Sewage Contamination under Different Storm and Hydrologic Conditions in Three Urban Waterways

Abstract:

Fecal contamination in urban waterways is a major public and environmental health threat. Sanitary sewer and combined sewer overflows are major point sources of fecal pollution. Additionally, stormwater runoff and failing sewer infrastructure contribute fecal contamination and pathogens to urban waterways. Traditionally, fecal indicator bacteria such as E. coli, enterococci, and fecal coliforms are used to gauge fecal contamination in water; however, these general indicators are unable to distinguish fecal sources in the environment. This study used two human-specific fecal indicator bacteria to identify human sewage contamination in Milwaukee, Wisconsin, where three rivers form an estuary that discharges to Lake Michigan. Two-hour composite samples were collected at four sites, one in each of the three rivers and one in the estuary, to represent the entire hydrograph before, during, and after a rain event. Samples were collected throughout a variety of conditions, including dry-weather baseline, light and heavy rain events, and combined sewage overflows (CSOs). These samples were analyzed using quantitative polymerase chain reaction (qPCR) assays to determine human sewage loads in each river during each type of event. Low levels of human indicators were found during dry-weather baseline conditions, and loads increased significantly (one to two orders of magnitude) during rain events. Sampling upstream of the estuary indicated sewage contamination was originating in the heavily urbanized part of the watersheds, likely a result of failing infrastructure. CSO events contributed the highest loads, which were on average ten-fold higher than rainfall events with no CSO. This information will be a useful for directing the efforts of local agencies and municipalities to investigate failing infrastructure, as well as agencies at the state and federal levels to create appropriate goals to address the human health concerns that are posed by sewage contamination in urban waterways.