LTCP and the USEPA CSO Policy

The United States Environmental Protection Agency (USEPA) issued a national CSO Control Policy in 1994, requiring communities with combined sewer systems to develop Long Term Control Plans (LTCPs) that will provide for compliance with the requirements of the Clean Water Act, including attainment of current or revised water quality standards.

USEPA’s CSO Control Policy

The major objectives of the 1994 CSO Control Policy are to:

  • Prohibit dry weather overflows
  • Bring all wet weather CSO discharges into compliance with the technology-based and water quality-based requirements of the Clean Water Act
  • Minimize water quality, aquatic biota and human health impacts from CSOs

The 1994 USEPA CSO Control Policy mandates that all municipalities that have CSSs with CSOs should undertake a process to:

  • Accurately characterize their sewer systems
  • Demonstrate implementation of the NMCs
  • Develop a CSO LTCP


The CSO Control Policy also requires permittees to implement the Nine Minimum Controls (NMCs), which are operations and maintenance measures that can reduce the prevalence and impacts of CSOs and that are not expected to require significant engineering studies or major construction.  The NMCs are:

  1. Proper operation and regular maintenance programs for the sewer system and the CSOs
  2. Maximum use of the collection system for storage
  3. Review and modification of pretreatment requirements to assure CSO impacts are minimized
  4. Maximization of flow to the publicly owned treatment works for treatment
  5. Prohibition of CSOs during dry weather
  6. Control of solid and floatable materials in CSOs
  7. Pollution prevention
  8. Public notification to ensure that the public receives adequate notification of CSO occurrences and CSO impacts
  9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls

USEPA’s Guidance for NMCs:

As per the USEPA CSO Control Policy, an LTCP must address:

  • Characterization, monitoring, and modeling of the CSS through collecting rainfall records, CSO and flow data, and modeling of the CSS
  • Public participation
  • Consideration of sensitive areas
  • Evaluation of alternatives
  • Cost and performance considerations
  • Operational plan
  • Maximizing treatment at the existing treatment facility
  • Implementation schedule
  • Post-construction compliance monitoring program


The LTCP can also include demonstration of the NMC implementation.

The BSA’s State Pollutant Discharge Elimination System (SPDES) permit requires that the BSA develop a CSO abatement facility plan in accordance with the USEPA CSO Control Policy.  Furthermore, the SPDES permit requires the BSA to implement the Best Management Practices (BMPs) for CSOs and to develop a CSO Abatement Plan.  The BMPs are equivalent to the Nine Minimum Controls (NMCs) required under the USEPA CSO Control Policy.  The CSO Abatement Plan must satisfy the requirements for a LTCP as identified in the USEPA CSO Control Policy and must be completed in accordance with New York State Department of Environmental Conservation (NYSDEC) requirements.

NYSDEC’s website:

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