NHDOT outlines plan to replace red‑listed culvert on Gilsum Road with prefabricated bridge

Selectman Jay Croteau and his fellow selectmen met with GM2 representatives for the New Hampshire Department of Transportation to review Project 44409, a plan to replace the red‑listed metal culvert on Gilsum Road over Thompson Brook with a prefabricated concrete bridge.

Tom Levin and Jason Tremblay, GM2 representatives working with NHDOT, said the existing culvert was red‑listed in 2017, carries a sufficiency rating of 52.8% and has a condition rating of 3 (serious). They described a proposed prefabricated concrete span roughly 30 feet long and 30 feet wide, with widened approaches to improve aquatic passage and to comply with NHDES stream‑crossing rules.

Levin and Tremblay said the department prefers Accelerated Bridge Construction (ABC). Under that plan, Gilsum Road would close for approximately one month within a single construction season; an alternate approach using an offline temporary bridge could extend work over two construction seasons. The presenters identified spring, summer or fall 2028 as preferred timing windows and said planning will include provisions for mutual aid, school and bus routes, emergency response access and bicycle and pedestrian accommodations.

The presentation addressed natural‑resource and historic‑resource considerations. DOT staff described Thompson Brook as a Tier 3 cold‑water fishery and noted the nearby Ashuelot River is a designated river and essential fish habitat for Atlantic salmon. LAC was contacted, DOT said, and staff reported the site is not eligible for historic registration and is exempt under the program comment for common post‑1945 concrete and steel bridges; a Section 106 request to the New Hampshire Division of Historical Resources has been submitted for review.

Agency staff flagged potential species concerns: the federally endangered long‑eared bat and the federally proposed monarch butterfly were noted near the corridor, and ARLAC’s Barbara Skuly raised a concern about the dwarf wedge mussel but said none had been found at this location. DOT said environmental reviews and permitting will be part of the NEPA process.

Resident John Davis urged the board and DOT to address remediation of existing debris and buildup that could hinder flow, requested a post‑construction invasive‑species planting and management plan, and said a local event (the Del Mar Marathon in September) could be affected by road closures. Bruce Smith provided local historical context for features near the site, and DOT noted stonewalls and stone foundations nearby.

DOT representatives also reported there is no 100‑year floodplain map at the bridge site and said abutters will be notified as planning proceeds.

Next procedural steps, the presenters said, are to complete NEPA, hold a public information meeting several months from now to gather input and to develop alternatives based on that input. The selectmen and DOT emphasized that details on closures, detours and emergency access would be refined during design and permitting.