The Philadelphia, Pennsylvania metro area covers nearly 150 square miles and is home to more than 1,500,000 people. Its urban landscape of buildings and roadways—including miles of paved surfaces—makes managing stormwater a challenge. As a result, stormwater runoff and frequent combined-sewer overflows were affecting the city’s water quality.
Traditionally, cities with combined sewers have collected and treated stormwater to prevent flooding and pollution, eventually returning it to a waterway. But storing stormwater requires large, expensive storage systems that require pumping each time it rains. Instead, the Philadelphia Water Department sought a more affordable, environmentally friendly way to both manage its stormwater and comply with Clean Water Act regulations.
CDM Smith worked with the Philadelphia Water Department (PWD) to develop a plan that would green almost half of the combined sewer portion of the city, creating a patchwork of natural spaces that would manage stormwater by replicating the natural water cycle. This green infrastructure, primarily infiltration systems with vegetation and soil, helps soak up and store excess water.