Stormwater Benefits Analysis Chicopee, Massachusetts

Faced with a potential 200 million program cost to abate the impacts of combined sewer overflows, the City of Chicopee, Massachusetts (population 58,000) embarked on an innovative program to reduce the extent of the problem and create a new local source of revenue, before implementation of conventional abatement measures. The program has been extremely successful in educating the City and its consultants on the relationship between land use, soil characteristics, and stormwater runoff. It also provided the City with technical information to support the establishment of a new stormwater management fee to fund stormwater and combined sewer overflow projects.The City of Chicopee is sewered by a collection system that consists of more than 200 miles of both combined and separated sewers. During precipitation events, the capacity of the City's collection system and the wastewater treatment plant (WWTP) is often exceeded, thus resulting in up to 30 combined sewer overflows (CSOs) to the Chicopee River and Connecticut River.The City has been under an Administrative Order from the U.S. Environmental Protection Agency since 1995 to mitigate these CSO discharges. As part of the Administrative Order, the City elected to prepare a Stormwater Benefits Analysis to estimate the amount of runoff entering the combined system and evaluate means of reducing the amount in order to reduce or possibly eliminate CSOs.The City recognized that privately owned properties are a major source of stormwater runoff and reducing runoff from these sources may provide significant benefits to the combined sewer collection system. The City is considering a stormwater ordinance to encourage large commercial and industrial site owners, as well as smaller site and residential owners, to implement projects that reduce storm runoff entering the sewer system.The Stormwater Benefits Analysis was prepared to provide estimates of the existing volume of storm runoff entering the combined sewerage system. The analysis also projected an estimate of storm runoff reduction that could be obtained through implementation of a stormwater ordinance. Factors affecting runoff reduction included anticipated participation rates, existing land use and density, subsurface soil conditions, topography, and collection system conveyance and configuration.The results of the evaluation indicated that the establishment of a stormwater ordinance to encourage private-based initiatives might provide a modest reduction in runoff to the combined sewer collection system, ranging between 11% to 19% for the evaluated precipitation events. Although stormwater ordinance implementation alone is unlikely to eliminate any of the City's CSOs, it will become an integral part of the City's strategy to help preserve capacity within the collection system and the WWTP. This, in turn, will allow the City to reduce CSO volumes and frequency as part of its future Long-Term CSO Control Plan.