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STORMWATER
MS4 Permittees
MS4s are Municipal Separate Storm Sewer Systems, collection systems designed to
transport rainwater or melted snow through a series of storm drains, pipes,
ditches and open channels straight to our streams and rivers. The water that
flows into the storm sewer system is called stormwater runoff. Before entering
the system, it picks up pollutants as it travels across yards, streets, parking
lots and pavement. In a separate storm sewer system, stormwater runoff is not
treated; therefore, all of the pollutants it carries flow directly into our
waterways.
All MS4 operators throughout the United States are required to obtain a
National Pollutant Discharge Elimination System (NPDES) permit in order
to discharge stormwater runoff into the waterways. These permits require MS4
operators to develop, implement and enforce a comprehensive stormwater
management program to reduce the discharge of pollutants, educate the public
about stormwater and protect water quality in their watersheds. There may be
multiple watersheds within a municipality and multiple municipalities within a
watershed.
A watershed consists of all the land that “sheds” or drains stormwater down to
the same body of water, such as a creek or stream. Hundreds of watersheds exist
throughout southwestern Pennsylvania. The smaller watersheds (creeks and
streams) drain to one of Pittsburgh’s four rivers (Allegheny, Ohio, Monongahela
and Youghiogheny) and ultimately to the Ohio River Basin. The Ohio River Basin
drains to the Mississippi River, which leads to the Gulf of Mexico.
The important thing to remember about watersheds is that what we do on land
affects water quality for our neighboring communities downstream.
To see a list of all southwestern Pennsylvania MS4 permittees
by municipality and the watersheds to which they flow,
click here.
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