Manayunk Sewer Basin Project: Innovative Green Design

Client: Philadelphia Water Department
Location: Philadelphia, PA

As part of its long term control plan, the Philadelphia Water Department (PWD) retained Hazen and Sawyer to design a 3.75-million gallon combined sewer overflow (CSO) detention facility on Venice Island in the Manayunk section of the city – a compact site between the Schuylkill River and an active railroad and the historic Manayunk Canal and in the vicinity of parkland, a recreational facility, and business district – a sensitive area requiring careful consideration of neighborhood impacts.

Project Outcomes and Benefits

  • The CSO detention basin was constructed underground, with public parking and facilities redesigned and restored atop the basin.
  • The facility will eliminate adverse impacts on water quality that result from CSO discharges to the Schuylkill River, a source of drinking water for the City of Philadelphia.
  • The Head House that sits atop the basin is a LEED-silver eligible building with numerous energy-saving and sustainable design measures.
  • The basin is situated below a public park that includes athletic courts, scenic gardens, and a children’s spray garden.
  • The 4-plus-acre site redevelopment includes a centerpiece 250-seat, state-of-the-art performing arts center for the City of Philadelphia Parks and Recreation, replacing a deteriorating recreation facility demolished during construction.
  • The site design includes numerous best management practices (BMPs) to manage stormwater runoff, including rain gardens, green roofs on both the head house and performing arts center, rain harvesting tank, pervious pavement, and selective native and self-sustaining vegetation.

Hazen and Sawyer designed the Head House with a swooping greenroof that blends well with the surrounding area parkland. The facility contains many environmentally-friendly features and is LEED silver-eligible.

An early rendering of the Head House.

The CSO detention basin was constructed underground, with public parking and facilities redesigned and restored atop the basin.

The site features a public park that includes athletic courts, scenic gardens, and a children’s spray garden.

The site also includes a brand-new 250-seat performing arts space for City of Philadelphia Parks and Recreation use.

Both the Head House and the performing arts center feature green roofs to help manage runoff.

In its mission to protect river water quality through sustainable design which blends traditional and green infrastructure solutions, PWD with various partners, has completed the construction of an ambitious project that transforms and increases the aesthetic value of the project site on lower Venice Island along the Schuylkill River while meeting water quality goals. The site accommodates PWD’s CSO underground detention basin and the Head House situated above the basin. In addition, PWD in concert with the community, developed a plan that results in a full-scale reconstruction of the site’s parking and recreation facilities.

Hazen and Sawyer designed an innovative, LEED silver-eligible structure to house the equipment associated with the CSO detention facilities, comprised primarily of a concrete basin that receives flows by gravity when the adjacent interceptor becomes surcharged during storm events. The facility pumps flows back to the interceptor when the storm event has subsided and the interceptor has sufficient capacity to convey these flows to the sewage treatment plant. Flows are expected to be diverted to the new facility about ten times per year. Hazen and Sawyer utilized state-of-the-art InfoWorks modeling software, converting PWD’s prior (EPA-SWMM) model to analyze hydraulics and design the detention basin as well as the inlet and outlet structures.

Hazen and Sawyer’s design of the aboveground Head House incorporated the use of many “green” features, including a “living” roof system with drought-resistant sedum plantings; rain gardens through-out the site to manage storm water run-off; a glass stair tower to allow light to enter all sides of the building and reduce the need for interior lighting; photo and occupancy sensors for energy efficiency; shade and reflection devices for sun control, to reduce the need for air conditioning; and water-conserving plumbing fixtures.

For more information on this project, or to discuss a similar project in your area, contact

Mark Bottin, P.E. at mbottin@hazenandsawyer.com