Like many older cities, Philadelphia relies on a combined sewer system to handle much of its stormwater. Combined sewer systems convey both wastewater from bathroom and kitchen drains and rainwater from roof drains and street inlets to sewer treatment plants that filter and purify the water before discharging to rivers and streams. In dry weather, the system works however small amounts of rain can overwhelm the system, allowing rainwater laced with road oil and litter in addition to bathroom and kitchen wastewater to overwhelm the system and gush, untreated, directly into Philadelphia’s streams and rivers causing bacteria levels to skyrocket.
In 2009, Philadelphia unveiled its 3,369-page plan to transform the city’s approach to drainage over the next 20 years. The plan relies on relatively low-tech green infrastructure measures such as rain gardens, green roofs, thousands of new trees, and porous paving to manage the billions of gallons of rainwater that overwhelm the city sewer system when it rains.
South Philadelphia’s Herron Park, designed by Langan Engineering and Environmental Services in 2008, incorporated many of the sustainable urban drainage measures cited in the city’s proposed stormwater plan. Langan provided landscape architecture, civil engineering, surveying and permitting services for restoration of the park for Philadelphia’s Department of Public Properties, which renovated the park on behalf of the city’s recreation department.