United State* Offlo* of Water EPA841-R-92-001
Environmental Protection Washington, DC 20460 Juno 1992
Ag«ney
EPA ENVIRONMENTAL IMPACTS OF
STORMWATER
DISCHARGES
A National Profile
-------
CONTENTS
Environmental Impacts
of Stormwater Discharges
Introduction
Stormwater Pollution -
A National Concern
Defining the Problem
A National Ranking
Regulating the Risk
Stormwater and the Urbanization
Process
Pollutants in Stormwater
and Examples of Associated Impacts
Sediment/Habitat Alteration
Oxygen Demanding Substances
Nutrients
Toxic Substances
Bacteria
Floatables
Examples of Successful
Stormwater Controls
Control Practices
Land Disturbance/Activity
Additional Examples of
Successful Urban and Industrial
Stormwater Control Practices
References
inted on Recycled Paper
-------
ENVIRONMENTAL IMPACTS OF
STORMWATER DISCHARGES
Introduction
What constitutes stormwater dis-
charges? What pollutants are asso-
ciated with stormwater and why?
In comparison to other pollution
sources, how does stormwater af-
fect the Nation's rivers, lakes, and
estuaries? What sources of
stormwater pollution are not cur-
rently regulated under the NPDES
program and what are their im-
pacts? What have we learned in
our efforts to control and manage
sources of stormwater pollution?
These questions and others face
local, state, and federal water qual-
ity managers as they struggle to im-
plement cost effective control strat-
egies which target stormwater and
other pollutant discharges in areas
where the greatest risks to water
quality impairment exist. This
booklet was prepared based on the
best available current information,
to assist managers in answering the
above questions. It is intended as a
capsule summary of national level
information on water quality drawn
from various EPA program reports
(i.e., the Section 305(b) National
Water Quality Inventory, the Sec-
tion 319 Nonpoint Source Program,
and the Nationwide Urban Runoff
Program - NURP), as well as from
more site-specific information and
data generated by local agencies
and researchers over the last decade.
The remainder of this booklet is in
three parts. In the first part, we de-
fine the general nature of and im-
pacts from stormwater discharges
and compare, on a national scale,
stormwater pollution to other point
and nonpoint pollution sources. A
differentiation is made between
stormwater discharges that are cur-
rently regulated versus not regu-
lated under the NPDES program.
A discussion of the relationship be-
tween land use/land disturbance
and the magnitude of stormwater
pollution is provided.
In the second part we examine in
more detail, the pollutant character-
istics and impacts of stormwater
runoff. This is presented by a se-
ries of site specific examples where
environmental impacts caused by
various types of stormwater
sources have been observed and
documented.
In the third and last part, we exam^
ine lessons learned from recently
implemented stormwater control
strategies which have shown prom-
ise in effectively minimizing im-
pacts in areas of greatest risk.
,
I '- ./ C-^tk^r1
& - '<:, ;*».'>*:
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STORMWATER POLLUTION -
A NATIONAL CONCERN
Defining the Problem
As human activities alter the water-
shed landscape, adverse impacts to
receiving waters may result from
changes in the quantity and quality
of stormwater runoff. Rain (and
snow) falling onto the surface of
unmanaged urbanizing watersheds
results in a predictable increase in
the quantity of runoff (and snow-
melt) volume flowing to receiving
waters. If left unmanaged, the hy-
draulic impacts (e.g., flooding, ero-
sion, channelization) associated
with the increased water volumes
may be several orders of magnitude
higher than that of the undisturbed
atershed. In addition to causing
noff volume impacts, stormwater
can also be a major nonpoint pollu-
tion source in many watersheds,
which is the focus of the remainder
of this booklet.
There are six primary nonpoint
source activities associated with
stormwater runoff pollution.
They are (in no particular order):
Agriculture,
Silviculture,
Mining,
Construction,
Urban activities,
(including storm sewers, in-
dustrial and commercial oper-
ations, urban growth, land
disposal3, and hydromodi-
fication3), and
Atmospheric deposition.
Table 1. Examples of Pollutant Characteristics Found In Stormwater Runoff
from Various Land Uses In the Great Lakes Region*
Land Use
General Agriculture
Cropland
Improved Pasture
Forested/Wooded
Idle/perennial
General Urban
Residential
Commercial
Industrial
Developing Urban
Suspended
Sediment
(kg/ha-yr)
5-8000
30-7500
50-90
2-900
9-900
300-2500
900-4000
75-1000
750-2000
>10,000b
Total
Nitrogen
(kg/ha-yr)
0.8-75
6-60
5-15
1-8
0.6-7
8-10
6-9
3-12
3-13
90b
Total
Phosphorus
(kg/ha-yr)
0.1-9
0.3-7
0.1-0.6
0.03-0.7
0.03-0.7
0.5-4
0.6-1
0.09-0.9
0.9-6
>10b
Lead
(ka/ha-yr)
0.003-0.09
0.006-
0.007
0.005-0.02
0.01-0.05
0.01-0.05
0.2-0.6
0.08b
0.3-1.0
c
3.0-7.0
\
"Source: Novotny and Chester*, 1981
Only one value reported.
c Not assumed.
The first five are the traditional
nonpoint sources; the sixth, atmo-
spheric deposition, has also been
recognized as a major contributor
of nitrogen, sulfates, and trace met-
als to stormwater runoff in highly
urbanized areas (Halverson, et al.,
1984).
The types and amounts of pollu-
tants carried by stormwater run-
off, commonly resulting in non-
point source pollution of receiv-
ing waters, are highly variable
(USEPA, 1983a). The pollutant
characteristics of stormwater runoff
are largely based on land use char-
acteristics (as illustrated in Table 1)
and vary with the duration and the
intensity of rainfall events (Metro-
politan Washington Council of Gov-
ernments, 1980). Table 1 illustrates
the high variability of pollutant
loads associated with stormwater
runoff. For example, Table 1
shows loads of suspended sediment
vary considerably within a land use
and among land uses. Pollutant
characteristics from stormwater run-
off also vary regionally.
Recent regulatory efforts have fo-
cused almost exclusively on point
sources (e.g., municipal and indus-
trial wastewater discharges). In the
early 1970s, however, it was recog-
nized that nonpoint sources, includ-
ing pollutants originating from agri-
*An undefined portion of land disposal and hydwmodification activities occurs in rural areas.
-------
Table 2(a)
Do not
Support Uses
Partially
Support Uses
Threatened
Fully
Support Uses
Assessed
Total in U.S."
'Not including Great
"Total waters based
Nonpoint Source Ass
1990 State reported
Territories.
. Degree of Designated Use Support in the Nation's
Assessed Waters"
River Lake Estuary
Miles Acres* Square Miles
9.5% (62,21 8)
21% (134,472)
6.5% (43,214}
63% (407,162)
21% (3,940,277)
19% (3,471 ,633)
16% (2,902,809)
44% (8,1 73,917)
8% (2,064)
25% (6,573)
11% (3,052)
56% (15,004)
647,066 18,488,636 26,693
1,800.000 39,400,000 35,624
Lakes
on State-reported Information in America's Clean Water. The States'
essment, ASIWPCA, 1985. Total U.S. estuarine square miles based on
305(b) data and excludes Alaska, New Jersey, Pennsylvania, and Island
319(a)]. These reports contain na-
tional statistics on the degree of im-
pairment of assessed waters [see
Table 2(a) ]. Impairment is mea-
sured according to the level at
which the designated uses of the
waterbody are attained or sup-
ported [see Table 2(b)]. For exam-
ple, as shown in Table 2(a), of the
waters assessed by the States under
305(b) (approximately one-third of
"Source: National Water Quality Inventory: 1990 Report to Congress
culture, mining, and land disposal
activities, as well as stormwater
from diffuse urban sources such as
construction sites, impervious sur-
faces, and unsewered residential
areas, were contributing signifi-
cantly to the impairment of the
Nation's surface and ground waters.
A National Ranking
Based in part on national assess-
ments conducted by the U.S. En-
vironmental Protection Agency
(EPA) it is now recognized that
nonpoint sources and certain dif-
fuse point sources8 (e.g.,
stormwater discharges) are re-
sponsible for between one-third
to two-thirds of existing and
threatened impairments of the
Nation's waters (USEPA, 199la).
Under Sections 305(b) and 319(a)
of the Clean Water Act, states re-
port to the EPA on the quality of
their rivers, streams, lakes, estuar-
ies, coastal waters, wetlands, and
groundwater. EPA, in turn, pre-
pares summary reports to Congress
called the National Water Quality
Inventory [for 305(b)], and Manag-
ing Nonpoint Source Pollution [for
Pollution Source
Categories Considered
306(b) 319
/ /
/ /
/ /
/ /
/ /
/
/ /
/ /
Agriculture
Silviculture
lining
Construction
Urban Runoff*
Combined Sewers
Land Disposal
HydromcxSficatian
Municipal PtSource
Industrial PtSource
Other*
Unknown
"Urban runoff includes sewered and unsewered
urban areas including industrial and commer-
cial; under 319 also includes combined sewers.
Table 2(b). Designated uses and
support levels
Wildlife
Fishery
Shellfishery
Drinking
Agriculture
Industry
Recreation
Navigation
High Quality
Supported
Partial Support
Non-support
Threatened
Msn & wiiairre
Warm water fishery
Cold water fishery
Shellfish protection
Domestic water supply
Agriculture
Irrigation
Livestock watering
Industrial
Recreation
Primary contact
Secondary contact
Noncontact
Navigation
High Quality/
Nondegradation
= all uses supported
= one use not
supported
= 2 or more uses
not supported
= all uses supported
but one or more
uses threatened
Other includes atmospheric deposition, star-
age/lank leaks, highway runoff, spills, in-place,
natural, recreational and urban growth.
Pollutant Categories Considered
(togmd to Figure 1)
305(b) 319
unknown toxictty /
pesticides / /
priority organic* /
nonpriorityorganlcs /
metals S /
ammonia /
chlorine /
other Inorganic* /
ni tfpi0ntA */ ./
nuirivnui * *
pH / /
sBtation / /
organic enrichment/00 / /
salinity / /
thermal modification / /
flow alteration / /
other habitat attentions / /
pathogens . / /
radiation /
oil and grease /
not reported /
suspended solids /
a//i this repon, point sources are pollutant loads discharged at a specific location from pipes, outfalls,
and conveyance channels (ditches, grass swales) from either municipal/industrial wastewater treatment
facilities or from urban, suburban, or industrial/commercial stormwater drainage systems.
-------
Urban
(4%)
Hydromod
(6%)
Mining
(8%)
Natural
(8%)
Silviculture
Others <3%>
(3%)
Construction
(2%)
RIVERS
Silviculture
(9%)
Land Construction
Disposal (6%)
(4%)
Agriculture
(41)
Storm
Sewers/Runotl
(11%)
Hydromod
Unknown
(23%)
Agriculture
(61%)
Mining
(14%)
Combin
Sewers
(2%)
Section 319
1989
Industrial Point S. Municipal Pom! S.
(8%) (16%)
Section 305(b)*
1990
Figure J(a). Comparison of sources impacting use support in rivers.
(see inset previous page for pollution source categories)
*305(b) sou rces may overlap as cause of impairment for a given waterbody,
accounting/or total pie percentage of147%
RIVERS
Flow/Habitat
(4%)
Org. Enr./DO
(5%)
Others
(5%)
Pesticides
(7%)
Org. Enr./DO
(26%)
Flow/Habitat pH Salinity
<«*> <5*> (12%) ^7
(5%)
Siltation
(38%)
Pesticides
(11%)
Pathogens
(8%)
Section 319
1989
Nutrients
(15%)
Pathogens
(19%)
Flow Alteratior
(8%)
Suspended
Solids
(11%)
Siltation
(36%)
Nutrients
(28%)
Section 305(b)*
1990
Figure l(b). Comparison of pollutants impacting use support in rivers.
(see inset previous page for pollutant categories)
*305(b) pollutants may overlap as cause of impairment for a given water-
body, accounting for total pie percentage of 787%.
river miles, one-half of lake acres
and three-quarters of estuarine wa-
ters), roughly 50 to 60 percent are
fully supporting the uses for which
they are designated.
Although methodologies used by
the states to report and analyze data
, differ between the 319 and 305(b)
reports according to the different re-
quirements of the Clean Water Act,
their general conclusions are none-
theless comparable. Both methods,
for instance, use similar pollution
source categories and pollutant cat-
egories (see insets previous page)
to track the relative causes of use
impairment. Figure 1 compares,
for example, the reported pollution
sources and pollutants impacting
use support in rivers for the two
methods. Note that, for rivers,
both the 319 and 305(b) methods
show agriculture to be the pri-
mary source contributing to use
impairment; siltation/suspended
solids and nutrients are the pri-
-------
mary pollutants causing riverine
impacts, followed by pathogens,
metals, and pesticides. Other
nonpoint pollution sources contrib-
uting to use impairment in rivers posal, silviculture, urban run-
and whose individual levels of con- ofl7storm sewers, hydromodification,
tribution are similar for both 305(b) and mining. A major uncertainty is the
and 319 are construction, land dis-
Table 3. Pollution Sources - Regulating the Risk (a comparison of pollution sources
contributing to the Nation's surface water impairment)
% Impairment b Currently Currently
Rivers Lakes Estuaries Regulated Not Regulated
Pollution Source Category8 305(b) 319 30S(b) 319 305(b) 319 Under NPDES Under NPDES
Rural Nonpoint Sources:
Agriculture0
Mining
Silviculture
Subtotal
Urban Nonpont Sources:
Storm Sewers/Urban Runoff
Combined Sewers
Hydro/Habitat Modification*1
Land Disposal4
Construction
Others6
Subtotal
Point Sources:
Municipal Point Sources
Industrial Point Sources
Subtotal
Other Sources:
61 41
14 8
9 3
^i f (
57 23
9 7
3 ^
69 30
18 7
2 &
__2 ._\
22 13
11 4
2
15 6
4 3
6 2
_= 3
38 18
28 6
0
40 6
24 4
3 2
_=: 16
( J.--I-L, f
30 11
&
5
19 8
11
== 43
mi'B'
16
_a _=
25
17
_9 _=
26
3&
_!2 j=
45
only large feed lots all other including ag.
storm and return flows
only sites > 2 ha (5 ac) all sites < 2ha (5 ac)
/
industrial sites and all cities and counties
cities and counties with with pop. < 100,000
pop. 2 100,000
f
/
all but septic tanks septic tanks
only sites > 2ha (Sac) all sites < 2ha (Sac)
/
/
Unknown 23 21 4 ? ?
Natural6 8 10 5 /
In-place6
Total Percent
3 16
147 100
190 100
138 100
/
"b See explanation of pollution sources on next page.
Percent of impaired river miles, lake acres, and estuary square miles affected by each pollution source.
c See 319 agriculture breakdown on next page.
An undefined portion of use impairment from hydro/habitat modification and land disposal is attributable to rural areas resulting in an
overestimation of urban contribution to impairment.
' others include, in addition to natural and m-place .atmospheric deposition, waste storage/storage tank leaks, highway maintenance and
runoff, spills, recreational activities, and urban growth.
'Box indicates largest contributor to use impairment by category group (i.e., rural nonpoint, urban nonpoint, point, or other).
-------
Agriculture
Nonirrigated crops
Irrigated crops
Specialty crops
Pastureland
Rangeland
Feedlots all types
Aquaculture
Animal Holding areas
Streambank erosion
Unspecified/odd
Total
Subcategorles Under 319"
Rivers
(miles)
5.7
1.9
0.1
1.4
2.1
2.4
0.0
1-4
0.7
25.2
41.0
(legend to Table 3)
% Impairment
Lakes
(acres)
2.3
3.8
0.4
0.9
0.5
0.7
0.0
0.7
0.1
13.7
23.0
Estuaries
(Sq. miles)
0.3
0.0
0.0
0.6
0.8
0.1
0.0
0.4
0.0
_4£_
7.0
"Source: Managing Nonpoint Source Pollution: 1991 Report to Congress
23% unknown sources identified in
the 319 program for rivers.
Table 3 extends the comparison be-
tween 319 and 305(b) methods for
pollution sources causing impair-
ment of assessed river miles, lake
acres (excluding Great Lakes) and
estuary square miles, as reported in
the most recent 305(b) document
(USEPA, 1992), and 319 document
(USEPA, 1991a). Pollution source
categories are grouped into rural
nonpoint sources, urban nonpoint
sources, point sources, and other
sources. As seen in Table 3, the
level of contribution to reported im-
pairment caused by a given 319 or
305(b) source category varies be-
tween waterbody types, however,
the general trend is similar for both
methods. For example, for rivers,
rural nonpoint sources represent the
largest contribution to impairment
under both 319 and 305(b) meth-
ods, followed by urban nonpoint
sources. For lakes and estuaries,
however, the largest contributors
to use impairment are reported
to be urban nonpoint sources, re-
gardless of which method is used.
Stormwater runoff from agricul-
ture and from urban areas are
the two present leading causes of
surface water quality impairment
nationwide, except for estuaries
(where point sources are shown to be
the second largest contributor to im-
pairment behind urban nonpoint
sources)
Furthermore, while urban population
areas (greater than 2500 inhabitants
as defined by the Bureau of Census)
take up only about 2.5% of the total
land surface of the country, stormwa-
ter pollution from these urban areas
and associated urban activities (i.e.,
storm sewers/urban runoff, combined
sewers, hydromodification, land dis-
posal, construction, urban growth,
etc.) accounts for a proportionately
high degree of wateFquality impair-
ment (i.e., 18% of impaired river
miles, 34% of impaired lake acres,
and 62% of impaired estuary square
miles reported under 319) when com-
pared to that (see Table 3) from rural
activities (i.e., agriculture, silvicul-
ture, and mining) which take up ap-
proximately 53% of the total land
surface (USDA, 1992).
Explanation of 305(by3l9 Pollution Sources (legend to Table 3}
Agriculture:
Silviculture:
Runoff from crop production, pastures, rangetand, feedlots,
and irrigated return flows
Runoff 1rom forest management, harvesting, and road
construction
Mining:
Construction:
Urban Runoff:
Combined Sewers:
Land Disposal:
Hydromodification:
Municipal Point Source:
Industrial Point Source:
Other
Unknown:
Runoff and process fluids from mining, petroleum drilling, and
mine tailing sites
Runoff from highway building and land development
Runoff from sewered and unsewered unban areas, including
industrial and commercial activities; under 319 also includes
combined sewers
Storm and sanitary sewers combined, which may discharge
untreated wastes during storms
Runoff and leachate from landfills, septic tanks, and
hazardous waste disposal sites
Channelization, dredging, dam construction, and streambank
modification
Discharge from POTW (publicly owned treatment works)
Discharge from industrial processes
Includes atmospheric deposition, waste storage/tank leaks,
highway runoff, spills, in-place contaminants, natural, and
recreational and urban growth
Unknown
-------
This indicates the importance of
focusing efforts on the manage-
ment and control of stormwater
discharges from urban areas and
associated urban activities (i.e.,
storm sewers/urban runoff, com-
bined sewers, hydromodification,
land disposal, construction,
urban growth, etc.) since the po-
tential for future urban growth
and cumulative impacts from in-
creased stormwater discharges
from expanding urban activities
is relatively great.
The above analysis, although an
approximation, indicates the rela-
tive importance of urban stormwa-
ter discharges as a major contribu-
tor to the impairment of the
Nation's waters. This is consistent
with the National Oceanic and At-
mospheric Administration (NOAA)
findings that urban runoff is a lead-
ing cause of impairment to shell-
fish growing waters (NOAA; 1988;
1989; 1990). This qualitative anal-
ysis does not allow, however, for a
detailed ranking of all subcategor-
ies of stormwater discharges, in-
cluding industrial and commercial
activities occurring in urban areas.
Certain source categories included
under 319 and 305(b) that do corre-
late well with industrial activities
are land disposal, mining, and con-
struction and these are shown to be
important contributors to water
quality impairment (see Table 3).
It is not readily apparent as to what
degree stormwater discharges are
currently regulated in relation to
the level of impairment reported.
For example, although agriculture
is a major nonpoint source contribu-
tor to water quality impairment,
currently only the largest animal
feedlots require stormwater dis-
charge permits. Table 3 shows the
status of National Pollutant Dis-
charge Elimination System
(NPDES) permit requirements for
each pollution source category and
we discuss this status in more detail
below.
Regulating the Risk
The 1987 amendments to the Clean
Water Act require EPA to develop
NPDES permit application require-
ments for the following "Phase I"
classes of stormwater discharges:
discharges from large munici-
pal separate storm sewer sys-
tems (systems serving a popu-
lation of 250,000 or more) and
medium municipal separate
storm sewer systems (systems
serving a population of
100,000 or more, but less than
250,000);
stormwater discharges associ-
ated with industrial activity
[identified by Standard Indus-
trial Classification (SIC)
codes]; and
discharges which are desig-
nated by EPA or an NPDES
approved State as needing an
NPDES permit because the
discharge contributes to a vio-
lation of a water quality stan-
dard or is a significant con-
tributor of pollutants to wa-
ters of the United States.
Statutorily excluded from the
NPDES requirements under the
Clean Water Act are general agricul-
tural stormwater, irrigation return
flows, and uncontaminated runoff
from oil and gas or mining opera-
tions.
The CWA creates a temporary mor-
atorium on the general requirement
of the CWA that point source dis-
charges of pollutants to waters of
the United States must be author-
ized by an NPDES permit. Under
the moratorium, EPA is prohibited
from issuing NPDES permits for
non-Phase I discharges composed
entirely of stormwater prior to Oc-
tober 1, 1992. EPA is required to
issue regulations by no later than
October 1,1992 which designate
additional "Phase II" stormwater
discharges to be regulated to pro-
tect water quality and establish a
comprehensive program to regulate
such designated sources. The pro-
gram must, at a minimum:
(A) establish priorities,
(B) establish requirements for State
stormwater management programs,
and
(C) establish expeditious deadlines.
The program may include perfor-
mance standards, guidelines, guid-
ance, and management practices
and treatment requirements, as ap-
propriate.
Phase I Stormwater Discharges.
On November 16,1990, EPA pub-
lished regulations specifying per-
mit application requirements for in-
dustrial activities and large/medium
municipal separate storm sewer sys-
tems, the two major classes of
Phase I stormwater sources (see
inset next page).
Municipal - The November 16,
1990 regulations defined a mu-
nicipal separate storm sewer sys-
tem serving a population of
100,000 or more to include mu-
nicipal separate storm sewers
within the boundaries of 173 in-
corporated cities, and within un-
incorporated portions of 47
counties that were identified as
-------
Defining Stormwater
Discharges
As "Phase I' Discharges:
Municipal:
> Separate storm sewers8 in incor-
ited (city) and unincorporated
ty) urban areas with popula-
r 100,000 or more
> CornWned sewer overflows (sub-
ject to NPDES permit require-
ments prior to Phase i)
industrial:
Heavy manufacturing facilities
Medium manufacturl
with materials e
facilities
to rainfall
> Priority oH and gas facilities
> Active and inactive mines
>- Construction sites greater than
2ha(5ac)
> Landfills, storage or disposal facil-
ities handling industrial/hazard-
ous wastes
> Scrapyards/salvage yards
> Runoff from sewage treatment
plants
> Selected transportation facilities
> Steam electric power plants
> Large animal feedlots (subject to
NPDES permit requirements prior
to Phase I)
Statutory Excluded:
> Agricultural stormwater
> Irrigation return flows
> "Uncontaminated" runoff from
08 and gas or mining opera-
tions
"Separate storm sewers include pipe
conveyance as well as ditches, and grass
swales in suburban areas
having populations of 100,000 or
more in unincorporated. Urbanized
portions of the county. In addition,
the regulations allowed for addi-
tional municipal separate storm
sewers to be designated by the Di-
rector of the NPDES program as
being part of a large or medium mu-
nicipal system. The inclusion of
these 173 cities and 47 urban
counties in the Phase I program
recognizes that stormwater run-
off from high density urbanized
areas has a significant potential
to impact receiving waters due to
the greater concentration of com-
mercial and industrial activities; the
existence of leaks, cross connec-
tions and illicit discharges into
sewer systems; and the large im-
pervious areas which normally
exist.
Industrial - The November 16,
1990 regulations also defined the
term "storm water discharges asso-
ciated with industrial activity"
broadly to include 11 categories of
industrial facilities (see Phase I
inset). EPA estimates that over
100,000 industrial facilities are ad-
dressed by this definition. Many of
the Phase I industrial facilities
(e.g., mining, landfills, construc-
tion, etc.) have previously been ad-
dressed by the NPDES program as
traditional sources.
For example, stormwater dis-
charges from mining sites have
long been recognized as having sig-
nificant impacts on receiving water
quality, and national effluent guide-
line limitations under NPDES have
been developed for most types of
mining activities to control surface
drainage (but not groundwater seep-
age). A wide variety of waste mate-
rials can be exposed to stormwater
at waste disposal sites and scrap
yards, which now require NPDES
permits. Under RCRA Subtitle D,
States reported that of the 1,100
municipal solid waste landfills
which monitored discharges to sur-
face water, 660 were cited for sur-
face water impacts. Older landfills
are of most concern because they
may have received large volumes
of hazardous waste and, in general,
their use of design controls was
very limited. Runoff generated
from construction activities has the
potential for serious water quality
impacts from sediments and other
land related pollutants. Annually,
about 1.6 million acres of land are
disturbed by construction activities
nationwide. Only construction
sites larger than 5 acres are cur-
rently required to be permitted
under NPDES.
Pollutant concentrations in run-
off from industrial facilities lo-
cated in urban areas can be sig-
nificantly higher than from resi-
dential or commercial areas due
to the increased presence and
amounts of toxic materials (Roes-
ner, 1978). In general, the level of
pollutants from industrial facilities
is related to the type of activities oc-
curring at the site, and the degree to
which these activities are exposed
to precipitation. Illicit connections,
cross connections, improper waste
disposal, and spills may also con-
tribute sanitary or industrial waste
waters directly to municipal storm
sewer systems, leading to high
metal, nutrient, or bacterial concen-
trations. A high priority has been
set under the Phase I NPDES
stormwater permit program to iden-
tify and bring these "non-storm"
water pollution discharges under
control.
-------
Phase I Implementation The
Phase I stormwater program takes
two very different approaches to de-
fining the roles of EPA and author-
ized NPDES States in controlling
pollutants in stormwater dis-
charges. With respect to permits
for large and medium municipal
systems, the efforts of the NPDES
permitting authority (EPA or an au-
thorized NPDES State) are directed
to ensuring that municipalities de-
velop and implement stormwater
management programs to control
pollutants to the maximum extent
practicable. Municipal programs
address ways to reduce pollutants
in stormwater from privately-
owned lands (e.g., commercial op-
erations, houses) that discharge to a
municipal system, as well as modi-
fying municipal activities (e.g.,
road deicing and maintenance,
flood control efforts, maintenance
of municipal lands, etc.) to address
stormwater quality concerns.
NPDES permit activities can define
the role of municipalities under this
program in a flexible manner that
allows local governments to assist
in identifying individual priority
pollutant sources (e.g., industrial
sources, illicit connections, spills,
etc.) within the municipality and to
develop and implement appropriate
controls for such discharges.
With respect to permits for
stormwater discharges associated
with specific Phase I industries
identified in the November 1990
regulations, the NPDES permitting
authority has a more direct role in
regulating these facilities. In addi-
tion, NPDES permits for dis-
charges from large and medium mu-
nicipal separate storm sewer sys-
tems will establish municipal re-
sponsibilities for assisting EPA and
authorized NPDES States in im-
plementing controls to reduce pollu-
tants in stormwater discharges asso-
ciated with Phase I industrial activi-
ties which discharge through mu-
nicipal systems.
Phase n Stormwater Discharges.
EPA is currently evaluating a num-
ber of options for identifying Phase
II stormwater discharges to be regu-
lated to protect water quality. Of
the options being considered, per-
haps the most difficult to address
is whether to expand the catego-
ries of individual facilities (such
as commercial or light industrial
facilities) requiring permits, or
rather to include these within an
expansion of municipal separate
storm sewer systems requiring
permits. Addressing additional
municipal separate storm sewer sys-
tems would result in requiring the
selected municipalities to:
(A) identify individual priority
pollutant sources within the munici-
pality (e.g., industrial sources,
illicit connections, spills, etc.), and
(B) develop and implement appro-
priate controls for such discharges.
On the other hand, individual facili-
ties specifically identified as new
categories under Phase II of the
NPDES stormwater permit pro-
gram would primarily be regulated
directly through requirements in
NPDES permits. These two classes
of Phase n sources (i.e., individual
and municipal) are discussed in
more detail below.
For individual facilities under
Phase n, EPA could specify new
categories of stormwater discharges
(in addition to the existing 11 cate-
gories) to be regulated separately
or under Phase n municipal sepa-
Defining Stormwater
Discharges
As "Phase II" Discharges:
Municipal:
> Separate storm sewersa in incor-
porated (dry) and unincorporated
(county) urban areas with popula-
tions less than 100,000
Indrviduai facilities:
> industrial facilities owned or oper-
ated by municipalities with a pop-
ulation less than 100,000
x Light industrial facilities
> Medium industrial facilities with-
out materials exposed to rainfall
> Gas stations and automobile re-
lated facilities
> Tank farms
> Abandoned mine sites
> Construction sites less than
2ha(5ac)
> Runoff from construction pro-
jects for roads used for sifvicul-
ture
> Municipal landfills that do not re-
ceive industrial waste
> Large parking lots (shopping cen-
ters, stadiums, etc)
> Military bases
> Research centers
> Animal feedlots not currently sub-
ject to NPOES permit require-
ments
"Separate storm sewers include pipe con-
veyance as well as ditches, and grass
swale in suburban areas
rate storm sewer systems. Among
the discharges that EPA could in-
clude for Phase II requirements are
the 13 categories of stormwater
sources identified in the inset
above. The number of individual
facilities within these new catego-
ries under consideration is cur-
rently unknown.
-------
For municipal separate storm
sewer systems under Phase II,
EPA is considering expanding
NPDES requirements to urban
areas having populations less than
100,000. Under Phase I, EPA de-
fined municipal separate storm
sewer systems on the basis of politi-
cal boundaries, including 173 incor-
porated cities (having a population
of 100,000 or more) and 47 of 500
counties having an unincorporated
urban population of 100,000 or
more. The counties that were ad-
dressed by the 11/16/90 regulation
were in a handful of States, primar-
ily MD, VA, FL, and CA. While
the current regulations indirectly
address suburban growth in
these States, in most parts of the
country, the regulations only ad-
dress core cities and exclude sub-
urban or "urban fringe" develop-
ment. This is typified in Figure 2
for the Milwaukee, Wisconsin area,
where only the incorporated city of
Milwaukee and none of the urban
fringe area within Washington,
Waukesha, Ozaukee, Milwaukee,
and Racine Counties is required to
apply for a stormwater permit. The
1990 population for the Milwaukee
urbanized area is about twice that
of Milwaukee City and population
densities are similar.
The Bureau of Census has defined
396 "urbanized areas" (UAs) based
on the 1990 Census to define large
metropolitan population patterns.
UAs are comprised of a central
"core" city (or cities) with a sur-
rounding closely settled area. The
population of the entire urbanized
area must be greater than 50,000
people, and the closely settled area
outside the city, the urban fringe,
must have a population density gen-
erally greater than 1,000 persons
Table 4.
Size of UA
250,000
or more
100,000-
250,000
50,000-
100,000
Municipalities Associated With Urbanized Areas (UAs)a
Number of
UAs
172
121
103
Number of
Incorporated
3,874
930
829
Number of
Minor Civil
Divisions'
880
362
315
Number of
County
Equivalents
470
200
258
"Based on 1990 Census data
b
Incorporated places include incorporated cities, towns, villages, and boroughs
Minor civil divisions include unincorporated towns and townships in 20 States
County equivalents include counties, parishes in LA, and boroughs in Alaska. Some dou-
ble counting of counties occurredas portions of several UAs may be in one county (for ex-
ample, the portions of the Washington UA, Baltimore UA, and Annapolis UA are in Anne
Arundel County, MD)
per square mile (just over 1.5 per-
sons per acre) to be included.
These 396 UAs contain over 158
million people, or over 63% of
the Nation's total population.
However, UAs only occupy about
1.5-2% of the Nation's land area.
Urban fringe areas surrounding
core cities are typically divided
into numerous local governments,
as defined in Table 4 based on
1990 Census data.
The 220 Phase I NPDES munici-
palities have a combined urban pop-
ulation of 78 million. The remain-
ing 80 million people located in ur-
banized areas are outside of Phase I
municipalities. Most urban
growth occurs in the urban fringe
areas outside of core cities. For ex-
ample, between 1970 and 1980, the
population of incorporated cities
with a population of 100,000 or
more (Phase I cities) increased by
only 0.6 million, with the popula-
tion of many of these cities decreas-
ing. Between 1970 and 1980, the
population of urbanized areas out-
side of cities with a population of
100,000 or more increased 30
times more (an increase of 18.9 mil-
lion) than the population of these
core cities. This is important from
a stormwater perspective as numer-
ous studies (e.g., NURP) have
shown that it is much more cost ef-
fective to develop measures to
prevent or reduce pollutants in
stormwater during new develop-
ment than it is to correct these
problems later on.
Addressing new development is
generally considered to be institu-
tionally feasible as many municipal-
ities already have some form of ap-
proval or permit program in place
that can be modified to address
stormwater concerns. In addition,
the economic achievability of im-
plementing stormwater controls is
expected to be greater for new de-
velopment versus established core
cities since: (1) structural controls
and therefore costs can be mini-
mized; (2) new development often
absorbs a significant portion of in-
frastructure capital costs; and (3)
the tax base on a per capita basis in
urban fringe areas is likely to be
-------
MILWAUKEE URBANIZED AREA
AND MILWAUKEE CITY
POPULATION
1990
1980
URBANIZED
AREA
MILWAUKEE
CITY
1.226,293 1.207.008
628,088 636.212
WASHINGTON CO
WAUKESHA CO
LEGEND
LAKE
MICHIGAN
LIMITS OF URBANIZED
AREA
AREA UNDER NPDES
STORMWATER PERMIT
PROGRAM
Figure 2. Jurisdiction of Phase I NPDES Stormwater Permit Program in Milwaukee, Wisconsin
-------
cASTERN MARYLAND DELAWARE, AND D.C
Couniy to which 6217(g) CZARAapptas
County or Urge auniclpilUy under
NPOES stonmater perntt progrjn
Figure 3. Jursidiclion of Phase I NPDES Stormwater and CZAKA Programs in Maryland, Delaware, and Washington, DC
greater (National League of Cities,
1991).
Relationship of NPDES to Other
Programs. Figure 3 illustrates the
current jurisdiction of the Phase I
NPDES Stormwater discharge per-
mit program and the Coastal Non-
point Pollution Control Program
under Section 6217(g) of the
Coastal Zone Act Reauthorization
Amendments of 1990 (CZARA),
respectively, in Maryland, Dela-
ware, and Washington, DC. Al-
though not a permit program, the
CZARA program is intended to fos-
ter the development and im-
plementation of management mea-
isures for nonpoint source pollution
control to restore and protect
coastal waters in conformance with
guidance developed by EPA
(USEPA, 1991c). "Management
measures" are defined under
CZARA as economically achiev-
able measures to control the addi-
tion of pollutants to coastal waters,
which reflect the greatest degree of
pollutant reduction achievable
through the application of the best
available nonpoint pollution con-
trol practices, technologies, pro-
cesses, siting criteria, operating
methods, or other alternatives.
CZARA management measures in-
clude a mix of non-structural and
structural control practices in order
to optimize costs and pollutant re-
moval effectiveness over a range of
land uses and activities.
For the example presented in Fig-
ure 3, two cities in close proximity
(Washington, DC and Baltimore,
MD) and the urbanized counties
which surround these cities are ad-
dressed by the Phase I NPDES pro-
gram. However, incorporated
towns or cities with populations
less than 100,000 within the
NPDES counties are exempt
from the NPDES program, such
as the city of Annapolis, MD, as
well as 43 other incorporated towns
in Anne Arundel, Prince Georges,
and Montgomery Counties (MD).
Since Maryland is an approved
-------
coastal zone State3, the areas
within the coastal zone that are ex-
empt from NPDES requirements
will be included in the State's ap-
proved Coastal Nonpoint Pollution
Control Program under CZARA.
Counties and municipalities land-
ward of the coastal zone with popu-
lations less than 100,000 are cur-
rently not addressed by either the
Phase I NPDES or CZARA pro-
grams and fall under the jurisdic-
tion of other nonpoint source man-
agement programs including Sec-
tion 319 of the Clean Water Act
and US Department of Agriculture
conservation programs.
8 There are 29 federally approved State
and Territorial coastal zone programs, in-
cluding states bordering the Great Lakes
(e.g., Wisconsin). -The definition of the ap-
proved coastal zone boundary varies sub-
stantially by State.
Stormwater and the Urban-
ization Process
As pointed out by Novotny (1992),
the extent and nature of stormwa-
ter pollution is characterized not
only by rneteorologic conditions,
type of land surface, and its in-
herent difficulty to measure or
quantify, but perhaps most im-
portantly by its relationship to
the level and type of activity, or
disturbance, occurring on the
land surface in question.
In the EPA Nationwide Urban Run-
off Program (NURP), significant
differences in measured pollutant
concentrations, reported as event
mean concentrations (EMCs), were
not detected among the three major
urban land use categories (i.e., resi-
dential, commercial, and mixed
urban). Only open/non-urban lands
were significantly different from
the previous three land use types
Phases of Urbanization
Suburban/Urban Area Development -
Land conversion through deforestation and drainage/filling creates extensive
erosion and changes the hydrologic balance of the watershed. Soil loss from un-
controlled construction can reach a magnitude of over 100 ton/ha.yr. Shifts from
the natural watershed flow and stream channel conditions greatly reduce the
habitat value of the stream.
Suburban/Urban Areas Post Development-
Once stabilized, pollutants accumulate on impervious surfaces and are washed
off. Primary pollutant sources are atmospheric deposition, urban surfaces
(roofs, autos on streets), and miscellaneous activities (animals, fitter, spills, fertil-
izer application, street salting, septic system failures, etc.). Loading rates of pol-
lutants are generally correlated with degree of imperviousness, land area size,
and type of drainage system.
Fully Developed (Core)Urban Areas-
Sewered watersheds are characterized by extensive impervious areas, large run-
off volumes during storms, and increased loadings of pollutants from similar
sources (see above). Older urban areas commonly are served by combined sew-
ers which often overflow during wet weather releasing pathogens and industrial
toxicants. Increased industrial and commercial activities (land disposal, storage
piles, vehicle maintenance, spills, etc.) create opportunities for release of toxic
substances into separate and combined sewer systems.
(USEPA, 1983b). The NURP data
point out the existence of high vari-
ability in urban stormwater runoff
quality and the need to characterize
urban runoff for individual urban
areas when conducting site-spe-
cific designs for stormwater con-
trols. Data on pollutant loadings
given in Table 1 also demonstrate
the wide variations in loads associ-
ated with traditional land use cate-
gories.
In contrast to land use, land distur-
bance through urbanization, (i.e.,
construction, deforestation, wetland
drainage, channelization) is per-
haps more directly correlated to the
level of pollutant loadings and im-
pacts caused by stormwater runoff.
Urbanization alters the natural
vegetation and natural infiltra-
tion characteristics of the water-
shed, causing runoff from an
urban area to have a much
higher surface flow, a much
smaller interflow, and a some-
, what reduced baseflow (see Fig-
ure 4). Urbanization also can cre-
ate water quality impacts by in-
creasing the amount of sediment,
nutrients, metals, and other pollu-
tants associated with land distur-
bance and alteration activities, as
well as with the permanent increase
in the impervious urban surfaces
created . Thus urbanization tends
to increase both runoff volumes
and pollutant loadings to the receiv-
ing waterbody.
Effects of Urbanization-Develop-
ing Areas. The change of land use
from natural or agricultural to
-------
urban occurs in several steps (see
knset previous page) that range
from developing suburban/urban
areas to fully developed cities ser-
viced by extensive sewer networks
and transportation corridors.
During the construction phase of
suburban/urban land development,
the hydrology of a stream changes
in response to initial site clearing
and grading. Trees that had inter-
rupted rainfall are felled (see Fig-
ure 4a). Natural depressions that
temporarily ponded water are
graded to a uniform slope. The
thick humus layer of the forest
floor that had absorbed rainfall is
scraped off or eroded away. Hav-
ing lost much of its natural stor-
age capacity, the cleared and
graded construction site can no
longer prevent rainfall from
being rapidly converted to runoff
.(Schueler, 1987).
Pollutant export increases dramati-
cally both during and after develop-
ment. Unless adequate erosion
controls are installed and main-
tained at the site, enormous quan-
tities of sediment are delivered to
the stream channel, along with at-
tached soil nutrients and organic
matter. Uncontrolled construction
site sediment loads have been re-
ported to be on the order of 35 to
45 tons/acre/year (Novotny and
Chesters, 1981; Wolman and
Schick, 1967; Yorke and Herb,
1976, 1978).
After construction is completed,
roof tops, roads, parking lots, side-
walks, and driveways make much
of the site impervious to rainfall.
Unable to percolate through the
soil, rainfall is converted to runoff.
|The excess runoff becomes too
^great for the existing drainage sys-
a Water Balance
EviDO- *- '
transpiration ;
untrflow Basefto*
b streami
Figure 4. Changes in Watershed Hydrology as a Result of Urbanization (Schueler, 1987)
tern to handle. As a result, the drain-
age network must be improved to di-
rect and convey the runoff away
from the site (Schueler, 1987).
Downstream of the land develop-
ment activity, impacts in the form
of streambank erosion, channeliza-
tion, and elimination/alteration of
habitat occur due to increases in
streamflow volumes, flooding fre-
quency, peak flows, and move-
ment of sediment The effect of de-
velopment on stream hydrology in a
typical, moderately developed water-
shed is shown in Figure 4b,c and
summarized in the inset (next page)
by Schueler (1987),
Construction activities are tempo-
rary, but the permanent change
-------
Changes in Stream Hydrology from Urbanization3
Increased peak discharges compared to predevelopment levels (Leopold, 1968;
Anderson, 1970);
Increased volume of storm runoff produced by each storm in comparison to pre-
development conditions;
Decreased time needed for runoff to reach the stream (Leopold, 1968), particu-
larly if extensive drainage improvements are made;
Increased frequency and severity of flooding;
Reduced streamflow during prolonged periods of dry weather due to the reduced
level of infiltration in the watershed; and
Greater runoff velocity during storms, due to the combined effect of higher peak
discharges, rapid time of concentration and the smoother hydraulic surfaces that
occur as a result of development.
'Schuel£r(1987)
"MWCOG (1983a). Note:
nodata
Table 5. Average Annual Atmospheric Deposition Rates for the
Washington, D.C. Area*
Pollutant Rural (si) Suburban (b) Urban (c)
(Ibs/acre/year)
Total Solids
Chemical Oxygen Demand
Total Nitrogen
Nitrate-N
Ammonia-N
Total Kjeldahl-N
Total Phosphorus
Ortho-phosphorus
Trace Metals
Cadmium
Copper
Lead
Iron
Zinc
99
199
19.9
9.4
5.5
10.5
0.71
0.28
ND
NO
0.06
ND
0.67
155
133
12.8
5.6
1.1
7.2
0.50
0.26
0.09
0.21
0.44
1.57
1.35
245
210
17.0
6.8
1.0
10.2
0.84
0.35
0.003
0.61
0.53
5.60
0.65
in land use and the hydraulic and
pollutant characteristics associ-
ated with the transformed urban
landscape produce lasting effects.
Most of these impacts are caused
by the net increase in impervious
surfaces. In developed subur-
ban/urban areas, pollutants accumu-
late rapidly on impervious surfaces
and are easily washed off. Mea-
sured rates of atmospheric deposi-
tion of pollutants in the Washington
D.C area are summarized in Table
5. Halverson et al. (1984) reported
that the contribution of precipita-
tion to runoff pollution from paved
surfaces was 100% for ammonia
and nitrate nitrogen. They also re-
ported values of 28 percent for sul-
fate and 13 percent for phosphorus.
They suggested that nitrogen, sul-
fate and phosphorus should be con-
sidered when assessing urban run-
off quality. The type of surfaces
in the urban landscape are also
an important source of pollutants
in runoff. Trace metals, for exam-
ple, are a common component of
surfaces such as roofing materials,
downspouts, galvanized pipes,
metal plating, paints, wood preser-
vatives, catalytic converters, brake
linings, and tires. Over time, these
surfaces corrode, decay, or leach
out, releasing metals into the runoff
(Schueler, 1987). Other sources
of pollutants that accumulate
and subsequently wash off im-
pervious surfaces include pet
droppings, lawn fertilizer and
pesticides,organic matter, litter,
used motor oil, and road salt (see
Table 6).
Gwinnett County, Georgia, An
Urban Fringe Area. Stormwater
runoff characteristics also vary
with the age of the development
and the rate at which natural and ag-
ricultural lands are converted to
urban areas. This rate of change de-
pends on the land location and its
proximity to other urban areas and
core cities. Urban fringe areas
are experiencing the largest land
use changes due to rapid growth
in population resulting in an ex-
cessive net increase in pollution
loadings. Many of these fringe
areas are not currently covered
under the Phase INPDES
Stormwater program. Atypical
rapidly growing fringe area not ini-
tially regulated under the NPDES
program, Gwinnett County, GA
-------
Table 6. Sources of Urban Runoff Pollutants
Source
Erosion
Atmospheric Deposition
Construction Materials
Manufactured Products
Landscape Maintenance
Plants and Animals
Septic Tanks
Non-stormwater Connections
Accidental Spills
Pollutant of Concern
Sediment and attached soil nutrients, organic matter,
and other adsorbed pollutants.
Hydrocarbons emitted from automobiles, dust, aromatic
hydrocarbons, metals, and other chemicals released
from industrial and commercial activities.
Metals from flashing and shingles, gutters and
downspouts, galvanized pipes and metal plating, paint,
and wood preservatives.
Heavy metals; halogenated aliphatics; phthalate
esthers; PAHs; other volatiles; phenols and oil from
automobile use, zinc and cadmium from tire wear, and
pesticides and phenols from other uses including
industrial.
Fertilizer and pesticides. Generally as impervious area
increases, nutrients build up on surfaces and runoff
transport capacities also rise resulting in high loads.
Exceptions include intensively landscaped areas (e.g.,
golf courses, cemeteries).
Plant debris, animal excrement.
Coliform bacteria, nitrogen/NOs
Inadvertent or deliberate discharges of sanitary sewage
and industrial wastewater to storm drainage systems,
including illicit connections, leaking sanitary collection
systems, spills, industrial and commercial activities,
construction activities, infiltration of contaminated
groundwater, and improper disposal.
Pollutants of concern depend on the nature of the spill.
" Based in part on Woodward-Clyde Consultants, 1990.
(see Figure 5) has experienced an
increase in population from about
72,000 to 275,000 during the 1975
to 1986 period, and significant con-
version of forest and agricultural
lands to urban areas. Urban areas
increased from about 50,000 acres
in 1975 to over 100,000 acres in
1990 (Atlanta Regional Commis-
sion land use database - unpub-
lished). This urban fringe growth
rate, although high, was not signifi-
cantly different from that of all
urban areas in the entire country
during this same time period, ac-
cording to Bureau of Census data
(USDA, 1992). Based on analy-
sis of Census data, the projected
population of Gwinnett County is
expected to exceed 700,000 by
year 2012 (also county estimate).
Consequently, the corresponding
increase in urban areas may be ex-
pected to exceed 170,000 acres or
about 300% of the 1975 values.
Gwinnett County
D
Metro Counties. 1970
Metro Counties Added in 1983
Metro Counties Added in 1980
Georgia
Metro AUsnu Figures From: The Georgia County Guide.
1991. The University of Georgia, Cooperative Extension
Service, College of Agriculture, Athens, GA.
Figure 5. Location of Gwinnett County, Georgia
-------
Figure 6a illustrates the observed
(1975-85) and expected (1985-
2012) rate of change in land use dis-
tribution as the population in-
creases.
In the absence of a comprehens-
ive urban planning program ad-
dressing stormwater runoff in
particular, such rapid land con-
version and associated land dis-
turbances due to construction ac-
tivities will yield high sediment
and pollutant loadings. Further-
more, the permanent change in
land use activities will result in
dramatic changes in hydrologic
and pollutant characteristics.
Current NPDES regulations ad-
dress construction activities (>5
acres) but do not address the
longer term cumulative effects of
urbanization.
The long-term rates of change of
nutrient loadings in Gwinnett
county were roughly estimated
using a generalized loading func-
tion model and existing informa-
tion from the Census and National
Resource Inventory files. Nutrient
load estimates were derived for the
years 1975,1980, and 1985 based
on existing land use and population
data, and for the year 2012 based
on projected land use distribution
(Figure 6b). Projected population
and land use distributions for 2012
were estimated based on the mean
annual rate of change during the
1975-1985 period. Temporary sedi-
ment and nutrient loadings due to
construction activities were not con-
sidered in these estimates. Cur-
rently, construction activities are
regulated under Federal or State ap-
proved NPDES programs. The
2012 nutrient loading projections
indicate a relative increase in nitro-
5
M
1975
* Population
a. Projected population growth and changes
in major land uses in Gwinnen County. GA.
2012
Ag/Forest
Urban
to
E.
Ao/Foresl
Urban
b. Projected increase in total runoff nutrient loadings and
changes in land use in Gwinnett County. GA.
1800
1300
800
300
I .
1975
1984
--»- No Control
- -»- Controlled Since 1975
Controlled Since 1992
1993
Year
2003
2012
c. Long term trends in storrnwater nitrogen loads In urban
area ol Gwinnen County. GA, (or 3 control scenarios.
Figure 6. Comparison of population, land use, and pollutant loadings for Gwinnett
County, Georgia
-------
Table 7. Ranges in Pollutant Concentrations Found in
From Commercial and Residential Areas
Constituent
Total suspended solids (mg/L)
BOD (mg/L)
COD (mg/L
Total Phosphorus (mg/L)
Soluable Phosphorus (mg/L)
Total Kjeldahl nitrogen (mg/L)
Nitrate-nitrogen (mg/L
Total Copper (ug/L)
Total Lead (u,g/L)
Total Zinc (jlg/L)
Mean
10th Percentile
Urban Site
35
6.5
40
0.18
0.10
0.95
0.40
15
60
80
Concentration in
Median
Urban Site
125
12
80
0.41
0.15
2.00
0.90
40
165
210
Runoff3
Runoff
90th Percentile
Urban Site
390
20
175
0.93
0.25
4.45
2.20
120
465
540
" Source: Woodward-Clyde Consultants, 1990.
gen of about 154% and phospho-
rous of about 79% above the 1975
levels.
The importance of addressing
stormwater runoff in the early
stages of urban land development
is illustrated by the temporal in-
crease in nitrogen load from urban
areas under three control scenarios:
no control, control beginning in
1975, and control beginning in
1992 (Figure 6c). The nitrogen
loadings under the no control condi-
tion were derived based on urban
development trends in Gwinnett
county. The control conditions for
each of the treatment scenarios con-
sisted of a 50% reduction goal in ni-
trogen loading from all new devel-
opment and 10 to 25% reduction
goals from existing and retrofit
urban areas. The projection of an-
nual nitrogen loads to year 2012,
for controls beginning in 1975 and
controls beginning in 1992, shows
an overall annual reduction of 734
and 420 tons of nitrogen respec-
tively, corresponding to 45% and
25% of the projected value for the
uncontrolled condition. A compari-
son of the two control programs
shows that if implementation of
stormwater controls is delayed,
achieving lower levels of nitrogen
loadings may require im-
plementation of a retrofit pro-
gram with limited control options
consisting primarily of costly
structural practices.
As discussed earlier, the recent and
projected rapid growth rate of the
urban fringe area of Gwinnett
County is expected to parallel a
similar rapid growth rate of urban
fringe areas nationwide. A basic
principle of stormwater controls
for urban development is that it
is much more cost effective and
institutionally feasible to develop
controls for new development
than it is to retrofit old develop-
ment. At the time the 319 status
on water quality impairment was
last reported (1991), stormwater
runoff from urban and land devel-
opment activities representing only
about 2% of the Nation's land sur-
face was responsible for 18% to
62% of the reported impairment to
surface water bodies (see Table 3).
The growth rate of urban land areas for
the last 4 decades (based on Bureau of
Census data) has been about 20%
per decade creating the potential
for rapidly increasing impacts if
stormwater discharges from new
urban fringe growth is not ade-
quately managed.
Fully Developed Core Urban
Areas. In fully developed urban
areas, the amount of impervious
land is extensive, providing further
opportunity for pollutants to wash
off urban surfaces in even larger
amounts. Original stormwater sys-
tems were typically constructed for
flood control purposes. Water qual-
ity programs probably did not ad-
dress stormwater quality concerns
and runoff is typically directed to
surface water. Older, more estab-
lished urban areas are also charac-
terized by greater commercial and
industrial activities; the existence
of leaks, cross connections and
illicit discharges into sewer sys-
tems; and often the existence of
combined sewer systems. These
create opportunities for the release
of toxic pollutants and large
amounts of pathogens during wet
weather overflows of the combined
sewers.
Pollutant concentrations in
urban runoff vary considerably,
both during the course of a storm
event and from event to event at
a given site, from site to site
within a given urban area, and
from one urban area to another
across the country. This variabil-
ity is the result of variations in rain-
fall characteristics, differing water--
shed features that affect runoff
quantity and quality, and variability
in urban activities (Woodward-
Clyde, 1990). Table 7 presents
ranges of urban runoff pollutant
concentrations based on results of
-------
Table 8. Strength of Point and Nonpoint Urban Sources*
Wastewater type
Urban stormwater
Construction site
CSOs
Light industrial
Roof runoff
Untreated sewage
POTW effluent
BODs, rntfL
10 to 250
not available
60 to 200
8 to 12
3 to 8
160 (mean)
20 (mean)
SS, mg/L
3 to 11,000
10,000 to 40,000
100 to 1,100
45 to 375
12 to 216
235 (mean)
20 (mean)
Total N, mg/L
3 to 10
not available
3 to 24
0.2 to 1.1
0.5to4
35 (mean)
30 (mean)
Total P, mg/L
0.2 to 1.7
not availble
1 to 11
not available
not available
10 (mean)
10 (mean)
Lead, mg/L
0.03 to 3.1
not available
0.4 (mean)
0.02 to 1.1
0.005 to 0.03
not available
not available
Total coliforms,
MPN/100ml_
103to108
not available
105to107
10
102
107to109
104to106
"Source: Ellis (1986) as reported by Novotny (1992)
the Nationwide Urban Runoff Pro-
gram (NURP). Values represent
the mean of event mean concentra-
tion (EMC) pollutant values for the
median, 10th percentile, and 90th
percentile sites in the NURP data.
Although statistically significant
differences in EMGs were not de-
tected amount the three major
urban land use categories (i.e., resi-
dential, commercial, and mixed
urban), or among geographical loca-
tions or between runoff events (vol-
umes), nevertheless these data are
perhaps the best available for plan-
ning purposes in describing the gen-
eral quality of urban runoff. The
NURP data base does not, how-
ever, represent pollutant contribu-
tions from illicit connections,
spills, industrial activities, or dump-
ing, as these sources were not eval-
uated at the time NURP was con-
ducted.
A comparison of the pollutant
strength (i.e., concentrations) of
typical point and nonpoint urban
sources is presented in Table 8.
The pollution potential of urban
runoff carried by separate storm
sewers is similar to treated munic-
ipal wastewater, while that of
combined sewer overflows
(CSOs) is greater than treated
and less than untreated munici-
pal wastewater (Novotny, 1992).
Although the pollution strength
of CSOs is somewhat less than
that of raw wastewater, an over-
flow from a large storm may
shock the receiving waterbody
many times greater than a nor-
mal effluent load. Floatable de-
bris in CSOs and separate storm
sewers can further degrade receiv-
ing water. This debris represents
both an aesthetic problem and a
threat to aquatic life.
Impacts on Aquatic Ecosystems.
The aquatic ecosystems in urban
headwater streams (i.e., streams
whose upper reaches lie within
urbanizing areas) are particu-
larly susceptible to the impacts of
urbanization (Schueler, 1987).
The massive shift from natural
flow and channel conditions re-
duce the habitat value of the
stream. As reported by Schueler
(1987), studies of fish diversity and
abundance over time in urbanizing
streams [Dietemann (1975), Ragan
and Dietemann (1976), Klein
(1979) and MWCOG (1982)] have
shown that fish communities be-
come less diverse and are com-
posed of more tolerant species
after the surrounding watershed
is developed. Sensitive fish spe-
cies either disappear or occur
rarely. The total number of fish
in urbanizing streams also usu-
ally declines.
Similar trends have been noted
among aquatic insects which are a
major food resource for some spe-
cies offish (Schueler, 1987).
These species cling to rocks (or
other aquatic substrates) and rely
on the passing flow of leaf litter
and organic matter for sustenance.
Higher post-development sediment
and trace metals can interfere in
their efforts to gather food.
Changes in water temperature, oxy-
gen levels, and substrate composi-
tion can further reduce the species
diversity and abundance of the
aquatic insect community.
No single factor is responsible for
the progressive degradation of
urban stream ecosystems.
Rather, it is probably the cumula-
tive impacts of many individual
factors such as sedimentation,
scouring, increased flooding,
lower summer flows, higher
water temperatures, and in-
creased pollutants. A more de-
tailed discussion of the impacts of
urban stormwater pollution on re-
ceiving waters is presented in the
next chapter of this booklet.
-------
POLLUTANTS IN STORMWATER
AND EXAMPLES OF ASSOCIATED IMPACTS
The net effect of urbanization is to
increase pollutant export by several
orders of magnitude over pre-
development levels. The impact of
the higher export is felt not only on
adjacent streams, but also on down-
stream receiving waters such as
lakes, rivers, and estuaries. The na-
ture of the impacts associated with
specific urban stormwater pollu-
tants are reviewed in this chapter.
Examples of documented impacts
covering the range of pollutants
and source types are also presented.
The land activities that are likely to
result in the most severe receiving
water impacts are also identified
(after Schueler, 1987). The follow-
ing principal types of pollutants
found in urban runoff are addressed:
Sediment/habitat alteration;
Oxygen-demanding sub-
stances (organic matter);
Nutrients
- phosphorus
- nitrogen;
Toxic substances
- heavy metals
- oil and grease
- others;
Bacteria;
Floatables; and
the multiple impacts of several of
these pollutants acting in concert.
The locations of the fifteen case ex-
amples of documented receiving
water impacts caused by stormwa-
ter pollution are shown on the map
below. Examples which address
stormwater control practices are
also presented in the last chapter of
this booklet.
EXAMPLES OF STORMWATER DISCHARGE IMPACTS AND CONTROLS
J
Ketsey and Bear Creeks
Habitat Alteration/Sediments
Westport River
Multiple Impacts
Saddle River
Metals/Toxicants
Menomonee River
Urbanization
Duwamish River
Toxic Substances
Long Island Sound
Pathogens /DO
Milwaukee Harbor
Multiple Impacts
Passaic River
Multiple Impacts
Rouge River
Multiple Impacts
Anacostia River
Mutiple Impacts
San Francisco Bay
Metals
Dillon Reservoir
Eutrophication/Urban Growth
Occoquan Reservoir
Eutrophication
Lake Travis
Phosphorus
village Creek
Metals/Toxicants
-------
Sediment/Habitat Alteration
High concentrations of suspended
sediment in streams can cause mul-
tiple impacts including increased
turbidity, reduced light penetration,
reduced prey capture for sight feed-
ing predators, clogging of gills/fil-
ters of fish and aquatic inverte-
brates, reduced spawning and juve-
nile fish survival, and reduced ang-
ling success. Additional impacts re-
sult after sediment is deposited in
slower moving receiving waters,
such as smothering of the benthic
community, changes in the compo-
sition of the bottom substrate, more
rapid filling of small impound-
ments which create the need for
costly dredging, and reduction in
aesthetic values. Sediment having
a high organic or clay content is
also an efficient carrier of toxicants
and trace metals. Once deposited,
pollutants in these enriched sedi-
ments can be remobilized under
suitable environmental conditions
to pose an additional risk to benthic
and other aquatic life. A study of
Kelsey Creek in Seattle, WA, re-
vealed the impacts of stormwater
flows and sedimentation on fish
populations (Kelsey and Bear
Creeks).
The greatest sediment loads are ex-
ported during the construction
phase of any development activity.
Furthermore, in intensively devel-
oped watersheds, increased
streamflow can result in channel
degradation requiring streambank
erosion controls.
Oxygen Demanding Sub-
stances
Decomposition of organic matter
by microorganisms depletes dis-
Kelsey and Bear Creeks, Seattle, Washington
(Habitat Alteration/Sediments)
A comparison of urban Kelsey Creek to rural Bear Creek near
Bellevue, Washington (Pitt and Bissonette, 1984); indicated
significant interrelationships among the physical, biological,
and chemical characteristics. The urban creek, although not
grossly polluted, contained a limited and unhealthy salmon
fishery where many fish suffered from respiratory anomalies.
The most significant impact resulting from the urban area is
high flood flows which alter the stream channel, and carry pri-
ority pollutants, organics and metals through the stream sys-
tem. Low dissolved oxygen in the stream bed results in low
embryo survival rates.
Monitoring conducted by the City of Bellevue, the U.S. Geolo-
gical Survey, and the Municipality of Metropolitan Seattle re-
vealed that concentrations of metal and organic priority pollu-
tants are higher near the source areas than in the stream it-
self. Heavy metals were observed to originate primarily from
street dirt
Evaluations of control practices indicated that detention ba-
sins in a residential area did not significantly improve runoff
quality although peak flows were reduced by approximately
60%. A specialized street sweeper was needed to obtain effec-
tive removal of small dirt normally washed off by rain as regu-
lar street cleaning removed only a maximum of 10% of pollu-
tants. Bi-yearly catchbasin cleaning resulted in a maximum ef-
fectiveness of 25%.
Urbanization has led to rapid stormwater conveyance to
streams. However, these increased flows result in the trans-
port of metals and toxic pollutants through the stream system
with little deposition in the stream bed. If the flows are re-
duced, increased amounts of toxic materials are expected to
settle in the stream bed with increased negative effects on
aquatic life. However, reducing the flows would allow the
retainment of many smaller fish and organisms which are cur-
rently washed from the system. The monitoring and stormwa-
ter control management of Kelsey Creek demonstrates the im-
portance of balancing the benefits obtainable from reduced
flows with the potential impacts resulting from increased de-
position of toxic pollutants and organics.
solved oxygen (DO) levels in re-
ceiving waters, especially slower
moving streams and lakes and estu-'
aries. There are several measures
of the degree of potential DO deple-
tion, the most common of which
are the Biochemical Oxygen De-
mand (BOD) test and the Chemical
Oxygen Demand (COD) test Both
of these tests have problems associ-
ated with their use in urban runoff,
but it has been demonstrated (e.g.,
Rouge River, Western Long Island (
Soundsee insets) that urban run-
-------
off can severely depress DO levels
nfter large storms, and that BOD
solids can accumulate in bottom
sediment causing impacts during
periods of dry weather. BOD lev-
els can exceed 10 to 20 mg/1 during
storm events which can lead to an-
oxic conditions (zero oxygen) in
shallow, slow-moving or poorly-
flushed receiving waters. The prob-
lem is particularly acute in some
older urban areas, where storm run-
off BOD mixes with overflows
from combined or sanitary sewers.
The greatest export of BOD typi-
cally occurs from older highly im-
pervious, highly populated urban
areas with outdated combined
storm sewers. In contrast, only
moderate BOD export has been re-
ported from newer, low density sub-
urban residential development. A
study of the Rouge River, Michi-
gan, included an examination of
P3OD loadings from a highly devel-
oped basin, and is presented at
right (Rouge River).
Nutrients
The levels of phosphorus and nitro-
gen in urban runoff can lead to ac-
celerated eutrophication in down-
stream receiving waters. Gener-
ally, phosphorus is the controlling
nutrient in freshwater systems. The
greatest risk of eutrophication is in
urban lakes and impoundments
with long detention times (two
weeks or greater). Surface algal
scums, water discoloration, strong
odors, depressed oxygen levels (as
the bloom decomposes), release of
toxins, and reduced palatability to
aquatic consumers are among the
problems encountered. High nutri-
Knt levels can also promote the
Orowth of dense mats of green
Rouge River, Michigan
(Multiple Impacts)
The Rouge Basin, located in Southeast Michigan in the Detroit
metropolitan area, is a fan shaped basin with four river branches
draining 438 square miles. In addition to the four major river
branches, the Basin's surface water system includes numerous
tributary streams and over 400 lakes and ponds. The Basin con-
tains alt or part of 48 municipalities with a population of 1JS mif-
Iron people. More than 50 percent of the land in the Basin is de-
veloped for residential, commercial or industrial uses with por-
tions intensely urbanized (Newport and Davenport, 1988). The
City of Detroit and the older cities adjacent to Detroit have com-
bined sewers. Though the Rouge has been designated as a
warm water fishery and suitable for recreational and agricultural
use, applicable water quality standards, including dissolved oxy-
ten, are not being met. The Rouge has been designated as an
Area of Concern by the International Commission overseeing the
Great Lakes, as it contributes some of the greatest pollutant load-
ings to the Great Lakes. Annual stormwater loadings in 1985 to
the Rouge Basin were estimated to be 6,360,000 Ib/yr BODs (45%
of the total BODs load), 154,000,000 Ibs/yr TSS (88% of the total
TSS load), and 1,110,000 Ib/yr nitrogen (about twice the nitrogen
load from CSOs). CSOs contribute 5,489,000 Ibs/yr BODs (40%)
of the total load), 13,100,000 Ibs/yr suspended solids (8%) and
567,000 Ibs/yr nitrogen. Loadings are impairing the uses of the
Basin.
In July 1985, the Michigan Water Resources Commission passed
a resolution requesting the department of Natural Resources to
develop a Remedial Action Plan (RAP) addressing the water qual-
ity in the Rouge Basin. Of particular concern were the adverse
impacts from CSOs, illicit connections to storm drains and storm
water runoff. The RAP, published in 1989, recommends a 20 year
program of nearly $1 billion to eliminate CSOs, improve separate
sanitary sewers, upgrade treatment facilities and fund local
stormwater programs.
algae that attach to rocks and cob-
bles in shallow, unshaded headwa-
ter streams. High nutrient loads
from urban runoff, in combination
with other sources, can contribute
to eutrophication in both fresh and
tidal waters.
As a general rule of thumb, as im-
pervious area increases, nutrients
build-up on surfaces and runoff
transport capacities rise as well,
leading to high pollution loads. Ex-
ceptions include land under devel-
opment, and land activities that re-
ceive unusually high fertilizer in-
puts, such as golf courses, cemeter-
ies, and other intensively land-
scaped areas.
Examples of eutrophication caused
by nonpoint sources of nutrients in-
clude the Dillon Reservoir in Colo-
rado and the Occoquan Reservoir
-------
in Virginia. These are discussed in
the following chapter on control
practices.
Toxic Substances
Toxic substances are all defined as
materials capable of producing an
adverse response or effect in a bio-
;ogical system. A large number of
potentially toxic compounds are
routinely detected in urban
stormwater. These include trace
metals (lead, zinc, copper, and cad-
mium) pesticides and herbicides,
hydrocarbons (derived from oil and
grease, and gasoline runoff). These
toxic chemicals tend to accumulate
in benthic sediments of urban
streams, lakes, and estuaries. Both
the San Francisco Bay, and the
Duwamish River, Washington have
received significant loadings of
toxic substances and heavy metals
from stormwater runoff, and are
presented at right (San Francisco
Bay, Duwamish River).
Heavy Metals - Heavy metals are
of concern because of their toxic ef-
fects on aquatic life and their poten-
tial to contaminate drinking water
supplies. The heavy metals having
the highest concentrations in urban
runoff are copper, lead, and zinc
with cadmium a distant fourth.
However, when inappropriate con-
nections between sanitary and
storm sewers are present, other
heavy metals such as arsenic, beryl-
lium, chromium, mercury, nickel,
selenium, and thallium can be
found. A large fraction of the
heavy metals in urban runoff are ad-
sorbed to particulates and thus are
not readily available for biological
uptake and subsequent bioaccum-
ulation. Also, the typical periods of
exposure are those of urban runoff
San Francisco Bay
(Metals)
Southern San Francisco Bay is a highly urbanized estuary in the Santa
Clara watershed which encompasses the Silicon Valley (Mulmey,
1988). The Bay is a major navigable waterway for the U.S. Navy and
commerce, a valuable fishery for salmon and herring and a recreational
resource. Despite significant advances on controlling municipal and in-
dustrial point source pollution over the last two decades, water quality
impairment due to toxic pollution from urban runoff continues in the
southern bay segment The California Regional Water Quality Control
Board adopted water quality standards for copper, lead, nickel and zinc
to protect the beneficial uses of the Bay and, with local municipalities,
developed a water-quality/technology based program for reducing
urban runoff pollutants. Sources of pollution include urban runoff,
illicit connections, illegal dumping and construction/development sites.
Duwamish River, Washington
(Toxic Substances)
The Duwamish River is vital to Washington State's commerce as a pri-
mary navigational route, a major contributor to the State's salmon and
steelhead trout industry and a recreational resource (USEPA, 1990).
The lower six miles of the river flow through a heavily industrialized
area of Seattle including airplane factories, shipyards, metal scrap
yards, oil tank farms and port facilities. Though water quality im-
provements were observed through control of point sources, metals
and organic toxicants from industrial and urban nonpoint sources con-
tinued to degrade water quality in the river. In the early 1980's copper
concentrations in the river water exceeded the USEPA's acute freshwa-
ter criterion (18 ug/l), and lead concentrations exceeded the EPA
chronic freshwater criterion (3.2 ug/l)- The highest concentrations of
metals (lead, copper, zinc, mercury and cadmium) were found unevenly
distributed in the sediments of the river, suggesting that contaminants
came from localized sources (such as storm drains) where zinc concen-
trations were as high as 3,000 ppm and lead as high as 18,000 ppm.
Sediments inside a storm drain near a lead smelter were found to con-
tain 350,000 ppm (or 35%) lead. These sediments were removed and
handled as hazardous waste. Sources of pollutants along the river in-
cluded Illegal dumping In storm drains, mismanagement of Industrial
chemicals and wastes, industrial activities, and storm drain sediments.
Storm drain sediments contained significant concentrations of copper,
lead, arsenic, zinc, mercury, PCBs and cadmium from historic activities.
The Municipality of Metropolitan Seattle (Metro) received a Clean Water
Act Section 205 grant for sampling storm drain sediments to track pol-
lutants and locate sources. Eventually, the sediments themselves were
considered a significant source. Removal of sediments from storm
drain systems and reductions in contaminant inputs from industrial fa-
cilities eliminated major sources of contamination to the Duwamish
River. In 1989, sediments in a storm drain line near a lead smelter con-
tained 85 to 97 percent less lead than 1984 levels. Remedial actions at
smelter and electric transformer recycling facilities resulted in reduced
PCB, copper and lead concentrations in the stormwater. Reduced activ-
ity at shipyards (due to economic factors) and implementation of volun-
tary and mandatory BMPs in salvage yards reduced zinc loadings by 90
percent from 194 Ib/day to 15 Ib/day.
-------
events (typically under 8 hours),
which are much shorter than the ex-
posure periods used in bioassay
tests (typically 24 to 96 hours for
toxicity testing). Nonetheless, it is
likely that the heavy metals in
urban runoff are toxic to aquatic
life in certain situations, particu-
larly for the more soluble metals
such as copper and zinc. Addition-
ally, resuspension of bottom depos-
its from high flow events may im-
pact on downstream benthic inver-
tebrates. Compared to risks to
aquatic life, human health risks ap-
pear to be more remote.
Oil and Grease - Oil and grease
contain a wide variety of hydrocar-
bon compounds, some of which
(e.g., polynuclear aromatic hydro-
carbons) are known to be toxic to
aquatic life at low concentrations.
Hydrocarbons are often initially
as a rainbow colored film or
on the water's surface. Other
hydrocarbons, especially weathered
crankcase oil, appear in solution or
in emulsion and have no sheen.
However, hydrocarbons have a
strong affinity for sediment, and
much of the hydrocarbon load even-
tually adsorbs to particles and set-
tles out. Hydrocarbons tend to ac-
cumulate rapidly in the bottom sedi-
ments of lakes and estuaries, where
they may persist for long periods of
time and exert adverse impacts on
benthic organisms. The precise im-
pacts of hydrocarbons on the
aquatic environment are not well
understood. Bioassay data which
do exist are largely confined to lab-
oratory exposure tests for specific
hydrocarbon compounds. Remark-
ably few toxicity tests have been
performed to examine the effect of
urban runoff hydrocarbon loads on
Aquatic communities under the typi-
cal exposure conditions found in
urban streams.
Other Pollutants - Other toxic
compounds that have been detected
in urban runoff include pesticides,
herbicides, and synthetic organic
compounds. Concentrations of
these toxic substances in runoff
from residential and commercial
areas rarely exceed current water
quality criteria. However, it
should be noted that there has been
relatively little sampling of runoff
reported from industrial areas,
where toxic compounds might be
expected to be more prevalent (e.g.,
Duwamish River).
Examples of Impacts from Toxic
Substances. In-stream monitoring
of Village Creek in Birmingham,
Alabama (Water Quality Engineers,
1981not an inset) provides a clas-
sic example of stream degradation
due to intense urban development
At the stream's origin at Roebuck
Springs, the creek had excellent
physical and chemical characteris-
tics, supporting watercress and
other vegetation. By the time the
stream passed through the city, it
turned grey-green and had an oily
sheen and contained significant de-
bris. Further downstream at the
western limits of Birmingham, the
creek was dark green, had a putrid
odor and contained considerable oil
and grease. At this point the creek
was often anaerobic and contained
no fish or other biological life.
This study found that, on an annual
basis, more than 90 percent of the
copper loadings, more than 75 per-
cent of the chromium and zinc load-
ings, and about 40 percent of the
lead loadings originated from urban
runoff.
A study (Dong et al., 1979, and
Southeastern Wisconsin Planning
Commission, 1976not an inset)
of the Menomonee River near Mil-
waukee, Wisconsin indicated that
the upper, more rural reaches of the
river had an average of 40 times
more fish than the lower, urbanized
reach. The urban segments of the
river supported a significantly re-
duced and scattered fish population
and some segments were virtually
devoid of even highly pollution tol-
erant species. These conditions are
the combined result of higher con-
centrations of toxic pollutants and
poorer habitat conditions resulting
from increased flow velocities and
channelization. Further, the water-
shed benthic community is in poor
condition in the urban area. The
Menomonee study concluded that a
relatively small degree of urbaniza-
tion, less than 20 percent, was suffi-
cient to cause significant receiving
water degradation.
Studies at other locations have pro-
duced results similar to those cited
above. Interestingly, toxic pollu-
tants or long-term oxygen deple-
tion has been found to cause more
serious receiving water problems
than short-term, event-related oxy-
gen depletion or other concentra-
tion excursions. The long-term af-
fects due to accumulation of toxic
compounds in sediments and their
subsequent movement through the
food chain is especially pro-
nounced in urban receiving waters.
Studies on the Saddle River near
Lodi, New Jersey (Wilbur and
Hunter, 1980) found significant en-
richment of heavy metals (two to
seven times) in lower Saddle River
sediments (affected by urbaniza-
tion) as compared to upper rural
reaches (see also Saddle River case
-------
study at right) Similar results were
found in a stream near Champaign-
Urbana, Illinois (Rolfe and Rein-
hold, 1977not an inset), where
the upper two inches of sediment in
an urban stream reach had much
higher lead concentrations (almost
400 ug/g) than sediments in the
rural stream reaches. Species diver-
sity of plants and animals were
found to be lower in urban streams
as compared to streams in rural
areas. This impact is likely to be in-
fluenced by habitat and tempera-
ture changes, as well as pollutant
levels.
Bacteria
Bacterial levels in undiluted urban
runoff usually will exceed federal
public health standards for water
contact recreation and shellfish har-
vesting. Because bacteria multiply
faster during warm weather, it is
not uncommon to find a twenty-
fold difference in bacterial levels
between summer and winter. The
substantial seasonal differences
often found do not correspond with
comparable variations in urban ac-
tivities. This suggests that in addi-
tion to temperature effects, many
sources of coliform unrelated to
those traditionally associated with
human health risk (e.g., animal ex-
crement, illicit connections, leaking
sanitary collection systems), may
be significant Thus, despite the
high numbers of coliforms found in
urban runoff, in the absence of con-
tamination from sanitary sewage,
the health implications are unclear.
The current literature suggests that
fecal coliform may not be consis-
tently reliable in identifying human
health risks from urban runoff pol-
lution (Moffa, 1990). The impact
of bacterial pollution in coastal wa-
Saddle River, New Jersey
(Metals/Toxicants)
Saddle River drains an area of 59 mi2 extending from the headwa-
ters in Southern Rockland County, NY to Garfield, NJ where it in-
tercepts the Passaic Riven The study was centered around the
lower reaches of the Saddle River and encompasses the borough
of Lodi, NJ. The area is heavily urbanized with 60% of the area as
single-family housing, 6% multi-family residential, 11 % indus-
trial, 12% commercial, 10 % open and 2 % public and municipal
(Wilber and Hunter, 1980), Because municipal and industrial
wastewater is dispatched to Passaic Valley Sewerage Authority
via trunk sewers, the only pollution from Lodi is from nonpoint
sources. Eleven individual storm hydrographs were monitored
at the storm sewer outfalls during the project period. Samples
were collected manually at 5 to 10 minute intervals over the com-
plete hydrograprt. Water samples were analyzed for lead, zinc,
copper, nickel, and chromium. The major contributors of heavy
metals in stormwater were lead and zinc. They accounted for
89% of the total metals observed. Copper, nickel and chromium
were usually found in smaller quantities.
Rainfall as a source of metals to the Saddle River was investi-
gated by collection of rainwater samples by local residents,
The concentration in precipitation was between 4 and 10 percent
of the concentration in runoff. Peak concentrations of heavy met-
als in runoff were observed within the first half hour after the initi-
ation of runoff, thus giving a first flush effect. In general, metal
loadings were correlated with increased percentages of commer-
cial and industrial land-use. An average of 66 percent of the total
solids for the three storms studied were removed after four
hours of settling. The majority of the lead and zinc were found in
the non-settleable solids fractions. Copper was found primarily
in the soluble plus colloidal fractions.
ters is illustrated in the Western
Long Island Sound and Westport
River, Massachusetts case studies
(see insets next page).
Studies conducted by the National
Oceanic and Atmospheric Adminis-
tration (NOAA, 1988,1989, and
1990) indicate that urban runoff is
a major pollutant source which ad-
versely affects shellfish growing
waters. The NOAA studies identi-
fied urban runoff as affecting over
578,000 acres of shellfish growing
waters on the East Coast (39 per-
cent of harvest-limited area);
2,000,000 acres of shellfish grow-
ing waters in the Gulf of Mexico
(59% of the harvest-limited area);
and 130,000 acres of shellfish
growing waters on the West Coast
(52% of harvest-limited areas).
Although nearly every urban and
suburban land use can export bacte-
ria at levels which will violate
health standards, older and more in-
tensively developed urban areas
typically produce the greatest ex-
port The problem is especially sig-
nificant in urban areas that experi-
ence combined or sanitary sewer
overflows that export bacteria de-
rived from human wastes.
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Floatables
Floatable debris in stormwater run-
off commonly includes plastic and
paper products, garden refuse, tires,
and metal and glass containers.
These pollutants degrade the aes-
thetic quality of both receiving wa-
ters and river banks and shorelines.
Vegetation and wildlife may also
be impacted. In the tidal Anacostia
River, Maryland, floating debris
has impaired restoration efforts by
hindering the establishment of
emergent vegetation (USACOE,
1990). Fish and aquatic wildlife
mortality may also be attributed to
debris, due to either ingestion or en-
tanglement in the slowly decompos-
ing materials.
Western Long Island Sound
(Pathogens/DO)
Long Island Sound is a major marine resource for the state of
Connecticut as well as a source of recreation to more than ten
million New Yorkers. Water quality of Western Long Island
Sound has been degraded by both point and nonpoint dis-
charges which have resulted In low DO concentrations, toxic con-
tamination, and closure of beaches and commercial shellfish
beds due to high fecal coliform concentrations. Combined sewer
overflows and urban stormwater runoff are two significant pollu-
tion sources to Long Island Sound. It is estimated that up to 85%
of the sewer lines in New York City are combined. Urban runoff
is the largest identified nonpoint pollution source, based on the
number of estuaries along the Connecticut shoreline impacted.
Stormwater runoff pollution from New York City has been Im-
plicated in a New York Harbor Water Quality Survey because of
the increase in coliforms and reduction in DO observed after rain-
storms. Increases In coliform levels between 3 and B times were
observed after rainfall events for Jamaica Bay, Upper Harlem
River, Gowanns Canal, Hudson River, Lower East River, and
Western Long Island Sound. These increases were due to urban
stormwater runoff and CSOs (City of New York, 1987).
Analysis of pollution sources to
Buzzards Bay is typified by loads
to the Westport River and includes
pollution from surface runoff, boat
discharges, storm sewers, septic
systems, feedlot and pasture run-
off. Nonpoint source pollution has
been implicated based on the high
concentrations of coliform bacteria
observed after rainfall events. Bac-
teria, nutrients, and solids contami-
nation from nonpoint sources has
impacted water quality of the East
Branch of the Westport River
(EBWR), one of the most produc-
tive shellfisheries on the south
shore of Massachusetts. Violations
of Class SA (for tidal, salt water
suitable for primary contact recre-
ation) water quality criteria for coli-
form bacteria have forced the clo-
sure of 960 acres of shellfish beds
(over 75% of the shellfish produc-
ing area) in 1979, including soft-
shell clams, quahog and oyster
beds. Since between 1983 and
1985,555 acres of the 960 acres per-
Westport River, Massachusetts
(Multiple Impacts)
manently closed In 1979 have been
reclassified to allow periodic har-
vesting. The area between Gun-
ning Island and Cadman's Neck
was closed for a minimum of eight
days following a rainfall of one inch
or more. These standards were not
sufficient for the area north of
Cadman's Neck (200 areas), which
In 1985 showed bacterial levels in
excess of the standard for at least
10 to 16 days after rainfall; this area
remains permanently closed. It has
been estimated that annual losses
in commercial shellfishlng exceed
1$ million not including losses to re-
creational diggers.
Westport is primarily a rural com-
munity that has experienced a pop-
ulation growth of 25% between
1970 and 1975. Most of the land in
the drainage basin is undeveloped,
consisting predominantly of for-
ested land with smaller areas of
wetlands and lakes. Agricultural
land, primarily cropland with some
pastureland, is the second largest
land use within the region. Resi-
dential, commercial and industrial
land comprise less than 10 percent
of the total watershed. In the past
35 years, significant land use
changes have occurred within the
southeastern Massachusetts area.
From 1951 to 1971, developed land
within Westport increased by 96%,
while open, forested, and agricul-
tural land decreased by 19%, The
conversion of undeveloped land
continued with residential land use
increasing by 1,500 acres and com-
mercial land increasing by 110
acres between 1971 and 1981.
Land use data developed by the
Soil Conservation Service and the
Environmental Protection Agency
showed that between 1983 and
1988 combined residential and
urban land use increased by 13%.
Agricultural, forested, and open
land use decreased by 8% during
this same period (Metcalf & Eddy,
1989).
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EXAMPLES OF SUCCESSFUL
STORMWATER CONTROLS
In this last chapter we examine gen-
eral stormwater control practices
and present examples of successful
stormwater programs implemented
at various stages of urban develop-
ment. A basic principle of
stormwater controls for urban de-
velopment is that it is much more
cost effective and institutionally
feasible to develop controls for
new development than it is to ret-
rofit old development. Structural
practices for stormwater pollution
control require not only capital but
operation and maintenance costs,
and are often constrained by spatial
and financial limitations in core
urban areas. In addition, some
structural controls can destroy the
resource it is designed to protect
due to disruption of the hydrologic
Examples of
Non-structural Stormwater
Practices
Q Zoning Ordinances
Q Subdivision Regulations
Q Capital Improvement Plans
Q Site Plan Reviews
Q Planned Unit Development
Reviews
Q Restrictive Covenants
Q Environmental Impact As-
sessment/Statements
Q Public Education Programs
Q Growth Management
Q Buffers and Setbacks
Q Environmental Permitting
Q Pollution Prevention for All
Sources
Q Spill Control Programs
Q Road Maintenance Pro-
grams
cycle. In contrast, non-structural
practices may be included in the de-
velopment process, for which mu-
nicipalities usually have pre-exist-
ing permitting programs. Combin-
ing both types of controls into an
integrated stormwater management
program can result in effective
water quality protection at minimal
cost. Before presenting representa-
tive case studies, the practices for
control of stormwater are first de-
fined.
Control Practices
Non-Structural Practices. Non-
structural practices are those not re-
quiring construction or mainte-
nance. These differ from structural
practices in that they are preventa-
tive in nature, and have the poten-
tial to be more cost effective espe-
cially if implemented early in the
site planning stages. They include
such practices as: regional com-
prehensive stormwater manage-
ment programs; planning future de-
velopment to minimize stormwater
runoff; limiting the amount of im-
pervious surface in new and retrofit-
ted development; instituting fertil-
izer and pesticide management pro-
grams; requiring setbacks from sur-
face water and wetlands to protect
their environmental integrity; siting
infrastructure so as not to encour-
age development in environmen-
tally sensitive areas that are critical
to maintaining water quality; requir-
ing the use of best management
practices through land development
regulations and site plan approval;
and inspecting stormwater manage-
ment systems and erosion control
structures to ensure they are func-
tioning properly.
Examples of Structural
Stormwater Practices
Developing Areas
Q Extended Detention Ponds
Q Stormwater Wetlands
Q Multiple Pond Systems
Q Infiltration Trenches
Q Infiltration Basins
Q Filter Strips
Core Urban Areas
Q Illicit Connection Controls
Q Porous Pavements
Q Stormwater Detention/Wet-
land Retrofits
Q Sand Filters
Non-structural practices for control-
ling stormwater pollution have typi-
cally centered around preventing
land use disruptions on areas criti-
cal to maintaining water quality
and reducing the source of pollu-
tion.
Structural Practices. Structural
management practices are defined
as those designed and constructed
to mitigate the adverse impact of
stormwater runoff. The selection
and use of individual practices has
typically been based on land use ac-
tivities, existing structures, hydro-
logy and climate, soil type and
other site specific conditions.
-------
In addition to installation costs,
structural practices usually require
continuing operation and mainte-
nance efforts. Table 9 summarizes
the site-specific and maintenance
burdens of several selected struc-
tural practices.
The lack of adequate maintenance
and upkeep may dramatically re-
duce their effectiveness in remov-
ing pollutants from stormwater run-
off. For example, a sand filter sys-
tem in Maryland that had not been
maintained for several years ap-
peared to be clogged with sediment
and grease to the point that the op-
eration of the system may have
been impaired (Shaver, 1991).
Separate storm sewers may also re-
ceive materials other than stormwa-
ter (e.g., illicit connections from in-
dustrial and commercial facilities).
Controlling these sources may in-
'volve structural practices such as
conventional wastewater treatment
units, or repairing/retrofitting con-
nections to the storm sewer system.
Integrated Management Pro-
grams. The stormwater manage-
ment practices presented above
may be used in conjunction with
one another, taking an integrated
approach to minimizing stormwater
impacts. Structural practices could
be targeted at areas already built
up, while developing areas utilize a
more non-structural approach.
Strategies have been shown to be
successful when targeted to land
disturbance, not necessarily land
use, and should reflect land use/ac-
tivity changes. Guiding develop-
ment to areas capable of sustaining
growth without excessive impacts
to the natural, environment, and en-
couraging the implementation of
stormwater practices as develop-
ment proceeds, can minimize the
need for future stormwater control
efforts. Many local governments
have adopted integrated stormwater
management programs to regulate
development activities within their
jurisdictions. Several states, includ-
ing Oregon, New Jersey, Delaware,
and Florida, have adopted com-
prehensive plans involving guid-
ance of future growth and avoid-
ance of water quality and quantity
impacts associated with uncon-
trolled development.
Land Disburbance/Activity
The extent of stormwater pollution
problems is dependent upon the
land disturbance/activity which in
turn is a function of the stage of the
urbanization process. The range of
stormwater management options ap-
plied has been based to a certain ex-
tent on the stage of land develop-
ment, each stage representing a
unique set of challenges and oppor-
tunities. Three land development
stages that have been addressed by
states and municipalities while de-
veloping stormwater management
programs are defined below.
Within each of these stages a brief
description of relevant case studies
illustrating different stormwater
control approaches is presented.
Undeveloped Areas. Undeveloped
areas consist of relatively unurbanized
land with low population densities. Al-
though the land use is primarily rural,
the proximity and location of these
lands presents the potential for even-
tual development into urban and sub-
urban settings. Stormwater runoff
from these areas currently results pri-
marily from agricultural, forestry,
and resource extraction activities.
Table ft. Regional, Site Specific, and Maintenance Considerations for ,
Structural Practices to Control Sediments in Stormwater Runoff
BMP
Option
Infiltration
basins
Vegetated
filter strips
Filtration
basins and
sand filters
Extended
detention
ponds
Wet ponds
Constructed
stormwater
wetlands
Size of
Drainage
Area
moderate to
large
small
widely
applicable
moderate to
large
moderate to
large
moderate to
large
Site
Requirement
deep
permeable soils
low density
areas with low
slopes
widely
applicable
deep soils
deep soils
poorly drained
soils, space
may be limiting
Regional
Restrictions
arid and cold
regions
arid and cold
regions
arid and cold
regions
few restrictions
arid regions
arid regions
Main-
tenance
Burdens
high
low
moderate
dry ponds
have
relatively
high
burdens
low
annual
harvesting
of
vegetation
Longevity
low
low if poorly
maintained
low to
moderate
high
high
high
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In undeveloped areas stormwater
management programs may be inte-
grated with local planning and regu-
latory programs at an early stage of
development These management
programs, relying primarily on non-
structural practices, have been
aimed at minimizing future degra-
dation of water quality.
Depending on the expected degree
and rate of development, integrated
management programs have been
tailored to address pollution gener-
ating activities associated with the
various phases of urbanization.
Many local governments, aware of
the consequences of uncontrolled
urbanization, have adopted plan-
ning programs in which stormwater
pollution considerations were
major decision criteria. Two case
studies in which stormwater pollu-
tion control practices were ad-
dressed at an early phase of devel-
opment are presented. These case
studies are the Occoquan Reser-
voir, Virginia (see inset) which uti-
lized zoning ordinances to achieve
stormwater management goals, and
Lake Travis, Texas in which point
and nonpoint pollution concerns
were integrated into a single man-
agement program, discussed below.
Lake Travis, Texas
Phosphorus
The Highland Lakes, a chain of res-
ervoirs in Central Texas, provide
hydroelectric power, flood control,
and recreational opportunities. Sedi-
Occoquan Reservoir, Virginia
(Eutrophication)
The Occoquan Reservoir Is the major water supply for 600,000 people In the
Virginia suburbs of Washington, DC. The 9.8 billion gallon reservoir is lo-
cated at the mouth of a 580 square mile watershed in Northern Virginia. Be-
tween 1976 and 1978 a special planning study carried out by the Northern
Virginia Planning District Commission concluded that nonpoint sources of
pollution were a significant contributor to water quality problems In the Oc-
coquan Reservoir, and were much higher than originally thought (NVPDC,
1987, NVPDC, 1990). The primary concern for the reservoir was eutrophtea*
tlon resulting from nitrogen and phosphorus loadings.
In response to this study, the Occoquan Basin Nonpoint Pollution Manage-
ment Program was Initiated in February, 1982 to address nonpoint source
pollution (NPS) In the Occoquan watershed.
This program Is designed to manage nonpoint source pollution loadings
from each of the watershed's Jurisdictions, with each developing Its own
NPS program. Most of these local programs utilize Best Management Prac-
tices compiled In a BMP Handbook for the Occoquan Watershed. BMPs In-
cluded in the Handbook include extended detention ponds, dry ponds, Inf It-
tratton trenches and non-structural practices such as fertilizer application
controls, street sweeping, and zoning changes.
The Program maintains a water quality model of the watershed to analyze
the effects of land use changes on water quality. In 1982 Fairfax County
"downzoned" approximately 27,000 acres In the Occoquan watershed to re-
duce the future nonpoint source pollution loads entering the reservoir,
based on results from the model. Downzoning, the process of reclassifying
existing zoning regulations (In this case to lower density residential), Is
used to reduce development Impacts. The validity of basing land use deci-
sions designed to protect water quality on modelling results was recently
upheld in Fairfax County Circuit Court.
mentation, eutrophication, and
toxic contamination problems
caused by stormwater runoff to
these lakes prompted the Lower
Colorado River Association
(LCRA) to develop the Water Qual-
ity Leadership Policy (WQLP) in
1988 (Hartigan and Wilwerding,
1991). Analysis of the monitoring
data of the Highland Lakes showed
that over 90% of the pollution was
from nonpoint sources. LCRA esti-
mates that the NPS loads to the
Lake Travis basin could increase
by 200 to 600 percent in the future,
largely due to the conversion of
rangeland into urban and suburban
development The WQLP initiated
public education efforts along with
a regulatory program to control
nonpoint source pollution in its ten
county district. The Lake Travis
Nonpoint Source Pollution Control
Ordinance was adopted by the
LCRA Board of Directors in De-
cember 1989 and went into effect
on February 1, 1990. The ordi-
nance targets new urban and subur-
ban development in the 250 square
mile area of western Travis County.
The Lake Travis Ordinance estab-
lishes-a set of performance stan-
dards that require new develop-
ments to remove a specified
amount of the annual NPS pollu-
tion load, depending on the site's
proximity to the shoreline and the
slope of the property. Sites within
500 feet of the lake and/or those on
steep slopes require a higher level
of runoff treatment than those in-
land or on flatter ground. In gen-
eral, the more intensively a site is
developed, the more pollution must
be removed. This approach recog-
nizes the link between land use and
NPS pollution; however, there are
-------
no land use control stipulations in
the ordinance.
The Ordinance requires all land
owners proposing to develop land
within the Lake Travis watershed
to submit an application for review
and plans on how the surface run-
off from the site will be treated.
The plan must include temporary
erosion and sediment control plans
including a restoration program for
all disturbed areas, description of
the design and location of struc-
tural practices used to meet the per-
formance standards, and establish-
ment of a maintenance organization
to ensure that the structural prac-
tices are adequately maintained.
An ongoing program conducted
jointly by LCRA, the US EPA Re-
gion 6 and the U.S. Geological Sur-
vey will evaluate the Ordinance on
a periodic basis to determine
whether the standards are adequate
to protect the water quality of Lake
Travis and whether or not the struc-
tural best management practices are
adequate to meet the standards of
onsite pollutant removal.
Developing Urban Areas. Devel-
oping urban areas are those lands
currently experiencing new devel-
opment or redevelopment resulting
in significant changes to the land-
scape. These areas include subur-
ban cities and urban fringes located
adjacent to urban areas.
Many of these areas are experienc-
ing a dramatic rise in population
compared to well established urban
areas. For instance, between the
1970 and the 1980 period, the popu-
lation of urbanized areas increased
30 times more (an increase of 18.9
million) than core cities with a pop-
Klation exceeding 100,000. One ac-
vity affecting storm water quality
in developing areas is land distur-
bance in and around construction
sites where exposed soils results in
increased sedimentation, erosion,
and nutrient transport. Land distur-
bance in these areas may result in
severe stormwater pollution if ade-
quate control programs are not in-
corporated into the development
process. Yet these areas, where the
majority of new growth and land
disturbance and conversion are oc-
curring, are not necessarily covered
under the Phase INPDES stormwa-
ter program. Moreover, an import-
ant characteristic of these areas re-
sulting from land conversion con-
sists of permanent changes to land
use patterns. These changes induce
a significant disruption to the hy-
drologic cycle and modification of
runoff water quality (modification
of natural vegetation and infiltra-
tion rates, increase storm peak dis- .
charges and transport capacities,
and decrease of low flow especially
during prolonged dry periods).
Stormwater management efforts
have been directed primarily to-
ward controlling construction site
stormwater runoff. Stormwater pol-
lution control efforts have been
minimized by retaining and treating
stormwater onsite rather than by ad-
dressing impacts occurring offsite.
To address impacts originating
from developing areas, several
state and local agencies have devel-
oped comprehensive programs in-
corporating both structural and non-
structural practices. Typical com-
prehensive studies include the An-
acostia River study (see inset next
page) that involves a sediment con-
trol program designed to control
stormwater pollution from construc-
tion sites, and the Dillon Reservoir
study in Colorado, discussed
below, which addresses both
stormwater and point source dis-
charges.
Dillon Reservoir, Colorado
Eutrophication/Urban Growth
Dillon Reservoir is a large (2970
acre) impoundment of the Blue
River in Colorado. The Reservoir
supplies drinking water to the Den-
ver metropolitan area and is used
for recreation, fish habitat and agri-
culture. Water quality degradation,
primarily eutrophication and sedi-
mentation, has occurred since the
Reservoir's construction over 20
years ago. At higher elevations the
watershed is primarily undevel-
oped, while the lower elevations
contain three major municipalities,
four major treatment plants, hous-
ing developments and a large mo-
lybdenum mine. A study com-
pleted in 1983, supported by the
EPA through the Clean Lakes Pro-
gram of the Clean Water Act, identi-
fied phosphorus as the primary con-
tributor to the Reservoir's eutrophi-
cation. According to the Clean
Lakes study, which evaluated 1982
Reservoir phosphorus levels,
human activities were found to ac-
count for about 1/2 of the total
phosphorus load, and of this, be-
tween 1/2 and 2/3 was attributed to
urban nonpoint sources including
runoff from parking lots, golf
courses, and construction sites, as
well as leakage from septic tanks.
The Northwest Colorado Council of
Governments, cooperating with
local and state agencies, developed a
strategy for phosphorus control by
holding the phosphorus loadings to
existing (1982) waste load alloca-
tion levels (4609 kg/yr) and allow-
ing no further water quality degrada-
tion (USEPA, 199 Ib). To meet the
-------
phosphorus loading while allowing
for future growth in the basin, non-
point source controls were encour-
aged by allowing point/nonpoint
source trading at a ratio of 2:1. For
every 2 kg of nonpoint source phos-
phorus removed, 1 kg of phospho-
rus credit is added to the point
source limit. This system provided
for maintenance of existing phos-
phorus levels in the Reservoir,
while accounting for increased
loading from growth. In addition
to providing environmental bene-
fits, this program provides eco-
nomic benefits and incentives for
nonpoint source reduction. The 2:1
ratio provides a margin of safety in
the source trading program, and if
further phosphorus reduction in the
Reservoir is desired, the ratio can
be adjusted.
To date, only one point/nonpoint
source trade has been completed.
The low volume of trade has
caused the program to operate dif-
ferently than was first envisioned.
The low volume of trade occurred
because the POTWs were able to
achieve some of the highest phos-
phorus removal efficiencies in the
nation using expensive advanced
treatment technology. Conse-
quently, point/nonpoint source trad-
ing has played only a minor role in
the overall basinwide phosphorus
mitigation strategy. The major con-
straint to future development is a
limit on nonpoint source phospho-
rus loading.
Although total phosphorus loading
was only 5,559 pounds in 1989,
i.e., 54 percent of the total phospho-
rus allowed, additional reductions
in phosphorus loadings must result
from reductions in nonpoint
sources. Nonpoint/nonpoint trades
Anacostla River Case Study, Metropolitan Washington, DC
(Mutiple Impacts)
The Anacostia River watershed covers approximately 170 square miles
of the metropolitan Washington, DC area. Roughly 145 square miles of
the basin are in Maryland with the remaining 25 square miles within the
District of Columbia. Nonpoint source pollution associated with storm
runoff from construction sites were analyzed based on data collected
from 9 subbasins In a 32 square mile area north of Washington, DC in
Montgomery County, MD (Yorke and Herb, 1978).
From 1963 to 1974 the study area experienced extensive urbanization, a
process that continued beyond the period of the study. Urban land use
Increased from 3 to 11% from 1966 to 1974 and suburban land increased
from 6 to 23% of the total drainage area, resulting in significant in*
creases in impervious areas. Impacts resulting from urbanization dur-
ing this time Included the loss of aquatic habitat and consequent de-
cline In the biological community, increased sediment transport and
bank erosion, widening of the stream channel, and Increased flooding.
Fish species in the Anacostia River declined from an average of 7.2 spe-
cies per station in 1948 to 3.6 species per station in 1972. The decline
of fish species was attributed to loss of habitat and increased stream
sedimentation.
Changes in stream sediment yield were correlated to land development
which averaged 3% of the basin during the study period. Regression
analysis of this relationship Indicated that 40% of the changes In sedi-
ment yield were due to construction activities. From this analysis sedi-
ment yield from construction sites was estimated to range from 7 to 100
tons per acre per year, with an average of 32.7.
In 1971 an existing sedimentation control program from construction/de-
veloping areas was enforced, requiring developers to incorporate and
maintain control practices at their construction sites. The most com-
monly used measures were: 1} mulch and/or temporary vegetation to
protect exposed slopes; 2) Interceptor dikes to reduce erosion on rights
of way by temporarily diverting storm runoff to where the water can be
transported with minimal erosion; 3} grassed waterways, level spread*
ers, and grade stabilization structures to convey storm runoff through
the construction site without erosion, 4) diversion berms to'divert storm
runoff from areas with critical slopes, 5) sediment basins to trap and
store sediment from construction sites before It can enter the stream
system. The program also included a number of non-structural prac-
tices, such as keeping the smallest practical area of land exposed for
the shortest period of time, and fitting the development plan to the to-
pography and soils so as to create the least erosion possible.
This program resulted In the implementation of control practices in up
to 60% of construction sites in four subbasins. The enforcement of
these practices resulted In an estimated reduction In suspended sedi-
ments from construction sites of 60 to 80%. .It was estimated that the
suspended sediment load in the Anacostia River basin between 1962
and 1974 would have been reduced by 50% if strictly enforced sediment
control had been used throughout the period. At the time of the study,
the cost of sediment control practices on 1,900 acres was estimated to
be $1,030/acre corresponding to $19 for each ton of sediment control
This study indicated that costs could be reduced If construction were
limited to areas with slopes less than 10% and sites immediately adja-
cent to stream channels were avoided. Those non-structural control
practices would have the effect of preventing the problem before It oc-
curred.
-------
are beginning to be used to offset
nonpoint sources from new devel-
opment through the control of exist-
ing nonpoint sources. For exam-
ple, the Frisco Sanitation District
built a series of concrete vaults
(man holes) to control runoff. Fil-
tering the runoff through perforated
pipes resulted in removal efficien-
cies of 50 to 70 percent for total
phosphorus and the alleviation of
drainage problems. Encouraged by
the results of the first project, the
district expanded its program to an-
other section of town with the help
of federal funds administered
through the Clean Water Act's non-
point source management program.
Since the Frisco Sanitation District
did not need all the phosphorus
credits it earned, the credits were
set aside for the construction of a
new town golf course. The result
was a nonpoint/nonpoint source
ade. The removal capabilities of
is project will be monitored to de-
termine the actual phosphorus cred-
its applied to the new golf course.
The county-owned Snake River
treatment plant is also involved in a
nonpoint source control trading
project. The project will offset in-
creased contributions of phospho-
rus to Dillon Reservoir resulting
from a stream diversion plan by re-
ducing loads from another stream
that is currently responsible for the
highest phosphorus load entering
the Reservoir. The diverted stream
is expected to load an additional
200 pounds of phosphorus into the
Reservoir. The phosphorus reduc-
tion will occur on Soda Creek
where the treatment plant has con-
structed a discharge control struc-
ture using an existing road cause-
way over the Reservoir to intercept
id filter the stream flow. When
Reservoir levels are low, phospho-
rus removal efficiencies of 50%, or
75 pounds, are expected. After
modelling studies assess the actual
removal achieved by the dam, phos-
phorus discharge credits will be
shared equally by the Snake River
Plant and the Denver Water Board.
The Dillon experience illustrates
the importance of a comprehensive
basin-wide management approach
which does not focus on isolated
point sources. Modelling studies
considered the contributions from
point, nonpoint, and background
sources of phosphorus to determine
the maximum loadings from these
categories that would maintain the
in-lake phosphorus standard of
0.0074 mg/L. As a result of
Dillon's protective planning, 1989
phosphorus loads to the Reservoir
totaled only 53 percent of the criti-
cal load. Modelling is an essential
component of this water quality-
based approach to evaluate current
control strategies and predict the
impact of future development
Core Urban Areas. Existing
urban areas, with typical popula-
tion densities greater than 100,000,
are communities with limited poten-
tial for new development. These
existing, incorporated urban areas
with typical populations greater
than 100,000 are currently subject
to Phase INPDES stormwater per-
mit requirements. The Phase I
NPDES stormwater program also
applies to some highly populated
counties.
Original stormwater systems in es-
tablished urban areas were typi-
cally constructed for flood control
purposes. Water quality programs
probably did not address stormwa-
ter quality concerns and runoff is
typically directed to surface water.
These urban areas are characterized
by high percentages of impervious
surfaces, which contribute to in-
creased storm water discharges and
pollutant transport capacities. Re-
duction of infiltration rates and
groundwater recharge also results
in lower baseflows and higher pol-
lutant concentrations in receiving
waters, especially during prolonged
dry periods. Other stormwater im-
pacts include increases in tempera-
ture and concentrations of toxic
chemicals, nutrients, heavy metals,
oil, grease, and pesticides.
Core urban areas may also experi-
ence stormwater pollution prob-
lems resulting from illicit connec-
tions, leaking sanitary sewage sys-
tems, or ground water infiltration.
Illicit connections can often be
traced to the initial development of
the storm sewer system, or arise
during redevelopment where storm
sewers are either mistaken for sani-
tary sewers or intentionally used
for wastewater conveyance. In in-
dustrial facilities, floor drains or
other discharge points which are
connected to the separate storm
sewer system may receive spills,
rinse waters, or process waste-
waters that should be sent to a treat-
ment plant. Illicit connection pro-
grams are directed at identifying
such problems for corrective action.
Stormwater control practices in es-
tablished urban areas have typically
included retrofits of detention ponds
and controls on combined sewer sys-
tems as well as the construction of
wetlands and sand filters. As devel-
opment proceeds, the range of avail-
able non-structural options de-
creases. The following representa-
-------
live case studies highlight a num-
ber of stormwater control pro-
grams. The Kelsey/Bear Creeks,
Washington, case study below ex-
amines stormwater impacts from
developed areas, and the effects of
street sweeping, catchbasin clean-
ing, and detention ponds on runoff
quality and quantity. Various
stormwater control practices in the
Milwaukee metropolitan area were
evaluated using a computer simula-
tion model (see inset next page).
The Anacostia Watershed Retrofit
Project (see inset below) illustrates
a basin-wide approach to storm
sewer retrofitting. Additional ex-
amples from core urban areas are
also included.
Kelsey/Bear Creeks, Washington
Habitat Alteration/Sediments
Kelsey Creek (see page 22 inset) is
located in a highly urbanized sub-
urb of Seattle, Washington. The
watershed is 90% developed with
residential units and commer-
cial/light industry uses (Pitt and
Bissonnettee, 1984). Kelsey
Creek, a natural water channel, was
developed to convey stormwater
from the City of Bellevue to Lake
Washington, a major water body in
the Puget Sound area. The creek
serves as a recreational resource
and has a productive, but limited,
salmon fishery. Increased peak
flows from urban development dra-
matically altered the stream chan-
nel causing severe streambed ero-
sion. The number and diversity of
aquatic organisms declined as bed
scouring and the resultant deposi-
tion of suspended sediment de-
stroyed stream habitat. Reduced
dissolved oxygen in the sediments
depressed salmon embryo survival.
The fish population adapted to the
degrading environment by shifting
species composition from coho
salmon to less sensitive cutthroat
trout.
Urban stormwater was monitored
for six metals and suspended sol-
Anacostia Watershed Retrofit Project,
Metropolitan Washington, DC
(Multiple Impacts)
Opportunities for urban retrofitting are limited in developed water-
sheds, but they can be implemented after extensive onsite evalua-
tions. In the 179 square mile Anacostia watershed In Montgomery
County, MD, over 125 sites were Identified as candidates for retrofit-
ting between 1989 and 1991 (Schueleret al., 1991). Retrofit operations
included source reduction, extended detention (ED) marsh ponds or
ED ponds to handle the first flush, additional storage capacity in the
open channel, routing of stormwater runoff away from sensitive chan-
nels, diversion of the first flush to sand-peat filters, and installation of
oil/grit separators in the drain network itself. The most commonly
used technique In the Anacostia watershed is the retrofit of existing
dry stormwater detention or flood control structures to improve their
runoff storage and treatment capacity. Existing detention ponds are
maintained by excavation, adding to the elevation of the embankment,
or by construction of tow-flow orifices. The newly created storage is
used to provide a permanent pool, extended detention storage, or
shallow wetland. Nearly 20 such retrofits are in some stage of design
or construction in the Anacostia watershed.
ids. Dry weight concentrations of
pollutants from various nonpoint
sources, including atmospheric de-
position, street dirt accumulation,
and catchbasin and detention basin
sediment, were measured. Imperv-
ious sources (streets, sidewalks,
driveways, parking lots and roof-
tops) were found to contribute
more than 60% of the total runoff
flow when precipitation exceeded
0.1 inch. Street surfaces contrib-
uted 25% of the total flow in the
monitored sites. Most of the total
solids in urban runoff originated
from residential yards. Nutrients
were primarily detected in street
dirt samples, originating from vehi-
cle emissions. Only a small frac-
tion of the total particulate loadings
on the impervious surfaces were re-
moved by rain (15%). Large
particles were not effectively re-
moved, while about one-half of the
smallest particles (less than 50 mi-
crons) were washed off during
rains. These small particles were
not very abundant, but contained
high heavy metal and nutrient con-
centrations. Most of the settled par-
ticulate material in the storm drain-
age inlets and sewerage pipes was
not removed during observed
storms.
Several control practices were insti-
tuted as pilot projects to determine
their effectiveness: street sweeping,
catchbasin cleaning and detention
ponds. Intensive street sweeping (3
times per week) resulted in rapid
and significant decreases in street
surface suspended solids loadings,
from 110 g/curb-meter down to 55
g/curb-meter. This 50% reduction
in suspended solids loadings re-
sulted in a maximum 10% decrease
in metal loadings. The median
particle size also decreased signifi-
-------
cantly with intensive street clean-
ing. A regenerative air street
cleaner showed substantially higher
performance in removing the finer
street particles. It appears that
conventional street sweeping re-
moves the larger particles and
rain removes the smaller
particles; however, street sweep-
ing did not reduce loadings of
toxic compounds by more than
10%. Cleaning of storm drain-
age inlets and catch basin sumps
twice per year reduced the lead
and total solids runoff concentra-
tions by between 10 to 25%.
COD, nutrients and zinc were re-
duced by between five and ten
percent After an initial cleaning,
it appeared that almost a full year
was required for sediment to reach
a 'stable volume' in the storm drain
inlet structures. Only 60% of the
total available sump volumes in the
Kiel structures and catchbasins
ere used for detention of particu-
lates at the 'stable volume.' Small
detention basins (detention times of
30 minutes or less) did not have
any significant effect on urban run-
off quality but did reduce peak
flow rates by up to 60 percent. De-
tention basins should be carefully
located so increased flow rates do
not disturb critical habitat areas.
The final recommendation states
that if intensive street sweeping
was implemented along with semi-
annual catchbasin sediment re-
moval, urban runoff discharges for
most pollutants would be reduced
by as much as 25%. Though these
reductions are small, they may be
important in reducing the accumula-
tion of contaminated sediments in
smaller creek systems.
Milwaukee Harbor, Wisconsin
(Multiple Impacts)
Milwaukee Harbor is a freshwater reservoir-embayment of Lake
Michigan. The Milwaukee River is productive, and typically over-
saturated with oxygen, as it moves through the agricultural and
mixed land uses of the upper two-thirds of the watershed (Pitt,
1986). Upon reaching the deeper and slower moving, impounded
lower one-third of the watershed which includes the suburban
and urban areas of the city of Milwaukee, dissolved oxygen lev-
els plummet 5 to 6 mg/L resulting in periodic septic conditions.
Point source sewage treatment plant discharges are not import-
ant for this watershed because only 10% of the city's population
is served by sewage treatment plants that discharge into the
river. Water quality and quantity are monitored at 6 sampling sta-
tions along the river by the Milwaukee Sewerage District and the
U.S. Geological Survey.
The Ontario Ministry of the Environment, in cooperation with the
Wisconsin Department of Natural Resources, funded the applica-
tion of the Source Loading and Management Model (SLAMM)
which was used to predict the effectiveness of various stormwa-
ter runoff source area, sewerage, and outfall controls for urban
runoff fn the Milwaukee metropolitan area. Performance data on
control practices for reducing runoff flow volumes and lead dis-
charges were obtained from two study areas in Toronto, includ-
ing a mixed residential/commercial and a light/medium industrial
area. The data from the Toronto study were augmented with ex-
tensive literature information on the effectiveness of source area
and outfall urban controls. Control options analyzed using
SLAMM included: increased street cleaning, catchbasin clean-
ing, wet detention basins, infiltration of runoff from half of the
residential roofs currently draining to pavement, and combina-
tions of these practices. Cost effectiveness of the retrofits was
analyzed by examination of the cost per unit removal for sus-
pended solids, phosphorus, fecal coliform bacteria, and lead for
each of the control options.
Three cost-effective programs for stormwater runoff particulate
control were identified: 1) detention basins and detention basins
plus street sweeping at a cost of $2 to $3 per kg with a potential
maximum control of 26%; 2) partial infiltration plus large wet ba-
sins at $6 per kg with a maximum control potential of 44%; and 3)
all practices combined including increased street cleaning and
catchbasin cleaning, partial infiltration, and large wet detention
basins at $9 per kg with a maximum control level of 47%,
The most highly recommended program combined infiltration
and wet detention ponds. However, control program perfor-
mance varied for different land uses. The modeling effort further
revealed that the age of development as well as land use should
be considered in the evaluation of water quality and effective-
ness of controls.
-------
Dry ED Wet ED Siormwaier ED Wet Ponds Natural Pond/Wetland
Wetlands Wetlands Wetlands Systems
J
a
u
'G
U
00
Letiend
Reported removal efficiencies for
each management practice are vari-
able. To account for this variability
the box and whiskers representation
was used to display the range of the
reported values and to characterize
the distribution by indicating various
percentiles. It should be noted that
because of the limited data points,
no advanced statistical tests were
used to evaluate the significance of
the reported data. The box en-
closes 50% of the reported values,
with the lower and upper sides of
the box representing the 25th and
75th percentiles respectively. The
line inside the box represents the
median value of the distribution.
The horizontal whiskers above and
below the box, if any, indicate the
90th and 10th percentiles, respec-
tively. Extreme values, also called
outliers, if any, (higher than the 90th
or lower than the 10th percentiles)
are represented by circles.
Dry ED Wet ED Stormwaier ED Wet Ponds Natural Pond/Wetland
Wetlands Wetlands Wetlands Systems
Total Suspended Solids and Phosphorus Removal Capabilities
of Structural Stormwater Management Practices (MWCOG.1992)
Additional Examples of
Successful Urban and In-
dustrial Stormwater Con-
trol Practices
Metropolitan Washington
Council of Governments
This study, prepared as a part of the
Technical Guidance to implement
Section 6217(g) of the Coastal
Zone Act Reauthorization Amend-
ments, provides a comparative as-
sessment of various structural
Stormwater quality control prac-
tices (MWCOG, 1992). It analyzes
the capabilities and limitations of
eleven practices. The study thor-
oughly reviewed the existing litera-
ture, consulted with numerous local
and state experts around the coun-
try, and analyzed data from on-
going projects. The results of the
literature survey concerning the ef-
fectiveness of eleven Stormwater
management practices in removing
total suspended sediment and total
phosphorus presented in this study
are illustrated in the Figures above.
Although a wide range of removal
efficiencies for each practice was
observed, high removal rates were
achieved in a number of cases. The
maximum removal rates for total
suspended sediments ranged from
70% to more than 95%. The high-
est reported removals were
achieved by wet ponds, wet ex-
tended detention ponds, natural wet-
lands, and ponds/wetland systems.
-------
Wet Detention Ponds, Charlotte, NC
The performance of existing urban wet detention ponds in the City of
Charlotte within the piedmont region of North Carolina, was evalu-
ated based on a comprehensive data collection program (Wu, Hoi-
man, and Dorney, 1988). The hydrologic and water quality responses
of three wet ponds were characterized during storm water events.
The three ponds studied control a combined area of 437 acres. Al-
though initially designed and built for storm runoff control, the re-
sults of this study indicate wet ponds have significant capacity to im-
prove water quality.
Differences in removal efficiencies among the three ponds were at-
trfeuted In part to surface area ratios calculated based on pond sur-
face and subarea acreage. Observed removal of total suspended sol-
ids was consistently high (82-100%) for the pond with the highest
area ratio. The two heavy metals monitored in this study, zinc and
iron, were also consistently removed with an efficiency rate of about
80% in pond A (high surface area ratio), and 42% in pond B (low sur-
face area ratio). For total phosphorous and nitrogen the removal effi-
ciencies were inconsistent, attributable to the variable input from wa-
terfowl droppings in the ponds. Average removal efficiencies for
two of the ponds are shown In the Table below.
Removal Efficiency Achieved by Wet Detention Ponds
Constituent
% Removal
Pondl Pond 2
TSS
Nutrients
Metals
91
6-23
79-82
54
20-24
42-45
High removal efficiencies for total
phosphorus were also observed.
Apart from the extended wetlands
for which fewer data were obtained
from the literature survey, the high-
est removal efficiencies achieved
exceeded 60% for the other ten
practices. The highest removals
were achieved with wet extended
detention ponds, natural wetlands,
and pond/wetland systems. The
performance of existing urban wet
detention ponds was also examined
in a case study from Charlotte,
North Carolina (see inset above).
Illicit Connection Controls,
Michigan
Recent studies in Michigan have
recognized that development occur-
ring while undersized waste water
treatment plants are operating can
create wide-spread illicit connec-
tion problems. For example, the
Huron River Pollution Abatement
Program in Wastenaw County,
Michigan, inspected 660 busi-
nesses, homes, and other buildings
discharging stormwater to the Allen
Creek drain. Of the buildings in-
spected, 14% were found to have
improper storm drain connections,
with the highest percentage (60%)
for automobile related businesses.
Although some of the problems dis-
covered in this study resulted from
improper plumbing or illegal con-
nections, the majority were ap-
proved connections at the time they
were built Efforts are underway to
correct those illicit connections
identified during the inspection pro-
gram (40 CFR parts 122,123, and
124).
Combined Sewer Pollution Con-
trol: Structural Practices. Struc-
tural practices for controlling com-
bined sewer overflow pollution usu-
ally parallel conventional wastewa-
ter treatment practices. They are
designed to handle intermittent and
random flows which vary in magni-
tude and quality. These practices
include in-line storage, off-line stor-
age, storage sedimentation, swirl
concentrators, screens, dissolved
air floatation, high rate filtration,
treatment lagoons, contact stabiliza-
tion, rotating biological contactors,
and high rate trickling filters. They
all differ in costs, efficiencies, suit-
ability, and operation and mainte-
nance. Two case studies concern-
ing in-line storage and an inte-
grated approach follow.
In-iine Storage Control, Seattle
In-line storage control is a low capi-
tal cost method that uses existing
facilities. It is easily integrated
with dry-weather collection, treat-
ment, and disposal activities, and is
adaptable to future expansion. Met-
ropolitan Seattle implemented an
on-line storage control system to
mitigate Combined Sewer Over-
flows (CSO) impacts to receiving
waters (Finnemore, 1982). The sys-
tem performance was evaluated in
-------
terms of the reduction of overflow
volume, overflow frequency, and
annual reduction of pollutant loads.
The system was estimated to re-
duce overflow volume by 74%.
The resulting reductions in pollu-
tion loads were estimated to be
493,000kg/year of suspended sol-
ids, and 136,000kg/year of BOD.
The total costs for this system are
summarized as follows:
In-line Storage Control Costs
Regulators
Computer facilities
Engineering
O&M cost (per year)
$9,762,000
$5,717,000
$924,000
$440,000
Integrated Approach, Saginaw, Ml
Saginaw, Michigan uses a combina-
tion of storage and treatment pro-
cesses to take advantage of the ca-
pabilities of exisiting systems
(Finnemore, 1982). This integrated
approach reduces the volume of
overflows to receiving waters and
treats overflows that do occur to
near primary treatment levels. This
integrated system at the Hancock
Street facilities, includes: (1) in-
line storage; (2) using existing inter-
ceptor capacity controlled by modi-
fied regulator stations; (3) a flood
protection pumping station, an off-
line storage-treatment basin capa-
ble of treating and disinfecting all
overflows; and (4) a capability to
treat all flows retained in storage at
the local dry-weather treatment
plant. Together this system sup-
ports a city-wide plan to eliminate
uncontrolled combined sewer dis-
charge to the Saginaw River.
The performance of the Hancock
Street storage/treatment facility
was characterized using data from
the 1978 summer monitoring pro-
gram. Eleven storms occurred dur-
ing the monitoring period and an es-
timated 52,000,000 gallons were
pumped to the storage/treatment
basin. Forty percent of this volume
overflowed, after treatment, during
three storms. The overflow fre-
quency was reduced by 73%, and
the effectiveness of the basin in
treating the overflows ranged be-
tween 35% and 75% reduction in
concentrations of eight different
pollutants.
The total construction cost of the
Hancock Street CSO control facili-
ties was $7,280,000, including
modifications to the in-line storage
system (regulators) and the stor-
age/treatment facilities. Estimated
annual operating and maintenance
cost for the storage/treatment sys-
tem is about $50,000/yr.
Detention Ponds and Retention
Basins. The ability of wet deten-
tion ponds and retention basins to
remove pollutants from stormwater
has been extensively studied. Nu-
merous case studies have shown
that reductions in suspended sedi-
ments, nutrients, and heavy metals
are possible through the use of ei-
ther retrofitted stormwater basins
or detention ponds designed specif-
ically for water quality im-
provements. The following case
study reported variable reductions
in total suspended solids, metals,
and nutrients.
Urban Retention Ponds,
Orlando, FL
A three pond stormwater retention
system receiving stormwater from
a highway interchange in Orlando,
Florida, was investigated (Youssef,
Wanielista, and Harper, 1986). The
three ponds were interconnected by
way of a large culvert to allow overi
flow to other ponds when storm
runoff exceeds the design level.
The first receiving pond has an ap-
proximate surface area of 1.3 ha
(3.2 acres), an average depth of
1.5m (4.9 feet), and a total drainage
area of 10.8 ha (26.7 acres). The
ponds maintained a large standing
crop of filamentous algae virtually
year-round.
Field investigations conducted dur-
ing 1982-1984 were designed to as-
sess 1) the quantity of pollutants en-
tering the pond, 2) the average
water quality parameters in the
basin water, 3) the accumulation of
nutrients and heavy metals in the
sediment of the pond, and 4) the
leaching of heavy metals to the
groundwater beneath the retention
ponds.
The removal efficiencies of
late metals were found to range
from 77% for copper to over 95%
for lead and zinc, while the re-
moval of the dissolved fraction was
only about 50% for lead and cop-
per and 88% for zinc. The removal
of paniculate phosphorus and or-
ganic nitrogen was, on the other
hand, poor and did not exceed
12%. The removal of the dissolved
fraction of nutrient loadings ranged
from 81.6% for ammonia to 90%
for phosphorus.
Accumulation of phosphorus in the
bottom sediment of the pond was
evaluated at 99% of the total input
during a 7 year period. However,
85-90% removal of the total nitro-
gen load was attributed to nitrifica-
tion-denitrification processes. The
removal of paniculate heavy metals
from the pond water was also attrib-
uted to settling and accumulation in
-------
Constructed Wetlands for Wastewater Treatment
DUST Marsh Trap Efficiencies (percent)
Constituents System A System B System C" Overall"
TDS
TSS
BOOs
NHa-N
NQj-N
TKN
Orthophosphate
Total phosphate
Chromium (Cr)
Copper (Cu)
Lead (Pb)
Manganese (Mn)
Nickel (Ni)
Zinc(Zn)
-9
42
-26
-22
9
7
53
17
40
5
30
-22
34
6
-20
24
-22
27
5
-32
19
-44
20
-10
27
-1
-30
-22
-50
45
-8
12
8
-17
28
51
53
32
83
-86
12
51'
-49
64
-35
10
15
-28
56
48
68
31
88
-111
20
33
"System C inflow = composite of System A and B outflows.
Overall trap efficiencies may be greater than cumulative reductions by individual systi
because System C provides secondary treatment for System A and B discharges
'ems
the bottom sediment within a rela-
tively short distance from the
stormwater inlet
One common concern of using re-
tention basins is the potential for
groundwater contamination. How-
ever, monthly groundwater samples
revealed no conclusive evidence of
heavy metals migration from the
pond.
Stormwater Wetlands,
Fremont, CA
This study summarizes the results
from the Demonstration Urban
Stormwater Treatment (DUST)
marsh project at Coyote Hills in
Fremont, California (Meiorin,
1986). The study analyzes the ap-
plicability of artificial wetlands as a
means for improving urban
stormwater quality. The wetland
system and control structures con-
sist of a series of detention basins
designed to simulate a secondary
kwastewater treatment plant, includ-
ing pretreatment, clarifier, and bio-
logical processes. The basins were
built in 1983 to receive water from
approximately 4.6 square miles in-
cluding residential, commercial,
and open areas as well as urban
roads.
A monitoring program during the
wet seasons of 1984 and 1985 docu-
mented the marsh development and
treatment effectiveness. Samples
from eleven storms collected from
each basin outflow were analyzed
and the results, expressed in terms
of trap efficiency, are listed in the
table above.
The overall trap efficiency for
heavy metals (chromium, copper,
nickel, lead, and zinc) ranged from
20-88%, due in part to settling of
heavy suspended particles. Nitro-
gen is transported into the marsh
primarily as ammonia and organic
nitrogen and was moderately
trapped due to plant uptake and ad-
sorption into the sediment. How-
ever, a higher trap efficiency was
seen for phosphorus (orthophos-
phate and total phosphate).
Heavy metal concentrations in veg-
etation generally followed a pattern
of greatest relative uptake occur-
ring in plant roots with decreasing
levels in the leaf and seed tissues.
Generally soil-root concentrations
were less than half of those found
in the surface soil, leaf and seed
concentration were one-half to one-
fourth of the root amount.
Bioaccumulation of chromium, cop-
per, lead and zinc in fish tissue ex-
ceeded the 85% Elevated Data
Level (EDLa) in all the basins;
however, bioaccumulation of cad-
mium, nickel and selenium was not .
significant. Further research was
recommended to determine the
long-term build-up of heavy metals
and toxic hydrocarbons in the
foodchain.
It should be noted that the results
of this study were collected from a
relatively new wetland system, and
the uptake of nutrients and heavy
metals could vary as the system ma-
tures.
Sand Filters, Delaware
The State of Delaware developed a de-
sign approach for implementation of
stormwater management water quality
control practices targeting urban areas
having little or no pervious area
(Shaver, 1991). The controls were
adopted under the urban stormwater
runoff component of the NPDES pro-
gram. The State of Delaware enacted
an urban stormwater control program
focussing on new construction. After
July 1, 1991 all new development
activities require reviews for water
quality impacts prior to their ap-
proval. The program requires that
pre-development peak discharges
"Statistical values developed by the California Fish and Game from the 1984 Toxic Substances Monitor-
ing program indicating percent ofexceedance of a toxic substance in observed fish tissues.
-------
are not exceeded and water quality
is protected by vegetative and struc-
tural control strategies designed to
remove 80% of the inflow's sus-
pended solids. Shallow stormwater
management ponds that encourage
plant growth are preferred because
nutrients are a significant source of
water quality degradation in Dela-
ware. Often spatial or other engi-
neering considerations limit the use
of ponds in urban areas. In heavily
urbanized areas, sand filters may be
appropriate for both new develop-
ment and retrofits as they do not
limit land usage. The sand filters
will be designed to treat runoff
from frequent storm events, i.e., the
first inch of rainfall. The design
procedures for the sand filters are
based on equations developed by
the City of Austin as well as struc-
tural design previously used for a
project in the State of Maryland.
Filter efficiency is related to the
distribution of pollutants in the
various particle size classes.
Most of urban paniculate matter
is of a coarser size fraction; how-
ever, most of the other pollutants
(except for metals which tend to be
more evenly distributed across the
size classes) are associated with the
smaller particle sizes. For exam-
ple, approximately 6% of urban par-
ticulate matter is in the silt and clay
soil size range; but silts and clays
contain more than 50% of the phos-
phorus. The sedimentation cham-
ber of the filtration system is de-
signed to remove the sand and
gravel components and the sand fil-
ter is designed to remove the finer
silt and clay particles. The deten-
tion chamber provides a detention
time sufficient to remove sand and
coarse particles based on their cal-
culated settling velocities. The fil-
ter drains the first inch of runoff
within a 24 hour period by assum-
ing an average filtration rate of
0.04 gal/min/ft for the sand. The
design drainage area, typically a
parking lot, must be less than 5
acres. Predicted removal efficien-
cies are 70% removal of total sus-
pended solids, 33% removal of
total phosphorus, 21% removal of
total nitrogen, and 45% removal of
the metals lead and zinc. Actual re-
movals contained in the Austin re-
port are somewhat higher than ex-
pected. Removal efficiencies re-
ported in several sources (Wood-
ward-Clyde, 1991) are illustrated in
the following Figure. For example,
the 25th and 75th percentile of TSS
removal by filtration systems were
about 70 and 90 percent, respec-
tively. The median value is about
82 percent.
100
0)
'3
« £3
^ O
20
0
TSS
TP
TN
Pb
Removal efficiencies for total suspended solids, total phosphorous,
total nitrogen, lead, and zinc by sandfilter basins.
-------
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