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Nonpoint Source Pollution
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In
Carrollton, polluted runoff that enters a storm drain
flows directly into our ponds or creeks, and onto the
Trinity River without treatment. |
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According to
a 1998 EPA report, about 40% of assessed U.S.
streams, lakes and estuaries were not clean enough
to support uses such as fishing and swimming. Leading
pollutants in impaired waters include silt, bacteria,
nutrients and toxic metals. Runoff from agricultural
lands and urban area are the primary sources of these
pollutants. Although the U.S. has made significant
progress in cleaning up polluted waters over the past 30
years, much remains to be done to restore and protect
the Nation's waters. For more information see the
National Water Quality Report. |
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At
least 50% of water quality problems in the United
States result from nonpoint source pollution. NPS
pollution occurs when water runs over the land, picks up
pollutants from dispersed sources - lawns, streets,
construction sites, farms - and transports them to
surface waters. |
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Impervious
surfaces, such as roads, rooftops, and parking lots
generate nine times more runoff than a wooded
area of the same size. The porous and varied terrain of
natural landscapes, like forests, wetlands, and
grasslands, trap rainwater and allow it to slowly filter
into the ground. In contrast, urban landscapes coat the
land with nonporous surfaces - which act like
impenetrable barriers to rainfall. Water remains above
the surface, accumulates, and runs off in large amounts
collecting contaminants on along its path to the nearest
storm drain. |
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Runoff from
a typical U.S. city during the first hour of a storm can
carry more pollutants than the city's untreated
sewage flow during the same period of time.
(Source: Urban Runoff and Stormwater Management
Handbook, EPA, 1990) |
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One of the
most common pollutants found in urban waterways is
detergent. The detergents destroy the external slime
coating of fish, which serves to protect them from
bacteria and parasites. Most fish die when the detergent
concentrations reach 15 parts per million. |
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One quart of oil can
contaminate up to 250,000 gallons of drinking water;
4 quarts of oil can form an oil slick approximately 8
acres in size. That's an oil sheen about the size of 8
football fields.
(Source: University of
Maryland Cooperative Extension Service, 1987) |
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Erosion
rates from natural areas, such as from an undisturbed
forest, are typically less than one ton/acre/year, while
erosion from construction sites ranges from 7.2 to
over 1,000 tons/acre/year. The EPA asserts sediment
runoff rates from construction sites are 10 to 20 times
greater than those from agricultural lands, and 1,000 to
2,000 times greater than those of forest lands. During a
short period of time, construction activity can
contribute more sediment to streams than is naturally
deposited over several decades, causing physical and
biological harm to our nation's waters. For more
information check out this EPA report on
Management
Measures For Urban Areas. |
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