Combined Sewer Overflows

Much of the City’s system is a combined system, the function of which is to collect sanitary flows and stormwater runoff and convey them to the interceptor system. Combined flow in excess of the interceptor capacity is discharged to receiving waters by the regulators through CSO outlets. The City presently has 35 permitted CSOs, most of which activate during rain events. (Three additional outlets have been eliminated through separation or abandonment). These outlets discharge to Clark’s Cove, New Bedford Harbor and Buzzards Bay.

In 1994, the EPA issued a national CSO policy (the “1994 CSO Policy”) that requires communities to implement short-term best management practices often called Nine Minimum Controls (the “NMC Requirement”), as well as to develop a long-term control plan to mitigate and reduce CSOs and their effects on receiving water quality.

The Division has actively addressed CSOs since 1989. The frequency and severity of overflows has declined in the past six years as a result of the Divisions efforts to improve maintenance of the collection system and complete capital projects that have increased conveyance capacity. Although current data is not available on either the total volume of CSO discharges or the frequency of overflows, one indication supporting this contention is that the Division has been successful in reopening two large shellfishing beds that had been closed for over 30 years. Shellfishing areas are particularly sensitive to the adverse impacts of CSO discharges and reopening of the beds is indicative of the fact that these impacts have been mitigated.

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