Green Stormwater Infrastructure Design: Lessons Learned in Philadelphia

In 2011, the Philadelphia Water Department (PWD) embarked on a 25-year plan to improve water quality in local rivers and streams, primarily through reduction in combined sewer overflows. This $2.4 Billion program, known as “Green City, Clean Waters”, highlights Green Stormwater Infrastructure (GSI) as the primary solution with a plan to develop 9,564 “Green Acres” in an effort to significantly reduce the annual Combined Sewer Overflow (CSO) volume. PWD has also completed a Triple-Bottom-Line analysis in order to understand the social and economic benefits that go beyond water quality improvement.Green Streets is the most prominent of the multiple Green Stormwater Infrastructure (GSI) programs that are in progress by PWD. This paper discusses the development process for Green Streets Contracts in Philadelphia as well as the formation of the program including site evaluation and selection, standardization of design details and specifications, and plans for maintenance and monitoring. It will also discuss the variables and constraints that go into stormwater system design for projects in city streets and public property. The overall goals of the Long Term Control Plan and the lessons learned in the initial phase of the GSI program are discussed including site selection, differences in tested versus actual infiltration, and utility coordination.Case studies are examined to explain GSI tools that can be used and the variables and constraints that factor into selection of these technologies are discussed. Integration of GSI projects with other infrastructure projects such as water main relay projects and sewer reconstruction projects with case studies and the various benefits of these types of projects are presented. In addition, the provisions that have been incorporated for evaluation and monitoring of system performance are reviewed as well as future initiatives that are underway at PWD.