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Combined Sewer Overflow Program


Combined sewer systems (CSS) are wastewater collection systems designed to convey sanitary sewage and storm water (surface drainage from rainfall or snowmelt) in a single pipe to a treatment facility. In periods of rainfall or snowmelt, total wastewater flows can exceed the capacity of the CSS and/or the treatment facility. When this occurs, the CSS is designed to overflow directly to surface water bodies, such as lakes, rivers, and streams. These combined sewer overflows (CSO's) can be a major source of pollution in communities served by CSS's.

It is difficult to quantify CSO impacts on receiving water quality and the site-specific variability in the volume, frequency, and characteristics of CSO's. The financial costs of correcting CSO effects can also adversely impact a community. In order to aid the states and communities, a CSO Control Policy was published in the Federal Register on April 19, 1994. The policy is to:

  • Provide guidance to permittees with CSO's, NPDES permitting and enforcement authorities, and State water quality standards (WQS) authorities.

  • Ensure coordination among the appropriate parties in planning, selecting, designing, and implementing CSO management practices and controls to meet the requirements of the Clean Water Act.

  • Ensure public involvement during the decision-making process.

A key element of the CSO Policy is the permittees' implementation of the NINE MINIMUM CONTROLS (NMC), which are technology-based actions or measures designed to reduce CSO's and their effects on receiving water quality.  Please refer to POLICIES AND RESOLUTIONS for a detailed list of the NINE MINIMUM CONTROLS.

WWMA Requirements

Manor Borough and North Irwin Borough are the two areas in the WWMA system that maintain combined sewers. There are three CSO structures on the system at the points of connection to the WWMA interceptor sewers. One CSO structure is located in Irwin and two structures are located in Manor. Monitoring of the overflow points in each structure has been ongoing since October 1998.   

The WWMA's new NPDES permit became effective on August 1, 1998. Part C of the permit requires that the Authority submit a report to the PaDEP by August 1, 2000.  This report must provide documentation demonstrating implementation and compliance with the NMC's required on a system-wide basis. Additionally, this report must include schedules for completing minor construction activities associated with implementing the NMC's.

The NINE MINIMUM CONTROLS are listed under POLICIES AND PROCEDURES and, as you select each one, will briefly describe the type of documentation that must be provided to comply with the requirements of the NPDES permit.   



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Last modified: July 8, 2021