United States
Environmental Protection
Agency
Office of Water
(4606)
EPA816-F-01-020
July 2001
oEPA Source Water Protection
Practices Bulletin
Managing Storm Water Runoff to
Prevent Contamination of
Drinking Water
Storm water runoff is rain or snow melt that flows off the land, from streets, rooftops, and
lawns. The runoff carries sediment and contaminants with it to a surface water body or
infiltrates through the soil to ground water. This fact sheet focuses on the management of
runoff in urban environments; other fact sheets address management measures for other
specific sources, such as pesticides, animal feeding operations, and vehicle washing.
SOURCES OF STORM WATER RUNOFF
Urban and suburban areas are predominated by impervious cover including pavements on roads,
sidewalks, and parking lots; rooftops of buildings and other structures; and impaired pervious
surfaces (compacted soils) such as dirt parking lots, walking paths, baseball fields and suburban
lawns.
During storms, rainwater flows across these impervious surfaces, mobilizing contaminants, and
transporting them to water bodies. All of the activities that take place in urban and suburban
areas contribute to the pollutant load of
storm water runoff. Oil, gasoline, and
automotive fluids drip from vehicles onto
roads and parking lots. Storm water runoff
from shopping malls and retail centers also
contains hydrocarbons from automobiles.
Landscaping by homeowners, around
businesses, and on public grounds contributes
sediments, pesticides, fertilizers, and
nutrients to runoff. Construction of roads and
buildings is another large contributor of
sediment loads to waterways. In addition,
any uncovered materials such as improperly
stored hazardous substances (e.g., household
cleaners, pool chemicals, or lawn care
products), pet and wildlife wastes, and litter can be carried in runoff to streams or ground water.
Illicit discharges to storm drains (e.g., used motor oil), can also contaminate water supplies.
Storm water is also directly injected to the subsurface through Class V storm water drainage
wells. These wells are used throughout the country to divert storm water runoff from roads,
roofs, and paved surfaces. Direct injection is of particular concern in commercial and light
industrial settings (e.g., in and around material loading areas, vehicle service areas, or parking
lots).
Parking lot runoff
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WHY IS IT IMPORTANT TO MANAGE STORM WATER RUNOFF NEAR THE
SOURCES OF YOUR DRINKING WATER?
Impervious areas prohibit the natural infiltration of rainfall through the soil, which could filter
some contaminants before they reach ground water. Also, impervious surfaces allow the
surface runoff to move rapidly. Development reduces the amount of land available for
vegetation, which can mitigate the effects of rapid runoff and filter contaminants. When the
percentage of impervious cover reaches 10 to 20 percent of a watershed area, degraded water
quality becomes apparent.
There are three primary concerns associated with uncontrolled runoff: (1) increased peak
discharge and velocity during storm events resulting in flooding and erosion; (2) localized
reduction in recharge; and (3) pollutant transport.
When runoff is confined to narrow spaces,
such as streets, the velocity at which water
flows increases greatly with depth. This
contributes to erosion in areas without
vegetation cover, increased flooding in low
lying areas, and sedimentation in surface
water bodies. Sediment deposited in streams
can increase turbidity, provide transport
media for pathogenic bacteria and viruses,
and decrease reservoir capacity. Sediments
also smother aquatic species, leading to
habitat loss and decreased biodiversity of
aquatic species. The fast-running runoff is not afforded an opportunity to infiltrate into the
subsurface, and ground waters are not recharged by rain events.
EPA considers nonpoint source pollution, including storm water runoff, to be one of the most
important sources of contamination of the nation's waters. According to a nationwide study, 77
of 127 priority pollutants tested were detected in urban runoff. Some of the principal
contaminants found in storm water runoff include heavy metals, toxic chemicals, organic
compounds, pesticides and herbicides, pathogens, nutrients, sediments, and salts and other de-
icing compounds. Some of these substances are carcinogenic; others lead to reproductive,
developmental, or other health problems that are associated with long-term exposure.
Pathogens can cause illness, even from short-term exposure, that can be fatal to some people.
Urban runoff is commonly collected in storm sewers and
discharged to waterways untreated, so that any contaminants
carried by the storm water are discharged to surface water
bodies that are used as the sources of drinking water. In
addition, about 20 percent of the population in the U.S. is
served by combined sewer systems (for both sanitary waste
and storm water) that, during heavy storm events, allow
contaminants from sanitary sewage to discharge directly to
waterways untreated.
AVAILABLE PREVENTION MEASURES TO ADDRESS STORM WATER
RUNOFF
A variety of management practices, including pollution prevention and treatment devices, are
available to abate storm water pollution. The most effective storm water pollution prevention
plans combine these measures and reflect local soil, precipitation, and land use conditions. Some
of the more widely-used management measures are described below.
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Please keep in mind that individual prevention measures may or may not be adequate to prevent
contamination of source waters. Most likely, individual measures should be combined in an
overall prevention approach that considers the nature of the potential source of contamination,
the purpose, cost, operational, and maintenance requirements of the measures, the vulnerability
of the source waters, the public's acceptance of the measures, and the community's desired
degree of risk reduction.
Pollution source control and prevention measures include public education to homeowners and
business owners on good housekeeping, proper use and storage of household toxic materials,
and responsible lawn care and landscaping; storm drain stenciling; hazardous materials
collection; and eliminating illicit discharges. The incorporation of best management practices
(BMPs) in building and site-development codes, if feasible, should be encouraged. On roadways,
proper maintenance of rights-of-way, control of chemical and nutrient applications, street
cleaning or sweeping, storm drain cleaning, use of alternative or reduced de-icing products, and
equipment washing can reduce the pollutant content of runoff.
Without appropriate erosion and sedimentation control (ESC) measures, construction
activities can contribute large amounts of sediment to storm water runoff. Erosion can be
controlled by planting temporary fast-growing vegetation, such as grasses and wild flowers.
Covering top soil with geotextiles or impervious covers will also protect it from rainfall. Good
housekeeping measures for construction sites include construction entrance pads and vehicle
washing to keep sediment and soil on-site. Construction should be staged to reduce soil
exposure, or timed to coincide with periods of low rainfall and low erosion potential, such as in
the fall, rather than during spring rains. Other measures include sediment traps and basins;
sediment fences; wind erosion controls; and sediment, chemical, and nutrient control.
If available, ordinances and regulations on construction activities can require plan reviews to
ensure that erosion during construction is minimized or require ESC measures during
construction. Inspections of ESC measures and repair of controls where needed will maintain
the working order of these controls and maximize their benefit.
Local governments can use a variety of land use controls to protect source water from
potential contamination. For example, subdivision controls help to ensure that expected
development will not compromise drinking water quality or ground water recharge. Requiring
proper storm water management in new developments and redevelopments will ensure that
runoff does not become excessive as areas of paved surfaces increase. Low impact
development incorporates maintaining pre-development hydrology, considering infiltration
technology, and re-routing water to recharge the aquifer.
Minimizing directly connected impervious areas
(DCIAs) is important to reducing the flow and volume of
runoff. Planners should direct runoff from roofs,
sidewalks, and other surfaces over grassed areas to
promote infiltration and filtration of pollutants prior to
surface water deposition. Porous design of parking lots
also provides places for storm water to infiltrate to soils.
Concrete grid pavement is typically placed on a sand or
gravel base with void areas filled with pervious materials
such as sand, gravel, or grass. Storm water percolates
through the voids into the subsoil. Planting landscaped •.
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areas lower than the street level encourages drainage. .,:«„,„«.>,,.>,»•««,.
Concrete grid pavement
Structural designs are used to control runoff or temporarily store storm water on site. A
number of structural devices have been developed to encourage filtration, infiltration, or settling
of suspended particles. Some of the more commonly-used practices are described below.
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Grassed swales are shallow, vegetated ditches that reduce the speed and volume of runoff.
Soils remove contaminants by infiltration and filtration. Vegetation, or turf, prevents soil erosion,
filters out sediment, and provides some nutrient uptake. Maintenance of grassed swales involves
regular mowing, re-seeding, and weed control, along with inspections to check for erosion and
ensure the integrity of the vegetative cover. To function properly, the inflow to the swale must
be sheet flow from a filter strip or an impervious surface (i.e., not from the end of a pipe).
Swales have demonstrated solids removals exceeding 80 percent. Apart from grassed swales,
grassed waterways (wide, shallow channels lined with sod) are often used as outlets for runoff
from terraces.
Buffer strips are combinations of trees, shrubs, and grasses planted parallel to a stream. Buffer
strips should consist of three zones—about four or five rows of trees closest to the stream, one
or two rows of shrubs, and a 20 to 24 foot wide grass zone on the outer edge. They decrease
the velocity of runoff, thus moderating flooding and preventing stream bank erosion. The
vegetation and soils also strain and filter sediments and chemicals. Buffer strips should be
maintained by controlling weeds and mowing grasses once or twice annually. In the long term,
each zone should be harvested and replanted. About 10 to 20 percent removal of solids has
been demonstrated in buffer zones. These buffer strips, however, do not necessarily increase
infiltration.
Filter strips are areas of
close-growing vegetation on gently
sloped land surfaces bordering a
surface water body. They work by
holding soils in place, allowing some
infiltration, and filtering solid particles
out of the runoff from small storms.
Plants with dense root systems are
preferred; the ideal species and mixes
of vegetation are specific to the
region. The width and length of the
filter strip depends on the size and
grade of the slope it drains.
Maintenance activities include
inspections, mowing, and removal of
sediment build-up. Filter strips can remove nitrogen and phosphorus, but are less effective in
filtering pesticides. They are most effective when water flow is even and shallow and if grass
can regrow between rains.
Storm water ponds (wet ponds) consist of a permanent pond,
where solids settle during and between storms, and a zone of
emergent wetland vegetation where dissolved contaminants
are removed through biochemical processes. Wet ponds are
usually developed as water features in a community,
increasing the value of adjacent property. Other than
landscape maintenance, only annual inspection of the outlets
and shoreline is required. Vegetation should be harvested
every 3 to 5 years, and sediment removed every 7 to 10 years.
Wet ponds can achieve 40 to 60 percent phosphorus removal and 30 to 40 percent total nitrogen
removal.
Filter strip
Storm water pond
Constructed wetlands are similar to wet ponds, with more emergent aquatic vegetation and a
smaller open water area. Storm water wetlands are different from natural wetlands in that they
are designed to treat storm water runoff, and typically have less biodiversity than natural
wetlands. A wetland should have a settling pond, or forebay, if significant upstream soil erosion
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is anticipated. Coarse particles remain trapped in the forebay, and maintenance is performed on
this smaller pool. Wetlands remove the same pollutants as wet ponds through settling of solids
and biochemical processes, with about the same efficiency. Maintenance requirements for
wetlands are similar to those of wet ponds.
Infiltration practices (basins and trenches) are long,
narrow stone-filled excavated trenches, 3 to 12 feet deep.
Runoff is stored in the basin or in voids between the
stones in a trench and slowly infiltrates into the soil matrix
below, where filtering removes pollutants. Infiltration
devices alone do not remove contaminants, and should be
combined with a pretreatment practice such as a swale or
sediment basin to prevent premature clogging.
Maintenance consists of inspections annually and after
major rain storms and debris removal, especially in inlets
and overflow channels. Infiltration devices and
associated practices can achieve up to 70 to 98 percent
contaminant removal.
Swirl-type concentrators are underground vaults infiltration basin
designed to create a circular motion to encourage
sedimentation and oil and grease removal. The currents rapidly separate out settleable grit and
floatable matter, which are concentrated for treatment, while the cleaner, treated flow
discharges to receiving waters. Swirl concentrators have demonstrated total suspended solids
and BOD removal efficiencies exceeding 60 percent.
BMPsfor Class V storm water drainage wells address siting, design, and operation of these
wells. Siting BMPs for storm water drainage wells include minimum setbacks from surface
waters, drinking water wells, or the water table. Storm water drainage wells may also be
prohibited from areas of critical concern, such as source water protection areas, or from areas
where the engineering properties of the soil are not ideal for their performance. Available
design BMPs for storm water drainage wells include sediment removal devices (such as oil/grit
separators or filter strips), oil and grease separators, and pretreatment devices such as
infiltration trenches or wetlands (described above). Maintenance of these BMPs is crucial to
their proper operation. Management measures related to operation include spill response,
monitoring, and maintenance procedures. Source separation, or keeping runoff from industrial
areas away from storm water drainage wells, involves using containment devices such as berms
or curbs (see the fact sheets on vehicle washing and small quantity chemical use for more
information on these devices).
EPA's National Pollutant Discharge Elimination System (NPDES) Permitting Program
regulates storm water runoff from municipal separate storm sewer systems (MS4s) and
industrial activity (including construction). The current rules establish permit requirements for
more than 5,000 MS4s nationwide. NPDES storm water permits issued to MS4s require these
MS4s to develop the necessary legal authority to reduce the discharge of pollutants in storm
water to the maximum extent practicable and to develop and implement a storm water
management program that includes:
• Structural and source control measures to reduce pollutants from runoff from
commercial and residential areas, including maintenance, monitoring, and planning
activities;
• Detection and removal of illicit discharges and improper disposal into the storm sewer;
• Monitoring and control of storm water discharges from certain industrial activities; and
• Construction site storm water control.
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In addition, the storm water rule for certain small MS4s requires post-construction storm water
management controls. These local controls are in addition to existing federal regulations that
require NPDES permits of all construction activities disturbing greater than one acre.
Recently, EPA developed a menu of BMPs that provides more than 100 fact sheets on
measures that small MS4s could use to control urban storm water runoff. The menu is available
from EPA's Web site at www.epa.gov/npdes.
FOR ADDITIONAL INFORMATION
These sources contain information on storm water management measures. All of the documents
listed are available for free on the Internet. State departments of transportation or agriculture,
whose contact information can be found on the Internet or in the phone book, are also good
sources of information.
To pass local ordinances or regulations to affect storm water controls, contact city or county
public works departments, zoning offices, permitting offices, or transportation departments, who
typically have the authority to pass local ordinances. Contact local government authorities in
your area to see if there are ordinances in place to manage storm water. Numerous examples
of local source water protection-related ordinances for various potential contaminant sources
can be found at http://www.epa.gov/r5water/ordcom/,
http://www.epa.gov/owow/nps/ordinance/, and
http://www.epa.gov/owow/nps/ordinance/links.htm.
The following resources provide information on selection and design of specific management
measures:
The Center for Watershed Protection's Stormwater Manager's Resource Center
(www.stormwatercenter.net) provides technical assistance storm water management issues.
Northern Arizona University offers a course on wet weather flow management, materials are
available at http://jan.ucc.nau.edu/~dmh3/egr499/.
Texas Nonpoint SourceBOOK (www.txnpsbook.org) contains four manuals on storm water
Best Management Practices, including "Urban Nonpoint Source Management," and an
interactive BMP selector.
U.S. EPA, Office of Ground Water and Drinking Water. (September 1999). The Class V
Underground Injection Control Study. Volume 3: Storm Water Drainage Wells. EPA/816-
R-99_014c. Retrieved May 2, 2001, from the World Wide Web:
http://www.epa.gov/safewater/uic/classv/stw-fact.pdf
U.S. EPA, Office of Science and Technology. (August 1999). Preliminary Data Summary of
Urban Stormwater Best Management Practices. EPA-821-R-99-012. Retrieved February 7,
2001, from the World Wide Web: http://www.epa.gov/OST.
U.S. EPA, Office of Wastewater Management. (September 1992). Storm Water Management
for Industrial Activities: Developing Pollution Prevention Plans and BMPs. Retrieved
February 6, 2001, from the World Wide Web: http://www.epa.gov/owm/sw/indguide/index.htm
U.S. EPA, Office of Wetlands, Oceans, and Watersheds. (January 1993). Guidance
Specifying Management Measures for Sources of'Nonpoint Pollution in Coastal Waters.
EPA-840-B-93-001c. Retrieved February 15, 2001, from the World Wide Web:
http ://www.epa.gov/OWOW
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Washington State Department of Transportation. (February 1995). Highway Runoff Manual.
M 31-16. Retrieved February 15, 2001, from the World Wide Web:
http://www.wsdot.wa.gov/fasc/engineeringpublications/manuals/highway.pdf
Wyoming Department of Environmental Quality. (February 1999). Urban Best Management
Practices for Nonpoint Source Pollution. Draft. Retrieved February 21, 2001, from the World
Wide Web: http://deq.state.wy.us/wqd/urbbmpdoc.htm
University extension services are excellent sources for information on water quality issues,
including storm water management. The Oregon Department of Agriculture offers
comprehensive list of links to many of these on its Web site
(http://www.oda. state.or.us/Natural_Resources/wq_ces.htm).
Following are examples of extension services that offer fact sheets on a variety of storm water
management measures, including best management practices:
Iowa State University Extension (http://www.extension.iastate.edu/Pages/pubs/).
North Carolina Cooperative Extension Service (http://www.ces.ncsu.edu/resources/).
Oklahoma State University. Division of Agricultural Sciences and Natural Resources
(http://agweb.okstate.edu/pearl/wqs).
Purdue University Cooperative Extension Service
(http://www.agcom.purdue.edu/AgCom/Pubs/menu.htm).
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