Development Of Methods To Define Water Quality Effects Of Urban Runoff

Abstract

The projected costs for treating CSO and urban runoff nationwide are extremely large, and therefore necessitates that methods be available to quantitatively evaluate the receiving water impacts associated with these discharges. This progress report summarizes the results of the first year's effort on investigating methods which can be employed to develop wet weather standards. The wet weather criteria could ultimately be employed to develop measures of benefits to be obtained from treatment of CSO and urban runoff. This project considers short-term water quality impacts that occur during or shortly after a storm event. Examples of the short term impacts are dissolved oxygen depressions due to rapid oxidation of contaminants or the death of fish as a result of short term increases in the concentration of a toxic in the receiving water. The phenomenon which characterize these impacts are related to event characteristics such as the volume and duration of the runoff, the concentration of a contaminant in the runoff, and the dilution available in the receiving water during the runoff event. This dilution can be characterized, on the scale of the total river width, by the joint occurrence of storm discharges from urban areas and the stream flow in the receiving waters. A second area of investigation in the project addresses methods for defining the effects of time variable concentrations on organism morality and includes considerations of carryover effects between storms as a result of varying instream contaminant oncentrations during dry weather.