Paerdegat Basin Combined Sewer Overflow Improvements

Client: New York City Department of Environmental Protection
Location: Brooklyn, NY

CSO discharges are the major source of pollution entering Paerdegat Basin. These discharges cause significant violations to state water quality standards for dissolved oxygen, coliforms, floatables, and settleable solids. Hazen and Sawyer developed a Combined Sewer Overflow facilities plan, led the preliminary and final design effort, and provided construction management services for the Paerdegat Basin CSO facilities, which serves a tributary population of 500,000 and receives CSO from a drainage area of approximately 6,000 acres.

Project Outcomes and Benefits

  • According to the our model projections, implementation of this improvement program will result in up to 70 percent reduction in Biochemical Oxygen Demand and up to 80 percent Total Suspended Solids (TSS). This, in turn, will result in very significant improvements to Paerdegat Basin and its environs.
  • The project removes the CSO sediment mound at the head of the Basin that lowered dissolved oxygen levels to near zero and caused nuisance odors in the surrounding community.
  • The design maximizes the use of existing facilities, thereby reducing costs and time.
  • Included in the project is the construction of a natural area park in the undeveloped property surrounding the basin.

CSO discharges cause significant violations to state water quality standards for dissolved oxygen, coliforms, floatables, and settleable solids in Paerdegat Basin.

Alternative construction methods for foundation excavation and dewatering were evaluated and a test-pumping program was conducted to identify designs that minimize the lowering of groundwater levels and impact on the area due to dewatering operations.

The upgraded facility will result in up to 70 percent reduction in Biochemical Oxygen Demand and up to 80 percent Total Suspended Solids (TSS), significantly improving the water quality in the Basin.

The Collection Facility South (CFS) Building's original, striking appearance - featuring the curved roof and low-lying design - was inspired by Canarsie Indian longhouses, providing the community with a gratifying visual reminder of its heritage.

The decorative tile scheme found in the lobby of the CFS Building was meticulously designed to resemble Canarsie Indian textiles – a distinctive touch ensuring that the structure's interior reflects Canarsie, Brooklyn's rich history as faithfully as its exterior.

A close-up view of the green roof designed to cover on-site CSO tanks showcases the remarkable productivity. In addition to being an aesthetically pleasant addition to the site, the green roof contributes an important sustainable element by supporting plant growth and diversity.

A key component of the CFS Building, a six-bay light maintenance garage, allows NYCDEP collection facilities personnel to efficiently and cost-effectively perform routine vehicle and equipment maintenance. The 13,000-sq.ft. garage was designed to service, at minimum, twelve crew vehicles.

Displayed proudly at the CFS Building, these flags were raised on June 6, 2008 to commemorate turning the CFS Building over to NYCDEP. This event marked an important moment for NYCDEP collection facilities personnel who previously worked in a temporary Butler building at the Paerdegat Pump Station. For them, and for NYCDEP as a whole, the CFS Building presents a major technological, space, and visual upgrade.

A natural area park in the undeveloped property surrounding the basin will provide a beautiful habitat for native flora and fauna.

Our facilities planning efforts included evaluation of CSO reduction measures and upgrade alternatives for the existing 57-mgd Paerdegat Pumping Station. The criteria used to select the most effective facilities plan included constructability, compatibility with existing conditions, beneficial impacts on receiving water quality, environmental impacts, capital costs, operation and maintenance costs, and present worth and equivalent annual costs.

Retained combined sewage is pumped to the gravity interceptor via two discrete transfer systems. The first includes three 135-hp vertical centrifugal CSO pumps, each rated for 16.8-mgd. The other system has two 85-hp pumps, each with a nominal 3.6-mgd capacity, to handle the slurry of combined sewage and settled solids in the offline storage tanks.

During storm events, approximately 30 million gallons of CSO volume is stored offline in the CSO retention tank and tank influent channels, and an additional 20 million gallons is retained in the sewers. Approximately half of the tank’s volume is emptied by gravity to a nearby interceptor sewer and the remainder is pumped.

After each storm event, the tank is cleaned using a system of 48 flushing gates. Located at each end of the storage tank, the gates open sequentially to release controlled amount of water and create hydraulic wave action to push settled solids to the wet well, which is then pumped by the grit pumps described above.

All incoming flow is screened prior to entering the storage tank. The screening facility is designed to pass flow of up to 2 billion gallons/day and to remove large size debris and floatables using six 9-foot wide reciprocating rake (climber) screens. Collected screenings are transported via molded-pan belt conveyor to a storage container for ultimate off-site disposal.

The CSO tank and all process areas are ventilated and receive odor control. The odor control system consists of five exhaust air trains, each containing motorized inlet and outlet damper, activated carbon vessel and variable speed fan. Each carbon vessel is designed for 36,000-cfm max flow and the fans are 150 hp each.

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

Peter Young, P.E. at