Urban Runoff as a Public Health Concern in the Greater Milwaukee Area

Stormwater and combined sewer overflows (CSOs) are two of the major sources of water pollution in the greater Milwaukee area. In response to charges that combined sewer overflows were the primary cause of poor water quality at local beaches, the Milwaukee Metropolitan Sewerage District (MMSD) with the assistance of Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee initiated an investigation of how pollutant concentrations from combined sewer overflows compared to concentrations from stormwater. Although much historical data exists to characterize combined sewer overflows, less data is available for stormwater. Therefore, a stormwater runoff sampling program commenced in 2000 for 33 parameters at 18 monitoring sites representing a variety of land uses. The data was analyzed to identify spatial and temporal trends, seasonal variability, and the relationship between first and second flush concentrations. Total pollutant concentrations from stormwater were compared to concentrations from combined sewer overflows. This comparison showed that many pollutants in stormwater were at a higher concentration than pollutants in combined sewer overflows. Stormwater runoff events occur much more frequently than combined sewer overflows. Based on this study, stormwater, not combined sewer overflow, is the dominant source of pollutants for local waterways.