The Integration of Receiving Water Impacts in the Evaluation Process of Alternative Designs for CSO Abatement in Providence, RI

The Providence, Rhode Island sewer system is undergoing a combined sewer overflow abatement program. One measure of the program's effectiveness is the reduction of water quality impacts to portions of the Providence River and upper Narragansett Bay. A series of models, both land-based and receiving water-based, were used in the evaluation of design alternatives. SWMM was the land-based model and WQMAP was the receiving water-based model used. Model analyses were performed on a series of 13 design alternatives. Comparative measures used included the reduction in overflow volume, reduction in overflow events, reduction in the receiving water area impacted and its duration, and reduction in the fecal coliform loading. The preferred alternative consisted of a combination of near surface storage facilities and deep tunnel storage.