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Philadelphia Water Department - SMIP

Stormwater pond retrofit for industrial corporation reduces CSOs in Philadelphia

Philadelphia Water Department - SMIP

Philadelphia, PA


Philadelphia is one of over 770 U.S. cities with combined sewer systems, the overflows from which represent a major source of water pollution. Nearly 60 percent of the City's sewers are combined, with more than 11 billion gallons of stormwater and its pollutants discharged into local waterways each year. To address this issue, Philadelphia Water Department (PWD) has implemented Green City, Clean Waters, a comprehensive plan focused on reducing stormwater pollution to the City's sewers with investments in both public green infrastructure projects and private partnerships. PWD, along with the Philadelphia Industrial Development Corporation (PIDC), incentivizes private property owners to implement stormwater management solutions through the Stormwater Management Incentives Program (SMIP). 

A commercial property in the City of Philadelphia was redeveloped in 2007. At that time, 206,701 square feet of impervious area of runoff were routed through an on-site retention basin. However, the basin did not meet current PWD Stormwater Management Regulations and operations challenges had prevented the site from earning stormwater credits towards the Stormwater Management Service Charge (SMSC). The commercial landowner engaged Opti in November 2016 to improve the performance and function of the basin as well as create a long-term operations and maintenance plan for the entire property. A SMIP grant was awarded to fund the retrofit of the basin to increase treatment and reduce wet weather flows.

For more information on this project, please see this case study.


Since implementation in November 2016, the site experienced 5 million gallons of inflow from 69 different rainfall events over the course of one year. The CMAC-enabled system prevented 4.9 million gallons of wet weather flow or 98% of total flow into the City’s combined sewer. By comparison, a passive site (i.e. without CMAC) would have only prevented 36% wet weather flow during the same analysis period.

Fast Facts
  • System Start Date

    November 2016

  • Objectives

    CSO Mitigation

  • Application

    Stormwater Pond

  • Products Used


  • Project Partners

    Amec Foster Wheeler; PEER Environmental, LLC

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