The Interstate 95 Girard Avenue Interchange (GIR) area is one of the most heavily traveled interstates in Pennsylvania, carrying more than 185,000 vehicles per day. When the road was re-constructed, storm water management was a priority to ease strain on the city’s CSS and create green space in an urban environment.
“Prior to the reconstruction of I-95, there were no existing storm water management practice facilities to control or treat the roadway runoff,” said Edwina Lam, water resources task lead with AECOM. “All highway runoff was discharged to the Philadelphia Water Department’s combined sewer system, which during a rain event caused the system to overflow and discharge directly to the Delaware River.”
The project began with Section GR2, the smallest section at approximately 1,200 ft in length, where 10 narrow bioswales were created. While the bioswales positively impacted the area, the Pennsylvania Department of Transportation (PennDOT) sought answers to storm water design challenges and long-term performance questions. This led to the University Monitoring Program, a partnership that launched in 2016 with Villanova and Temple universities to help monitor and optimize the interstate’s storm water management designs.
“From the research and lessons learned in Section GR2, Villanova and Temple universities have already influenced the future designs throughout I-95 corridor within the city of Philadelphia,” Lam said. “The development of the storm water management sites and design has been an extensive process, but we are proud of the outcome and impact it will have.”
The research revealed that while the storm water management practices were effectively managing flow and improving water quality, the bioswales were subject to erosion due to high flow rates. This led the project to adapt and design a treatment train system, comprised of three smaller rain gardens connected by vegetative swales with check dams. All gardens in later sections GR3 and FR4 have brick paver forebays as a low maintenance facility for sediment removal.
Creating green space in an urban environment has proved challenging at times. One unique challenge the project faced was variable soils and infiltration rates. When the interstate was originally constructed in the 1960’s, houses demolished to create room for the highway were broken into smaller pieces and used as fill material. Additionally, the city’s old age meant some utilities were unaccounted for on existing plans. The old age also contributed to archaeological artifacts being discovered, with some larger pieces even incorporated into site design.
“Prior to the reconstruction, there was limited green space and any pervious areas owned by PennDOT were fenced in and not accessible,” Lam said. “After the reconstruction, green spaces were created with planted areas that are open to the community to enjoy ... Most importantly, the storm water sites are managing the water from the highway, which reduce local flooding and help keep local waterways clean.”