What is being done to control or eliminate CSOs in Massachusetts?

CSO discharges are regulated by MassDEP and EPA in accordance with state and federal CSO policies and the State Water Quality Standards (WQS). Massachusetts previously had 24 CSO permittees, but there has been a reduction to 19 CSO permittees that have National Pollutant Discharge Elimination System (NPDES) permits issued by EPA Region 1 and MassDEP's Surface Water Discharge Permitting Program. Communities with CSOs include most of the older urbanized communities across the state, such as Boston, New Bedford, Worcester, and Springfield.

Each CSO permittee must implement system controls known as the Nine Minimum Controls.  The purpose of these controls is to maximize the efficiency of existing facilities in order to limit the duration and impact of CSO discharges.

The Nine Minimum Controls are:

  • Proper operation and regular maintenance programs for the sewer system and CSO outfalls.
  • Maximum use of the collection system for storage.
  • Review and modification of pretreatment requirements to ensure that CSO impacts are minimized.
  • Maximization of flow to the POTW for treatment.
  • Elimination of CSOs during dry weather.
  • Control of solid and floatable materials in CSOs.
  • Pollution prevention programs to reduce containments in CSOs.
  • Public notification to ensure that the public receives adequate notification of CSO occurrences and CSO impacts.
  • Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls.

Show All Answers

1. What are Combined Sewer Overflows (CSOs)?
2. What happens in to the combined sewer during wet weather?
3. What is being done to control or eliminate CSOs in Massachusetts?
4. What happens in a combined sewer during dry weather?