Abstract

A floatables trap was installed at the mouth of a combined sewer outfall in the Buffalo River, NY, to evaluate the utility of this technology in reducing floatables dispersal. In addition to the floatables trap, two Hydrolab Datasondes were installed to demonstrate the importance of a continuous monitoring system in evaluating impacts of combined sewer overflows (CSOs) on receiving water body quality. One Hydrolab was hung in the river from the floatables trap near the mouth of the outfall and one was attached to an upstream bridge abutment, to represent ambient river conditions. Monitored parameters included dissolved oxygen, pH, conductivity, temperature, and redox.

Floatables were collected successfully over an eight week period that included both dry weather and three CSO events. The dry weather floatables were collected and analyzed as representative of fugitive inputs from the river that were not related to CSO activity. The floatables were sorted into nine categories and the number, mass, and volume in each category were determined. Mean floatables accumulation rates in the trap were significantly greater for CSO periods than dry weather periods. The distribution of floatables, by category, in the sampled CSOs was compared to the distribution for two sewersheds from a study conducted in Newark, New Jersey. The distributions for the two New Jersey sewersheds were similar to each other, but the floatables in Buffalo consisted of more wood and less plastic. The average mass of floatables trapped per 1,000 cubic feet (28.3 m3) of CSO discharge was considerably less for the Buffalo sewershed than the averages for the two New Jersey sewersheds. Low floatables discharge from the Buffalo sewershed, in part, may be due to sewer hoods.

In general, the results for parameters measured with the Hydrolabs were similar to past spot sampling done on the river. Of greatest interest were the results for dissolved oxygen. Classically described dissolved oxygen sags were not observed in the river at the mouth of the outfall during CSO events. In fact, the greatest decreases in dissolved oxygen levels (at both sites) were observed in association with navigational dredging activities, likely due to sediment oxygen demand when sediment was resuspended.

This paper is only available in PDF Format:

  View full text PDF