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Traditional Infrastructure Tools

The Philadelphia Water Department oversees a large magnitude of traditional infrastructure, including approximately 3,000 miles of sewer piping, 79,000 stormwater inlets, 3 drinking water treatment plants, 3 sewage treatment plants, more than 25 pump stations, 175 CSO regulating chambers, 164 CSO outfalls, and more than 450 stormwater outfalls.

Southwest Water Pollution Control Plant, Philadelphia, PA


A subsurface network of pipes totaling approximately 3,000 miles in length convey stormwater, wastewater, and sewage. The pipe network, comprised of sanitary, combined and storm sewers, ranges in diameters from 8 inches to 22 feet. These sewers are constructed of brick, concrete, terracotta, or vitrified clay that are egg, circular, V-bottom, arch, ellipse, or irregular in shape.

Sewer Relining

Sewer Relining is the maintenance and repair of the sewer system. It involves repairing the lining of the sewer walls in order to reinforce, seal and rehabilitate them. Once inflow and infiltration locations have been identified, excessively leaky pipes can be repaired, allowing the full pipe capacity to be reserved for sanitary and storm flow.


Off-line storage aims to reduce flooding in urban areas and reduce adverse effects of flushing raw sewage into receiving waters by diverting flow into temporary holding reservoirs and tank chambers. Off-line storage can refer to underground influent channels, retention tanks, consolidation conduits or satellite storage for remotely located outfalls.

In System Storage

In System Storage is the concept of modifying existing infrastructure to more effectively store volumes of water during wet weather events. PWD infrastructure is typically designed for a five-year event, and as such is oversized for the majority of events that occur in the typical weather patterns of Philadelphia. This excess storage volume can be used more effectively to not only convey, but to store stormwater from smaller wet weather events.

Treatment Plants

Stormwater runoff, wastewater and household sewage are directed to treatment plants where they undergo a process of removing physical, chemical and biological contaminants. The objective is to produce treated effluent and solid waste that is suitable for discharge or reuse back into the environment.

Satellite Treatment

Located in the area surrounding main treatment plants, satellite treatment facilities are one method of managing peak combined sewer flows and preventing flooding and downstream erosion. Acting similarly to a retention basin, satellite plants supplement main treatment plants by storing part of the wastewater volume. If capacity is exceeded during a storm, these emergency overflow structures maintain the flow in the combined sewer system rather than discharging into receiving waterways. The wastewaters – typically treated for nutrient and solids removal – are gradually returned to the sewer system during dry weather periods, so all flow volumes can ultimately pass to wastewater treatment plants when capacity is available.