COMBINED SEWER SYSTEM

COMBINED SEWER SYSTEM

The Borough of Ashland has a “Combined Sewer System” (CSS). A combined sewer system is a sewage collection system of pipes and tunnels designed to also collect surface runoff. The tunnels were built to convey water from the mines and surface runoff from the Borough to the Mahanoy Creek. As the Borough grew, sanitary sewage was added to the system. This type of system was typically built in the early 1900s. As part of the design, regulators were built into the collection system as relief points during high wet weather flows. The system conveys all normal dry weather sewage flows to the treatment plant where it is treated and discharged as clean water to the Mahanoy Creek.


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What is a CSO?

A Combined Sewer Overflow (CSO) is a designated discharge point or regulator for release of the combined wastewater when the capacity of the CSS is exceeded during wet weather. CSOs can occur during heavy rain or sudden snow melt that causes the capacity of the combined sewers to be exceeded. When this occurs, sanitary sewage can mix with runoff from buildings, streets and parking lots and flow untreated into the local receiving waters. At the time that they were designed, CSOs were constructed to prevent overloading of the sewer system and also prevent basement and street flooding. In the State of Pennsylvania, there are 137 communities with 1,642 discharge points that are part of combined sewer systems.

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: http://www.epa.gov/sites/production/files/2015-10/documents/owm0111.pdf

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
  • Miminimize 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 impacts of CSOs and that are not expected to require significant engineering studies or major construction.  The NMCs are:

  1. Proper operation and maintenance programs for sewer systems and 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 efficiency of CSO controls.

USEPA’s Guidance for NMSs:  http://www.epa.gov/npdes/pubs/owm0030.pdf

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

Public Participation

A key component in the development of the system-wide LTCP is public participation, or community outreach.  The purpose of public participation is to increase awareness and inform the community about its Long Term Control Plan for CSOs.  The Borough of Ashland could develop a community outreach program that included the following components:

  • Stakeholder Panel
  • Focus Groups
  • General Public