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Storm Water Regulation

Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events. This runoff often contains pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by a National Pollutant Discharge Elimination System (NPDES) permit under the federal Clean Water Act. The primary method to control storm water discharges is through the use of best management practices (BMPs).

As storm water enters a conduit or pipe, it is classified as a point source and becomes subject to regulations concerning its discharge. All point source discharges are subject to water quality standards. Section 303(d) of the Clean Water Act (CWA) requires “states to submit lists of surface waters that do not meet applicable water quality standards (impaired waters) after implementation of technology-based effluent limitations, and establish TMDLs (total daily maximum loads) for these waters on a prioritized schedule.”

A TMDL specifies the maximum amount of a pollutant that a body of water can receive and still meet water quality standards, and allocates pollutant loadings among point and nonpoint pollutant sources. By law, EPA must approve or disapprove lists and TMDLs established by states, territories, and authorized tribes. All watersheds with TMDLs are subject to storm water discharge limits for the pollutant(s) of concern.

Water Quality Standard- Each state classifies its bodies of water according to that body’s specific uses. States determine the criteria for classes of use based on historical data, social factors, and economic influences. The state then tests the water body to determine whether it meets the criteria for its class. If it does not meet all of the criteria for the class it is listed as a non-attainment water. All waters designated as non-attainment by their state are subject to a TMDL. Tests are then carried out to decide the pollutant load that the the water body could carry on a daily basis while still being able to meet its designated use criteria.

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