Section 402(P) of the Water Quality Control Act of 1987 requires that municipalities with a population of 100,000 or more obtain permits to discharge stormwater runoff and to control its quality. Monitoring and sampling of stormwater runoff from seven drainage basins in Madison, Wis., was performed from April 1993 through November 1994 by the U.S. Geological Survey and the city of Madison to (1) characterize the quantity and quality of wet-weather discharge, (2) determine storm and annual loadings of selected constituents, and (3) characterize rainfall and runoff conditions. The seven basins were selected for monitoring rainfall and runoff on the basis of land-use characteristics, dry-weather flow conditions, and monitorability.
As required by Section 402(P) of the Water Quality Control Act of 1987, stormwater-runoff samples collected during storms that met three criteria (rainfall depths 50 to 150 percent of average depth range, rainfall durations 50 to 150 percent of average duration, and antecedent dry-weather period of at least 72 hours) were analyzed for semivolatile organic chemicals, total metals, pesticides, polychlorinated biphenyls, inorganic constituents, bacteria, oil and grease, pH, and water temperature. Two of the seven sites also had samples analyzed for volatile organic chemicals. In addition to the required sampling, additional runoff samples that did not necessarily meet the three rainfall criteria, were analyzed for total metals and inorganic constituents. Storm loads of selected constituents were computed.
