The Relation of Trends in Fecal Coliform Concentrations in a CSO Impacted River to Their Sources

We performed a statistical and graphical analysis of fecal coliform (FC) concentration data from four sites in a combined sewer outfall (CSO) impacted stretch in the lower Passaic River in New Jersey in order to distinguish between continuous point sources and intermittent stormwater-related sources of FC. Trends and correlations were developed to identify the relationship between FC concentration and various proposed causative variables, including temperature and river discharge. These relationships facilitate the determination of a total maximum daily load (TMDL) for the river. We observed that dilution produced by variations in the stream discharge controls the FC concentration more than the fecal coliform loading rate. As a result, the additional loading produced by the storm runoff (including CSO discharge) was more than compensated for by the increased dilution. In addition, FC concentrations increased with surface water temperature, indicating warm weather sources, possibly due to wildlife. Load duration analysis was carried out to distinguish steady sources from intermittent diffuse sources. This analysis indicated the presence of steady loading in the vicinity of the combined sewer overflows (CSOs). Further analysis by the load-discharge method, in which fecal coliform loads were regressed against discharge data, indicated that the two major CSO impacted sites had steady sources only during warm weather. The data also showed that high concentrations due to the first flush effect have a very short-term presence in the river.