IMPACT OF CSO AND STORMWATER RUNOFF ON WATER QUALITY IN URBAN STREAMS

Combined sewer systems (CSSs) impact water quality of receiving water bodies, especially during high discharge events, in many urban systems. Such urban systems not only receive contaminant loading from stormwater, but also as a result of sewage contributions from combined sewer overflows (CSOs). A wide range of contaminants have been detected including nitrogen, phosphorous, trace metals, coliforms and anthropogenic organics. However, the chemical composition of stormwater and CSOs varies within an event, representing contributions from multiple sources. Management of contaminant loading often ignores these temporal shifts in speciation as well as fate within the receiving water body, further compounding the difficult and challenging problem that many municipalities face of assessing ecological impacts. To assess potential changes in loading and chemical speciation we have collected stream water samples in the Park River sewershed (Hartford, CT) during base flow and events to assess potential for contaminant loading and mobilization. Three events have been collected to date. Trace metal, TSS and DOC concentrations increased with discharge. However, trace metal concentrations and flux values reflected the degree of urbanization and industry present in the watersheds. All samples contained low DOC with the majority of the flux occurring in the particulate phase. Dissolved transport with DOC, particularly for Hg, decreased with urbanization. The degree of urbanization also increased TN flux as well as the distribution among N chemical species, with urbanized systems increasing in the NOx fraction.