Large-Scale Green Stormwater Infrastructure Implementation in Philadelphia

Green infrastructure and source control technologies are increasingly accepted as a best practice for reducing stormwater impacts on water quality and aquatic habitat in urban areas. However, impacts continue to grow in many watersheds within the United States even as progress is being made on other sources of water pollution (NRC, 2009). Stormwater management practices have been improved at the site level, but they are not being implemented on a large enough scale to offset water quality degradation caused by urban and suburban land use trends (WEF Stormwater Institute, 2015). Philadelphia is one city implementing green infrastructure on a large scale as a key component of its approach to manage urban stormwater and combined sewer overflows. The Philadelphia Water Department will complete its tenth year of program implementation in 2021. This paper will cover the status of the program, provide statistics on the types and locations of green infrastructure that have been implemented, and summarize performance monitoring data collected from systems operating in the field. PWD submitted its Combined Sewer Overflow Long Term Control Plan Update in 2009, as required by its National Pollutant Discharge Elimination System permits. In 2011, a modified version of that plan was approved for implementation through a Consent Order and Agreement (COA) with the Pennsylvania Department of Environmental Protection. The COA specifies combined sewer overflow reductions, pollutant load reductions, and implementation of green stormwater infrastructure targets intended to improve water quality in local watersheds and the Delaware tidal estuary. As the program approaches the ten-year milestone, it has implemented stormwater management features managing surface runoff generated by approximately 1,100 acres of impervious urban surfaces (Figure 1). Stormwater management features have been implemented through a variety of programs and on a variety of land uses (Figure 2). These include projects on private property initiated by code requirements governing redevelopment. Projects have been implemented on public property, including streets, sidewalks, and public facilities. Finally, projects have been implemented through incentives for private property. Post-construction monitoring data from selected sites indicate that systems are generally meeting or exceeding design performance expectations (Figure 3).