Forge River Watershed Sewer Project

Communities affected by the Forge River Watershed Sewer Project know all too well the environmental and public health risks that come with flooded septic systems. Onsite septic systems and cesspools provide sanitary wastewater disposal for approximately 70% of the 1.5 million residents of Suffolk County, New York.

Over many decades, an aging septic system and cesspool failures created a nitrogen pollution crisis in the Mastic-Shirley area. This pollution is degrading surface and groundwater quality, affecting the Forge River Corridor and Great South Bay. Many onsite systems failed in 2012 during Superstorm Sandy. These system failures further exposed the urgent need to upgrade local infrastructure to protect the vulnerable coastal communities on Long Island from the impact of future intense storms and weather events.

The Forge River Watershed Sewer Project is the largest sewer collection system program undertaken by the Suffolk County Department of Public Works in the past 40 years. Started in Sept. 2016, the $223.9 million project will provide a new sewer collection and conveyance system and an advanced wastewater treatment facility (AWTF) to mitigate the harmful impacts of onsite septic system and cesspool failure, especially during flooding and heavy rain events. Additionally, the new system and AWTF will help reduce the adverse impacts of high levels of nitrogen in the ground and surface waters and coastal wetlands caused by cesspool and septic systems failures. This improvement will provide natural protection against storm surges.

Once completed, the new AWTF, located in Mastic, Town of Brookhaven, New York, will serve nearly 1,900 developed residential parcels in the Mastic-Shirley area, thereby eliminating the use of existing septic systems. The Forge River Watershed Sewer Project is one of three projects included in the $408.8 million Suffolk County Coastal Resiliency Initiative. This project will connect more than 5,368 homes to sewer systems to reduce nitrogen loading, improve water quality, and enhance storm resiliency by building back natural coastal barriers.

Gannett Fleming is providing planning, design, and construction management services to Suffolk County for the Forge River Watershed Sewer Project, including the new sewer collection and conveyance system and the 1 million gallons per day AWTF.

Design drawings were prepared using Building Information Modeling (BIM) to integrate multidisciplinary data and develop detailed digital representations of the facility and its equipment. BIM was also used for creating and managing data during the design, construction, and operations process.

Our firm’s work included preparing a map and plan report, which details the proposed service area comprised of approximately 2,450 parcels and the sewer infrastructure design. The report also included the financial impacts on the community associated with the formation of a new sewer district.

In January 2019, the majority of the property owners within the new sewer district provided their consent via a public referendum to create the sewer district. To accomplish this, Gannett Fleming developed and implemented extensive stakeholder outreach and education programs consisting of public information open houses, educational flyers, and a project website to help residents understand the benefits of the new sewer system versus the traditional septic systems. The open house sessions allowed the public, project team members, and stakeholders to interact and also provided opportunities for the project team to answer questions and explain various project aspects.

Our community outreach efforts informed residents of the advantages of low-pressure sewers with individual grinder pumps, as compared to gravity sewer systems with intermediate pump stations for the new sewer district, based on the following advantages:

• Construction costs are reduced by 25%-30%.
• Small-diameter pipe and trenchless construction methods are used.
• Fewer road closures during construction.
• Construction of the system is independent of topography.
• System is cost-effectively installed in areas that are flat and have a high-groundwater table or are along coastal areas.
• Subsurface soil conditions are not a factor.
• Fewer change orders are required as subsurface interferences, such as existing utilities and pipelines, are easily avoided in developed areas.
• Overall infiltration/inflow reduction.

Gannett Fleming also prepared detailed engineering design reports for the low-pressure sewer system and the AWTF, per regulatory requirements. As part of the design process, the project team performed a property investigation of each parcel to define the existing conditions, locate the existing on-lot sewage disposal system and surface features, and find the optimum location for the new grinder pump unit installation.

Federal, state, and local regulatory permits were obtained for the construction of the new facilities. Ten sets of contract bid documents were prepared, including the AWTF (1), Low-Pressure Sewer Mains (3), and Grinder Pump Installations and Residential Customer Connections (5). Construction of the AWTF began in 2022 and will be completed in 2024. Construction of the low-pressure sewer system began in 2022 and is expected to be completed in 2024. The installation of the grinder pump units and connection to the low-pressure sewer mains are expected to begin in 2024 and be finished in 2026.

The projected completion year for the Forge River Watershed Sewer Project is 2026. When finished, this critical wastewater infrastructure initiative will reduce nitrogen loading, improve water quality, enhance storm resiliency by building back natural coastal barriers, and improve the quality of life for Long Islanders for many generations to come.

• Project reduces nitrogen loading, improves water quality, and enhances storm resiliency by building back natural coastal barriers.
• AWTF with 1 million gallons per day capacity mitigates harmful impacts during major island weather events caused by onsite septic systems and cesspool failures.
• New AWTF will serve nearly 1,900 developed residential parcels eliminating the use of existing septic systems in the Mastic-Shirley area.
• BIM was employed to develop design drawings to integrate multidisciplinary data with detailed digital representations of the facility and its equipment.
• Extensive community outreach efforts provided residents with information to help them understand the benefits of the new sewer system versus the traditional septic systems.

• Long Island Business News Real Estate, Architecture & Engineering Awards, 2023, Top Infrastructure Project.