Southampton advances $44 million Riverside sewer plan toward construction

Southampton moved the $44 million Riverside sewer plan a step closer to construction Tuesday, but consultants said the system is still only about 60% designed and may not begin service until late 2029 or early 2030.

At a meeting at the Flanders Community Center, residents were shown how the project would work, including grinder pumps at each property and a low-pressure network that would move wastewater to a new treatment plant. For Riverside, the delay matters now: the hamlet’s shallow water table and decades of dependence on septic systems have limited investment, and the sewer district is meant to change that.

Town officials have cast the project as the backbone of Riverside’s long-running revitalization effort. Southampton’s 2015 Riverside Revitalization Action Plan and Riverside Overlay District zoning were written to allow higher-density mixed-use development in the hamlet, and town documents say the sewer plant and collection system are critical to making that plan real.

The newest design also shows how much the concept has been trimmed to fit local conditions. Consultants said the treatment plant has been reduced from an original 800,000 gallons per day to 290,000 gallons per day because of hydrologic constraints and the impracticality of the earlier wetland-based approach. The current redevelopment vision calls for roughly 532 housing units and 198,000 square feet of commercial space, with room for offices, retail, restaurants, a grocery store and other small businesses. In the earlier planning era, the broader concept had envisioned as many as 2,300 housing units.

The sewer district also picked up major financial support last fall, when Southampton received a $19 million federal grant tied to the Infrastructure Investment and Jobs Act. Town officials said the money would help remove thousands of pounds of nitrogen from local waterways each year and push the project closer to construction after a roughly $5 million shortfall surfaced in March 2025.

Southampton Town Planner Janice Scherer said in March that permitting and construction would not begin until mid-2027 and that completion should come in 2030. The latest design update suggests the schedule is still tight, and the town will have to turn the current 60% design into a bid-ready project before property owners can expect hookups or relief from the septic-era limits that have constrained Riverside for years.

The project has also remained politically fraught. Riverhead Town has argued that county facilities in Riverside, including the Suffolk County Center, the Arthur M. Cromarty Criminal Court Complex and the Riverhead Correctional Facility, should be included in the sewer district because those parcels have been served by Riverhead’s wastewater system since 1969. Riverhead authorized and filed suit to challenge Southampton’s district boundaries, but a Suffolk County Supreme Court judge dismissed that case in October 2025.

With the supplemental final generic environmental impact statement accepted in April 2024 and public hearings already held in December 2023, January 2024 and February 2024, Southampton is now past the planning debate and into the harder test of delivery. Riverside’s future, and the water quality of the Peconic River corridor beside it, will depend on whether the town can keep the schedule from slipping further.