Reducing nonpoint source pollution in ultra-urban areas: Two case examples

Many municipalities are challenged with requirements to reduce nonpoint source pollution from intensively developed areas with little or no space for conventional best management practices (BMP's). These areas often include commercial and/or industrial land use; and these land uses are typically identified as significant sources of urban nonpoint pollution. Within the 16.2 ha (40 acre) festival grounds (Henry Maier Park) in downtown Milwaukee Wisconsin, the creation of a small landscaped island provided an opportunity for managing nonpoint source pollution. A flow splitter diverted the first flush stormwater from a 1.2 ha (3.0 acre) area to a constructed landscaped island. The landscaped area was graded as a depression and lined with a layer of peat over a layer of fine graded sand. Under lying the sand perforated collection pipes intercepted the filtered stormwater and returned the water to the storm sewer system. At St. Mary's Hospital in Green Bay, WI a pressurized, two stage filter system was designed to reduce pollution from a 2.6 ha (6.5 ac) parking lot. The system proved more economical, treated a greater amount of runoff, and also removed a greater percentage of annual pollution than gravity driven sand filtration systems.