Many streams in or near urban areas are polluted; some carry significant amounts of pollution when there is no obvious source. Intensified studies of runoff of storm water in urban areas that are n ow under way as part of a joint effort by the U.S. Geological Survey, Department of the Interior, and the Environmental Protection Agency appear to have isolated the origin. There are pilot studies in Philadelphia, Denver, Portland, and the Miami and south Florida area that have produced reliable data for the first time, according to the descriptions given by D.J. Lystrom (hydrologist and coordinator of the USGS programs) at a recent meeting on urban storm water management in Raleigh, North Carolina.
Instead of point sources such as industrial concerns and municipal waste treatment plants, many of which have been cleaned up greatly in the areas studied, less obvious sources such as storm water runoff from streets, parking lots, and agricultural land have been identified. Lystrom said that the study in Portland, for example, showed that storm water runoff may have supplied higher concentrations of ‘settable solids and coliform bacteria’ than the discharge from secondary waste treatment plants. The study in Denver indicated that storm runoff may contribute significant amounts of ammonia nitrogen, total nonfilterable residue, copper, iron, lead, and zinc, and in winter, sodium chloride and steel deicing chemicals to local streams.