Spatial and temporal variations of indicator bacteria densities in the receiving waters of combined sewer overflows: The Allegheny River in Pittsburgh, Pennsylvania.

摘要

This exploratory research investigates trends in Escherichia coli densities in the Allegheny River in Pittsburgh. Bacteria densities were monitored following combined sewer overflows during summer 2011. Using the Colilert-18 E. coli enumeration method, this research contributes to the understanding of contamination characteristics in an urban river as related to spatial and temporal E. coli trends. Sampling was successfully accomplished by conducting a five-point cross-channel transect every 12 hours for 72 hours following precipitation events. Results indicated that contamination resulting from heavy precipitation resulted in water quality impairment for up to 72 hours and E. coli densities greater than one order of magnitude above published health criteria. Light precipitation events resulted in impairment for only 24 hours with E. coli densities marginally above health standards. In both instances, contamination peaked at 12 hours after the end of precipitation. Bacteria concentrations did not decrease linearly - fluctuation occurred for several days following overflows likely caused by upstream contamination and sediment resuspension.