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Engineers recommend culvert replacement, road-raising to protect North Haven’s Fresh Pond
Summary
CV Mahar Engineers presented a feasibility study recommending replacing the existing culvert with a 36-inch HDPE pipe, raising Middle Road from elevation 13 to 15, and installing duck-bill backflow devices to reduce saltwater intrusion into Fresh Pond. Preliminary cost estimates are roughly $200,000–$250,000; next steps include a survey, wetland permitting steps and coordination with town water and fire personnel.
CV Mahar Engineers presented preliminary design options aimed at protecting Fresh Pond, North Haven’s freshwater drinking supply, from saltwater intrusion and more frequent storm events.
"After our review, we believe option C is the best option to protect Fresh Pond from saltwater intrusion," said Jeff Reg of CV Mahar Engineers, who led the presentation. He described reviewing a 2022 Ransom study, field visits, and a wetland delineation performed by Alfrick Associates as part of the evaluation.
The firm said it dismissed options that would raise or alter Fresh Pond’s water surface elevation. Instead the recommended path — described in the study as C2 — keeps the pond elevation unchanged, replaces the aging corrugated metal culvert in-kind with a roughly 36-inch HDPE culvert, and raises the adjacent section of Middle Road from elevation 13 to elevation 15 to add freeboard and reduce overtopping and saltwater ingress.
Reg described backflow-prevention devices (a duck-bill style valve) as a simple, low-maintenance way to stop seawater migrating through the culvert during high tides or storm surges. "A single device mounted inside the culvert is going to be cost-effective and long-term," he said, adding that the valves have an expected service life of about 20 years.
The engineers flagged local maintenance challenges the town should address in design: beaver-related clogging, the need for trash racks or inlet structures, and how the culvert invert and inlet boards currently affect the water department’s intake during summer low-water conditions. Aaron Cav of the road crew told the group the current culvert is about a foot lower than designed and cited ongoing field maintenance needs.
The firm provided an early cost estimate range of approximately $200,000 to $250,000 for the project, noting that design refinements and reduced contingencies could change the number. "We thought this was going to come in just under $200,000 ... we're thinking in the quarter-million dollar range at this point," Reg said.
Permitting steps were discussed: the engineers said they expect to initiate a pre-application meeting and a pre-construction notification with the US Army Corps of Engineers, and they suggested the work might qualify as a "permit by rule" (as noted in the presentation). If the project footprint expands and wetlands are impacted, the permit requirements could escalate to a higher tier.
Board members and island residents asked about environmental impacts — including eel and fish migration, downstream effects on the salt pond, and whether raising Fresh Pond’s elevation would change salinity. Reg replied the team will examine stream-wide impacts in later design stages and that outlet structure geometry will control water exchange between ponds.
Board members also discussed operational elements that could be folded into the project, including adding a dry hydrant at the same site to improve fire response. The engineering team said they will follow up with survey work, wetland permitting outputs, and further cost refinements and will meet with the water and fire departments as part of next steps.
The select board did not take any formal vote on design authorization at the meeting; the engineers said they will return with refined plans, cost details and permitting guidance for future board action.
