Abstract

In the early 1990s, the U.S. Environmental Protection Agency and the New Hampshire Department of Environmental Protection negotiated a consent agreement with the City of Nashua, New Hampshire (population 100,000) to address the problem of combined sewer overflows (CSOs). In 1992 a Phase I CSO study was completed as a first step towards the long-term abatement of these CSOs. A SWMM model of the Nashua combined sewer system was developed in 1996 as a tool to simulate alternatives for CSO control, which included treatment and storage facilities. This chapter describes the development of the model's input, its calibration, and its use for long-term continuous simulations. This model utilized a broad range of SWMM features, including RUNOFF, TRANSPORT, EXTRAN, TEMP, RAIN, and STATISTICS blocks. It demonstrates the feasibility of long-term continuous simulations for urban sewer systems, while also highlighting present limitations of the SWMM model that must be addressed before continuous EXTRAN simulations are practical for larger cities.

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