
57.35
0
2
201
20
825
0.40%
398.05
6.94
3
47
5
1,751
0.28%
2,119.32
5.32
4
10
1
3,835
0.17%
6,114.79
2.89
6
1
961
120
371
4.37%
29.55
0
2
209
26
779
3.20%
138.31
4.68
3
45
6
1,372
2.45%
554.87
4.01
4
8
1
4,724
1.13%
3,369.25
6.07
7
1
862
86
351
6.22%
42.56
0
2
201
20
954
3.21%
229.2
5.39
3
47
5
2,028
1.81%
1,096.47
4.78
4
10
1
5,850
0.84%
5,447.43
4.97
8
1
638
80
302
1.08%
27.43
0
2
141
18
612
0.72%
123.19
4.49
3
35
4
1,340
0.52%
580.24
4.71
4
8
1
3,058
0.31%
2,112.57
3.64
9
1
645
81
356
0.43%
27.31
0
2
123
15
631
0.50%
127.26
4.66
3
28
4
2,170
0.34%
845.78
6.65
4
8
1
7,322
0.14%
5,134.48
6.07
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
Table
3­
3.
Results
of
the
National
Stream
Survey
EcoRegion
Reach
Order
Number
of
Segments
Analyzed
General
Ratio
of
Stream
Orders*
Average
Segment
Length,
ft
Average
Slope
of
River,
ft/
ft
Average
Watershed
Acreage
per
Segment
Drainage
Area
Ratio
of
Upstream
Channels
to
the
Downstream
Channel**

June
2002
3­
8
10
1
1,238
88
306
3.35%
30.89
0
2
275
20
742
2.05%
158.44
5.13
3
59
4
1,421
1.27%
691.2
4.36
4
14
1
4,392
0.70%
4,339.58
6.28
11
1
1,050
105
353
3.71%
30.89
0
2
198
20
859
2.04%
158.44
5.13
3
41
4
1,595
1.29%
691.2
4.36
4
10
1
3,241
0.81%
4,339.58
6.28
12
1
960
80
376
14.71%
34.1
0
2
215
18
801
9.29%
155.93
4.57
3
50
4
2,162
5.95%
867.6
5.56
4
12
1
3,054
4.15%
3,082.49
3.55
13
1
753
63
272
22.47%
21.96
0
2
161
13
587
14.88%
107.42
4.89
3
43
4
1,311
9.97%
497.52
4.63
4
12
1
6,152
3.77%
3,738.79
7.51
14
1
933
72
427
5.78%
37.21
0
2
194
15
865
3.50%
171.65
4.61
3
44
3
1,635
2.38%
720.88
4.2
4
13
1
2,073
1.35%
2,563.73
3.56
15
1
1,424
129
381
3.86%
31.84
0
2
290
26
697
2.29%
143.06
4.49
3
58
5
1,469
2.05%
545.11
3.81
4
11
1
3,315
1.07%
2,680.10
4.92
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
Table
3­
3.
Results
of
the
National
Stream
Survey
EcoRegion
Reach
Order
Number
of
Segments
Analyzed
General
Ratio
of
Stream
Orders*
Average
Segment
Length,
ft
Average
Slope
of
River,
ft/
ft
Average
Watershed
Acreage
per
Segment
Drainage
Area
Ratio
of
Upstream
Channels
to
the
Downstream
Channel**

June
2002
3­
9
16
1
1,009
72
463
8.12%
39.77
0
2
224
16
1,064
5.09%
191.81
4.82
3
53
4
2,170
3.92%
888.83
4.63
4
14
1
4,309
2.56%
4,293.71
4.83
17
1
464
77
464
20.60%
57.02
0
2
79
13
1,605
14.51%
395.06
6.93
3
21
4
3,018
9.47%
1,823.06
4.61
4
6
1
5,392
4.27%
6,881.95
3.77
18
1
251
84
381
3.86%
31.84
0
2
50
17
697
2.29%
143.06
4.49
3
13
4
1,469
2.05%
545.11
3.81
4
3
1
3,315
1.07%
2,680.10
4.92
19
1
457
65
463
8.12%
39.77
0
2
102
15
1,064
5.09%
191.81
4.82
3
27
4
2,170
3.92%
888.83
4.63
4
7
1
4,309
2.56%
4,293.71
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
10
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
11
Table
3­
4.
Land
Development
Annually
in
Ecoregions
(Adapted
from
USDA,
2000)

Ecoregion
Acres
Developed
Annually
Percent
of
National
Total
Miles
of
Streams
Within
Developed
Acres
1
64,236
2.9%
134
2
91,015
4.1%
303
3
34,424
1.6%
61
4
338,378
15.2%
957
5
67,107
3.0%
137
6
127,511
5.7%
387
7
42,321
1.9%
82
8
252,790
11.4%
1,075
9
330,635
14.9%
805
10
326,850
14.7%
686
11
97,386
4.4%
181
12
249,748
11.3%
757
13
35,090
1.6%
113
14
38,822
1.7%
152
15
11,093
0.5%
42
16
57,947
2.6%
149
17
28,799
1.3%
58
18
12,592
0.6%
47
19
12,607
0.6%
32
Totals
2,219,352
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
12
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
13
Table
3­
5.
Characterization
of
Stream
Orders
for
Ecoregions
Ecoregion
1st
Order
2nd
Order
3rd
Order
4th
Order
1
I
I
I
I
2
I
I
I
I
3
I
I
I
P
4
I
I
P
P
5
I
I
P
P
6
I
I
P
P
7
I
I
P
P
8
I
I
P
P
9
I
I
P
P
10
I
I
P
P
11
I
I
P
P
12
I
I
P
P
13
I
I
I
I
14
I
I
I
I
15
I
I
P
P
16
I
I
P
P
17
I
I
P
P
18
I
I
I
I
19
I
I
P
P
20
I
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
14
Table
3­
6.
Characterization
of
Stream
Length
by
Flow
Type
for
Ecoregions
Ecoregion
Geographic
Name
Baseline
Conditions
Perennial
Stream
Miles
Intermittent
Stream
Miles
1
Midwest
0
134
2
Southwest
Arid
0
303
3
Southwest
7
54
4
Coastal
Atlantic
196
762
5
Atlantic
Shoreline
25
112
6
North
Florida
77
310
7
South
Florida
19
63
8
New
England
197
878
9
Appalachia
198
608
10
Great
Lakes
Region
147
539
11
Mississippi
Outlet
38
143
12
Mississippi
West
159
598
13
Upper
Midwest
&
Dakotas
0
113
14
Midwest
Central
0
152
15
Pacific
Coastal
Region
8
34
16
Southern
California
32
117
17
Willamette
Valley
13
45
18
Eastern
Washington
0
47
19
Sierras
7
25
Total
1,123
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
15
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
16
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
Geographic
Name
2.
2
Million
Acres
(Acreage
Constructed
Annually
)
22
Million
Acres
(Assumed
Land
Area
Containing
Acreage
Constructed
Annually
)

Perennial
Stream
Miles
Intermittent
Stream
Miles
Perennial
Stream
Miles
Intermittent
Stream
Miles
1
Midwest
­
107
0
1,070
2
Southwest
Arid
­
242
0
2,420
3
Southwest
7
43
70
430
4
Coastal
Atlantic
196
609
1,960
6,090
5
Atlantic
Shoreline
25
90
250
900
6
North
Florida
7
South
Florida
8
New
England
197
702
1,970
7,020
9
Appalachia
198
486
1,980
4,860
10
Great
Lakes
Region
147
431
1,470
4,310
11
Mississippi
Outlet
12
Mississippi
West
159
478
1,590
4,780
13
Upper
Midwest
&
Dakotas
­
91
0
910
14
Midwest
Central
­
121
0
1,210
15
Pacific
Coastal
Region
8
27
80
270
16
Southern
California
32
93
320
930
17
Willamette
Valley
13
36
130
360
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
Table
3­
7.
Estimated
Miles
of
Streams
Potentially
Affected
by
One
Year's
Construction
Ecoregion
Geographic
Name
2.
2
Million
Acres
(Acreage
Constructed
Annually
)
22
Million
Acres
(Assumed
Land
Area
Containing
Acreage
Constructed
Annually
)

Perennial
Stream
Miles
Intermittent
Stream
Miles
Perennial
Stream
Miles
Intermittent
Stream
Miles
June
2002
3­
17
18
Eastern
Washington
­
38
0
380
19
Sierras
7
20
70
200
Total
989
3,614
9,890
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
18
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
Land
Use
Coverage
Scenarios
Low
Urbanization
Moderate
Urbanization
High
Urbanization
Existing
Urban
Area
25.0%
50.0%
75.0%

Forested
32.6%
20.1%
7.6%

Farm
32.6%
20.1%
7.6%

Sites
Regulated
Under
Option
1
9.80%
9.80%
9.80%

Sites
Not
Affected
by
Option
1
0.20%
0.20%
0.20%

Sites
Regulated
Under
Option
2
8.27%
8.27%
8.27%

Sites
Not
Affected
by
Option
2
1.73%
1.73%
1.73%

Table
3­
9.
Runoff
Coefficients
for
Land
Uses
Land
Use
Conditions
Runoff
Coefficients
Existing
Urban
Area
0.46
Forested
0.05
Farm
0.15
Construction
a
0.80
a.
Includes
sites
regulated
under
Option
1,
not
affected
by
Option
1,
regulated
under
Option
2,
and
not
affected
by
Option
2.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
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.

June
2002
3­
19
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
3­
20
Table
3­
10.
Runoff
EMCs
for
Acres
Within
a
Watershed
(TSS
in
mg/
L)

Land
Use
Condition
Lower
Bound
Upper
Bound
Option
1
Option
2
Option
1
Option
2
Urban
Area
141
141
224
224
Forested/
Pasture
152
152
152
152
Farm
254
254
5,071
5,071
Regulated
Construction
Sites
2,613
1,843
6,529
5,081
Construction
Sites
Not
Affected
by
Regulations
3,765
3,765
6,914
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
4­
1
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
Description
Option
1
°
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)

Option
2
°
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
Option
3
°
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
4­
2
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
and14
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
Option
1
Option
2
Option
3
Lower
bound
estimates
Incremental
Percent
TSS
captured
by
BMPs
5%
25%
0
Annual
reductions
(tons)
2,637,569
11,126,639
a
0
Upper
bound
estimates
Incremental
Percent
TSS
captured
by
BMPs
15%
25%
0
Annual
reductions
(tons)
7,912,707
11,126,639
a
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
4­
3
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
Land
Use
Proportions
1.
Low
Urbanization
25%
Urban,
10%
Construction,
32.5%
Farm,
32.5%
Forest
2.
Moderate
Urbanization
50%
Urban,
10%
Construction,
20%
Farm,
20%
Forest
3.
High
Urbanization
75%
Urban,
10%
Construction,
7.5%
Farm,
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
4­
4
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
High
Effectiveness
Estimates
Low
Effectiveness
Estimates
Option
1
Option
2
Option
1
Option
2
1.
Low
Urbanization
348
489
116
466
2.
Moderate
Urbanization
258
363
86
346
3.
High
Urbanization
205
289
68
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
predevelopment
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
4­
5
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
5­
1
Section
5
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D.
and
J
Woodward.
1995.
"Tracing
Sources
of
Suspended
Sediment
in
River
Basins:
A
Case
Study
of
the
River
Culm,
Devon,
UK"
Marine
and
Freshwater
Research.
46:
324­
226.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
5­
9
Waschbusch
et
al.
2000.
"Sources
of
Phosphorus
in
Stormwater
and
Street
Dirt
from
Two
Urban
Residential
Basins
in
Madison,
Wisconsin,
1994­
1995."
In:
National
Conference
on
Tools
for
Urban
Water
Resource
Management
and
Protection.
US
EPA
February
2000:
pp.
15­
55.

Woodward­
Clyde
Consultants.
1992.
Source
Identification
and
Control
Report.
Prepared
for
the
Santa
Clara
Valley
Nonpoint
Source
Control
Program.
Oakland,
California.

York
J.
H.
and
W.
J.
Herb.
1978.
Effects
of
Urbanization
and
Streamflow
Sediment
Transport
in
Rock
Creek
and
Anacostia
River
Basins.
Montgomery
County,
MD,
1972­
1974.
U.
S.
Geological
Survey
Professional
Paper
No.
1003.
72
pp.
Appendix
A
Evaluating
Pollutant
Loadings
from
Construction
Activities
that
Potentially
Impact
the
Environment
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
A­
1
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
II
NPDES
storm
water
rule
economic
analysis
(USEPA,
1999)
presented
information
on
the
size
and
nature
of
construction
activities
under
the
Phase
I
and
II
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
I
NPDES
storm
water
programs.
In
addition,
new
regulations
will
shape
future
development
of
construction
programs
expected
under
the
Phase
II
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
II
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
1
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
1
may
indicate
that
a
construction
program
was
not
evaluated
by
EPA.
Overall,
the
results
in
Table
A­
1
were
converted
into
a
ecoregion
"score"
or
the
percent
of
developed
acreage
that
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
A­
2
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
optionlevel
BMPs
for
approximately
30­
35
percent
of
the
acreage
developed
annually.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
A­
3
Table
A­
1.
Assessment
of
State
Construction
Control
Programs
State/
Territory
Minimum
of
3600
Cubic
Feet
per
Acre
Storage
Requirement
for
Larger
Sites
14­
Day
or
More
Inspection
Frequency
14­
Day
Cover
Required
States
with
Less
than
20
Inches
of
Precipitation
Per
Year
Alabama
Alaska
Yes
Yes
Yes
Arizona
Yes
Yes
Yes
Yes
Arkansas
California
Yes
Yes
Yes
Colorado
Yes
Connecticut
Yes
Yes
Yes
Delaware
Yes
Yes
Yes
District
of
Columbia
Florida
Georgia
Hawaii
Idaho
Yes
Illinois
Yes
Indiana
Iowa
Yes
Yes
Yes
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Yes
Yes
Yes
Michigan
Minnesota
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
State/
Territory
Minimum
of
3600
Cubic
Feet
per
Acre
Storage
Requirement
for
Larger
Sites
14­
Day
or
More
Inspection
Frequency
14­
Day
Cover
Required
States
with
Less
than
20
Inches
of
Precipitation
Per
Year
June
2002
A­
4
Mississippi
Missouri
Montana
Yes
Yes
Nebraska
Nevada
Yes
New
Hampshire
Yes
Yes
Yes
New
Jersey
New
Mexico
Yes
Yes
Yes
Yes
New
York
North
Carolina
North
Dakota
Yes
Ohio
Yes
Yes
Oklahoma
Yes
Oregon
Pennsylvania
Yes
Yes
Yes
Rhode
Island
South
Carolina
Yes
Yes
Yes
South
Dakota
Yes
Yes
Yes
Yes
Tennessee
Yes
Yes
Yes
Texas
Yes
Yes
Yes
Utah
Yes
Yes
Yes
Yes
Vermont
Virginia
Yes
Yes
Yes
Washington
West
Virginia
Yes
Yes
Wisconsin
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
State/
Territory
Minimum
of
3600
Cubic
Feet
per
Acre
Storage
Requirement
for
Larger
Sites
14­
Day
or
More
Inspection
Frequency
14­
Day
Cover
Required
States
with
Less
than
20
Inches
of
Precipitation
Per
Year
June
2002
A­
5
Wyoming
Yes
Yes
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
A­
6
Table
A­
2.
Percentage
of
Acreage
Developed
Without
Option
Equivalent
Requirements
Ecoregion
3600
Cubic
Feet
per
Acre
Storage
in
Sedimentation
Basins
for
Larger
Sites
(Criterion
1)
Certification
of
Sediment
Basins
(Criterion
2)
14­
Day
or
more
frequent
inspection
(Criterion
3)
14­
Day
Cover
For
Wet­
States,
or
none
required
for
dry
states
(Criterion
4)
Overall
Weighted
Percentage
of
Acres
Without
Coverage
ER
1
28.96%
0.00%
28.25%
30.72%
24.7%

ER
2
39.16%
0.00%
57.61%
57.61%
47.1%

ER
3
0.00%
0.00%
10.66%
10.66%
8.0%

ER
4
77.06%
0.00%
77.06%
77.06%
65.5%

ER
5
65.74%
0.00%
65.74%
65.74%
55.9%

ER
6
100.00%
0.00%
100.00%
100.00%
85.0%

ER
7
100.00%
0.00%
100.00%
100.00%
85.0%

ER
8
64.45%
0.00%
68.16%
64.45%
56.6%

ER
9
50.16%
0.00%
55.30%
42.80%
43.4%

ER
10
74.51%
0.00%
81.79%
81.79%
68.8%

ER
11
71.53%
0.00%
71.70%
71.70%
60.9%

ER
12
51.80%
0.00%
65.17%
65.17%
54.1%

ER
13
89.38%
0.00%
32.32%
89.38%
47.4%

ER
14
67.34%
0.00%
53.83%
71.01%
51.4%

ER
15
62.15%
0.00%
100.00%
100.00%
81.2%

ER
16
5.65%
0.00%
100.00%
100.00%
75.6%

ER
17
100.00%
0.00%
100.00%
100.00%
85.0%

ER
18
100.00%
0.00%
100.00%
100.00%
85.0%

ER
19
100.00%
0.00%
100.00%
100.00%
85.0%

National
Average
Weighted
by
Land
Developed
64%
0%
70%
69%
58.9%
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
A­
7
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.
Appendix
B
Inventorying
of
Streams
Potentially
Impacted
By
Construction
Activities
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
1
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
1)
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
1
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
2
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
1.
Regions
for
Stream
Inventorying
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
3




	



	

	

	





		


	

	












	


	






	
	

	



	


	





	

	
	







	

	


	
	











Region
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
Ecoregion
Boundary
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
4
°
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
1:
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
1:
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
network—
one
based
on
1:
2,400­
scale
maps
(a
scale
commonly
used
by
local
governments)
that
includes
the
smallest
swales—
can
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
1:
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
5
0.
9
0
0.
9
1.
8
2.
7
Miles
S
N
E
W
Swal
e
=
1:
24,
0
00
EPA
R
F3
=
1:
100,
000
Stream
Network
Scale
EPA
R
F1
=
1:
250,
000
Figure
B­
3.
Stream
Networks
for
1:
250,000­,
1:
100,000­,
and
1:
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
B­
6
microcomputer
environment
only
when
divided
into
20
separate
parts.
Therefore,
EPA
assumed
that
a
national
dataset
containing
all
streams
and
swales
identifiable
from
1:
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
1:
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.
Appendix
C
Impacts
of
Construction
Activities
on
Hydrology
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
1
The
Soil
Conservation
Service
(SCS)
is
the
former
name
of
the
Natural
Resources
Conservation
Service
(NRCS).

June
2002
C­
1
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
USDA/
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
SCS
1
type
II
rainfall
event,
totaling
3.2
inches
of
rainfall,
was
used
to
conservatively
estimate
the
runoff
hydrographs.

Multiple
land
use
conditions
(Table
C­
1)
were
evaluated
to
help
assess
the
hydrologic
impacts
for
the
small
10­
acre
site.
EPA
notes
that
most
construction
sites
occupying
10
acres
are
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
C­
2
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
1.

Table
C­
1.
Evaluated
Hydrologic
Conditions
for
a
Typical
10­
Acre
Site
Land
Use
Condition
Description
1
Pre­
development:
a
forested
land
use
2
Construction:
cleared
and
grubbed
soil
surface
with
no
vegetation
and
without
construction
runoff
BMPs
(No
sedimentation
ponds)

3
Construction:
cleared
and
grubbed
soil
surface
with
no
vegetation
with
storm
water
BMPs
(a
sedimentation
pond
that
also
shaves
the
peak
runoff
to
match
the
predevelopment
peak
flow)

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
1
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.
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
C­
3
Comparison
of
Various
Construction
Conditions
for
A
Ten
Acre
Construction
Site
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
10
12
14
16
18
20
Time
In
Hours
Flow
Discharged
(cubic
feet
per
second)
Forested
Construction
Site
Without
BMPs
Construction
Site
With
BMPs
Figure
C­
1.
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
Environmental
Assessment
of
Construction
and
Development
Proposed
Effluent
Guidelines
June
2002
C­
4
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
Hours
of
flow
equal
to
or
greater
than:

3
cfs
2
cfs
1
cfs
Forested
0.2
0.3
0.8
Construction
site
without
peak
shaving
BMPs
0.9
1.4
3.3
Construction
site
with
peak
shaving
BMPs
3.2
4
5.7
cfs
=
cubic
feet
per
second
