10 Years of Green Stormwater Infrastructure: Receiving Water Modeling for Philadelphia’s Green City, Clean Waters Combined Sewer Overflow Control Program at Year 10 of Implementation

Philadelphia Water Department (PWD) has recently prepared a report documenting the progress of the Green City, Clean Waters Combined Sewer Overflow (CSO) Long-Term Control Program from its inception in 2011 through 2021 (Year 10 of program implementation). This Evaluation and Adaptation Plan (EAP) report was submitted as a requirement of the City’s Consent Order and Agreement with the Pennsylvania Department of Environmental Protection. Water quality and hydrodynamic models of the tidal Delaware River and nontidal tributary creeks were developed and utilized to simulate water quality conditions within these CSO receiving waters using US EPA’s Environmental Fluid Dynamics Code (EFDC) at Year 10 of the program. To simulate the impact of CSO controls on the receiving waters, a model framework was established that focused on the contribution of CSO to water quality criteria exceedances in the receiving waters. This framework was applied to models developed during an extensive model validation effort for fecal coliform bacteria and dissolved oxygen. Additionally, considerations such as sea level rise and other water quality and hydrologic assumptions were applied. This presentation will summarize the status of CSO control implementation, including green infrastructure and other infrastructure projects, resulting estimated CSO volume reductions, and how these controls were represented in the Year 10 scenarios. Water quality model development, the tools developed to compare model results against applicable water quality criteria, and an overview of the analysis of the model results included in the Year 10 EAP Report will also be highlighted.