Modeling CSO Impacts from Nashville Using EPA's Demonstration Approach

Abstract

Consoer Townsend Envirodyne (CTE) Engineers and Vanderbilt University's department of civil and environmental engineering are involved in a four-year study to mathematically model the water quality of Cheatham Lake on the Cumberland River below Nashville and to determine the influence of Combined Sewer Overflow (CSO) discharges. The state of Tennessee requested that Metropolitan Nashville Department of Water and Sewer Services (Metro) demonstrate whether their CSO discharges were causes of severe dissolved-oxygen deficits found in the reservoir from time to time. The water-quality model that was used, CE-QUAL-W2, has been calibrated and verified with 36 months of data, including 12 months of intensive monitoring and continuous data collection. Modeling results showed few of the predicted dissolved-oxygen values deviating more than 1.0 mg/L from measured values. Model predicitons showed that even under low-flow conditions, CSO discharges had little impact on the dissolved oxygen of the lake. The model has been used to make projections of results likely to be achieved by various CSO control scenarios.