Assessing Continuous Contamination Discharge from a Combined Sewer Outfall (CSO) into a Tidal Wetland Creek: Bacteriological and Heavy Metals Indicators

Continuous discharge from a combined sewer overflow (CSO) into a tidal wetland creek in the New York City urban area was analyzed to assess the extent of water quality degradation during both dry and wet weather. A combination of fecal indicator bacteria (FIB), total suspended solids, and dissolved metals were used to infer the presence of sewage and fecal pollution from the CSO discharge and to constrain the spatial and temporal impact on water quality and dry season creek flows. Upstream of the CSO, creek flow was dominated by groundwater input, and FIB levels were very low or undetected, indicating the absence of contamination. Low-volume loading was detected in dry weather, in contrast to the expected impact when a CSO is operating as designed (flowing only following wet weather). In wet weather, a “first flush” peak was detected for some contaminants, followed by diluted contaminant concentrations due to increased flow volume but resulting in greater total loading that affected a larger area. The correlation of bacteriological and metal indicators in paired spatial and temporal samples revealed a positive relationship between the concentration of some metals (e.g. Na, Fe) and FIB. * Corresponding author: Phone 718-997-3327; Fax 718997-3299; e-mail ([email protected]) Variable patterns of peak metal concentration in the creek, with respect to precipitation and FIB level, also suggest changes in contaminant source and the influence of tidal backwater.