United States
Environmental Protection
Agency
Oflice of
Water Program Operations
(WH-546)
Washington, D.C. 20460
The
Hidden Dangers
of Urban
Stormwater
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What is Urban Stormwater?
Rainfall in the city brings welcome relief from air
pollution, summer heat and everyday urban grime.
Stormwater not only launders the air, but washes
unsightly debris from streets and sidewalks. After a
rainfall, nature presents us with a sparkling clean
environment, temporarily free of noxious gases and dirt
particles. Each cycle repeats itself, dry periods
accumulate dirt and pollutants, then rain washes them
away—a natural pollution control process, or so it would
seem. In reality, Stormwater merely transfers street
surface contaminants to urban waterways. What is
washed from St. Louis streets may turn up in New
Orleans drinking water.
Clogged catch basin during an
urban downpour.
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Nonpoint source pollutants;
what are they and
where do they come from?
Generally speaking, most people think of urban pollution
as belching smokestacks, auto exhaust and industrial
drainage, all of which originate from an identifiable
source and can be controlled at that source.
Technically, these pollutants are identified as coming
from point sources, places that literally can be pointed
to. Stormwater, because it collects pollutants from a
wide area, is designated as a nonpoint source. Though
much less obvious, it can be equally as hazardous.
Invisible microscopic pollutants including lead, mercury.
cadmium, zinc, copper, chromium, other toxic
substances, and organic matter lie dormant on city
streets along with ordinary dirt. The first heavy rainfall
discharges them into a combined sewer system which,
more often than not, overflows spewing sewage and
urban runoff alike into the city's waterways.* Once in a
river or other body of water, these organic substances
degrade, depleting oygen and suffocating aquatic life.
The origins of these substances can be traced to:
• Airborne contaminant fallout, both manmade and
natural; including unfiltered smokestack debris, coal
dust incinerator particles, wind blown dirt and other
substances.
Meteorological fallout common Traffic congestion on a typical
in most large American cities, urban multilane highway.
Trash buildup resulting from a
poorly managed trash removal
program.
*Direct discharges of runoff by separate sewer systems have
similar effects on receiving waters. Although separate storm sewer
systems overflow into rivers, lakes, and streams, they only
discharge Stormwater. They do not combine with the sanitary
sewage systems in spilling untreated wastes into waterways during
heavy rainfall.
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Developing areas are
characterized by construction
activity. Sediment from these
sites contributes to pollution of
stormwaters,
• Traffic related pollutants from autos including lead,
zinc, barium, magnesium and sodium from oil; asbestos
from brake and clutch linings; cadmium, carbon black,
nitrogen compounds from tires; other substances.*
• Public refuse, overflowing trash and general street
debris containing microscopic pollutants.
Not all nonpoint source pollutants come from air,
traffic and refuse. Sedimentation, a more visible form of
pollution, often comes from construction erosion in
developing areas and surface runoff in already
developed areas. Erosion occurs when land is cleared of
its natural vegetative cover and exposed to heavy
rainfall. Each raindrop wears away a little dirt until tiny
rills are formed in the earth. The rills can become gullies
and even canyons, all the while transferring valuable top
soil to nearby waterways. Recent studies indicate that
this sediment can adsorb heavy metals, pesticides,
nutrients, and toxic elements, further compounding the
sediment problem.
Surface runoff is a major problem in urban areas
because so much of a city's land is covered by buildings
or pavement. The pavement channels stormwater,
which would otherwise be soaked up by soil and
vegetation, and pours it into streams and rivers causing
bank erosion, sedimentation, and destabilized stream
beds.
Industrial paniculate matter
bellowing from smokestacks.
*U.S. automobiles emit over 10 million tons of these and other
pollulants on the streets every year.
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How does stormwater runoff compare with
other forms of pollution?
The true dimensions of urban stormwater runoff become
clear when compared to industrial and municipal
sources (see charts below).
URBAN RUNOFF
1 To see how serious the urban runoff problem is, it should be
compared with the two other major contributors of water
pollution... industrial point and municipal point sources.
2 This chart compares the three sources on a national level with no
growth. Keeping in mind that the Federal Water Pollution Control
Act Amendments of 1972 require improved treatment at the point
sources, we can predict a trade-off point in the early 1980's. By that
time, industrial and municipal point sources will have curtailed their
share of water pollution. But urban runoff, proceeding unchecked,
will equal that from municipal point sources.
3 The magnitude of the urban runoff problem can be demonstrated in
yet another way. Here urban runoff is compared with combined
sewers, and secondary or advanced treatment in the amount of
suspended solids released into our streams. The lion's share of
pollutants comes from urban runoff.
4 Projected to 1990, the difference between urban runoff and the two
other sources is even greater.
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To clean up the nation's
waterways, most sewage
treatment plants such as this
one on the Potomac River at
Blue Plains. Washington, D.C.,
must be expanded and new
plants must be built. EPA has
pledged billions of dollars In the
1970's to assist local
communities in purifying their
rivers and lakes.
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BMP: A SUM OF MANAGEMENT TECHNIQUES
MANAGEMENT
OF RUNOFF
DETENTION BASINS
POROUS PAVEMENTS
RECREATION LAKES
MANAGEMENT
OF EROSION
SODDING
HAY BALES
SEDIMENT BASINS
MANAGEMENT
OF SOURCES
STREET CLEANING
CATCH BASIN
CLEANING
SEWER FLUSHING
WASTE PtCKUP
RESULTS
POLLUTANT
LOAD
REDUCTION
MINIMUM OF
OVERFLOWS
REDUCED
EROSION
ENHANCED
RECREATION
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What can be done about Urban Stormwater?
Clockwise—mechanized trash
removal, catch basin cleaning,
street sweeping, and detention
basin with riser pipe.
Today, the available options range anywhere from doing
nothing to catching the stormwater, storing it, and
channeling it through greatly expanded treatment
facilities.
Doing nothing only-neglects the problem until our
waterways become open sewers, devoid of clean water
and aquatic life.
On the other hand, treating stormwater is costly—
current price tag estimates range from 54 to 400 billion
dollars prohibitive for any budget.*
There is, however, another option, an alternative
which not only doesn't require extreme measures, but
offers a relatively low cost approach to Stormwater
Management. It is simply a modified version of present
urban maintenance programs commonly referred to as
municipal sanitary departments' Best Management
Practices (BMPS).
Best Management Practices may be divided into two
groups: those most useful for existing or developed
areas and those more applicable to new and developing
areas. Runoff problems in developed areas occur in
locations that have large concentrations of impervious
surface where drainage is accomplished primarily
through sewers. It is in these densely populated
commercial and industrial regions that BMPS are most
effective since they reduce the amount of pollutants that
enter the drainage system.
Developing areas, since they have limited surface
cover, can best utilize preventive approaches and
stormwater drainage occurs naturally through the
remaining areas porous soil. It is in these zones that the
greatest flexibility and proper application of BMPS can
help to prevent long-term stormwater erosion and
pollution.
Best Management Practices need not be complex
and can be implemented by most cities on a wide scale.
In some cases, BMPS are merely modified versions of
present urban maintenance programs and simply mean
adjustments in traditional street sweeping, catch basin
cleaning, trash removal and erosion control duties.
For example: street sweeping could increase to
maximize dirt removal potential and efficiency.
Catch Basin cleaning could be performed on a set
timetable as opposed to the present "as needed" basis.
*1976 EPA. needs survey estimate.
8
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An urban waterway just after a
summer storm.
Trash removal schedules could be increased to
prevent excess debris from being washed away and
clogging storm sewers.
Finally, cities can enact and enforce an erosion
prevention program through laws requiring:-
A. Detention facilities which hold sediment laden
stormwater until particles settle out naturally.
B. Use of straw bales and sandbags to filter out soil
particles,
C. Vegetative ground cover to reduce erosion while
improving appearance.
The Environmental Protection Agency believes that
through planning agencies set up by the Clean Water
Act each community can design a stormwaler pollution
control program best suited to its individual needs. Thus,
it is possible for cities to integrate their present services
with BMPS to develop an economical, yet effective,
approach toward reducing stormwater pollution. EPA's
approach involves assistance to State, city and local
governments in developing their own urban stormwater
runoff program.
What are the objectives of the Urban
Stormwater Program?
The overall objectives of Nationwide Urban Runoff
Program are to determine which areas in the country
have Stormwater Management problems, and provide
them with technical assistance best suited to their
needs.
Present EPA strategy will:
A. Help define the pollution problem as well as
establish priorities and direct resources.
B. Increase the flexibility of each city's options in
dealing with different pollution problems.
C. Improve present water quality management
agency coordination with planning, utilizing local
pollution reduction resources.
D. Develop a general permit program which will be
very broad initially but will become more specific as
knowledge about stormwater pollution increases.
What is actually known about
Urban Stormwater?
This pamphlet has attempted to briefly define Urban
Stormwater, its probable causes and measures that can
be taken to minimize its negative effect on our
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The City of Pittsburgh and its
golden triangle fountain of
sparkling wafer.
environment. Despite this knowledge, however, a
number of unknowns still remain. The most common
being: How much of these pollutants actually
accumulate on the streets? How much of that figure
really flows into the waterways? What impact will BMPS
have in reducing pollutant levels? Although solutions to
these unknowns are being developed, precise answers
are still in their embryonic stage and must evolve in a
methodical, step by step manner.
What can citizens do to increase
public awareness?
Concerned citizens, especially those acting through
voluntary organizations, can contribute to wiser
management of Urban Stormwater, They can inform the
public about its dangers and encourage appropriate
action to be taken. Citizens can also find out what the
situation is in their own area:
To what extent is street sweeping, catch basin
cleaning, and trash removal being utilized.
Are there laws governing sedimentation and
erosion?*
Since rainfall is essential and we don't live in a sterile
environment, some stormwater pollution is inevitable. It
is up to each citizen to increase public recognition of not
only the potential hazards of Urban Stormwater, but the
methods available to control its effect on our
environment.
"City of Bellevue, Washington has a strict erosion control ordinance
which has the power to halt contruction projects when BMPS are
not used and erosion occurs.
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