Words could not describe the destruction to wetlands along parts of Buzzards Bay and all of Mattapoisett Harbor, should the Eel Pond forced main become compromised. That possibility has been discussed for years when considering what can be done to improve the infrastructure for flow of sewage from Mattapoisett to the Fairhaven treatment facility via the Eel Pond forced sewer main.
Natural tidal shifts and storms have been shaping and reshaping the seabed in and around what’s known as the Eel Pond breach for decades. There have been concerns over the exposure of the forced sewer main, built in 1977 across the breach, almost since the beginning. The 12-inch-wide sewer line stretches 1,400 linear feet across the channel. After receiving a grant in the sum of $119,486 from Coastal Zone Management, an up-to-date study now brings improvement options into focus. Building on studies that took place between 2001 and 2017, engineering firm Tighe & Bond held a public meeting on August 5 to announce its findings.
Part of the presentation delved into the history of the environmentally sensitive wetlands associated with Eel Pond, wetlands that have recently been part of Phase1b of the bike path with the construction of a massive pedestrian bridge. Studies prepared by the Massachusetts Department of Transportation for the recreational path project were incorporated into the Tighe & Bond evaluation. All technical input pointed to the necessity of running a new sewer line sooner rather than later.
“We expect the Eel Pond inlet to continue shifting south-southwest over the next 50 years as its done for the past 50 years,” the engineering team advised. They determined that a new sewer line at least 16 feet below the surface was needed.
The engineering team detailed various construction options from spanning Route 6 where the Mattapoisett River crosses the highway to various themes on crossing the marshlands surrounding the pond and the barrier beach at Goodspeed Island. Only one plan was believed to be the most viable, while all plans presented constraints.
Plan 1 would send the sewer line over the existing Route 6 bridge for a cost estimate of $4,381,000. Plan 2 is an open-cut excavation plan with a cost estimate that was not disclosed, as this plan is not being seriously considered given the wetlands impact.
Plan 3 is a parallel, horizontal-directional drilling option that would require new easements with a cost estimate of $2,210,000. Horizontal Directional Drilling, an electronically guided boring practice, has already been successfully used by the Water and Sewer Department when sewer was introduced along a beach neighborhood in the community. The process “…minimizes wetland and resource impacts,” the study showed.
And Plan 4, the preferred plan, is a horizontal-directional drill under Eel Pond and the salt marshes using, for the most part, existing easements for a cost estimate of $2,345,000. In all estimates, any necessary acquisition of new easements was not part of the calculations.
Plan 4 touts as benefits, “lesser impact to resource area, alignments of sewer line less susceptible to long-term coastal processes, allows for deep installation of force main below projected scouring depths, and avoids the bike path currently under construction with a shorter construction period.
Constraints associated with Plan 4 include, “the need for a larger area for horizontal direction drilling rig setup and pipe pull-back process, the potential for mud fracking, and the need for both temporary and permanent new easements.
In a follow-up with Mattapoisett Water and Sewer Department, Director Henri Renauld said, “We want to try and stay as much as possible within the easements we have; it’s cost-effective.” Renauld also said that with the remaining grant monies will be the continued coordination between the town’s representatives and such agencies as local boards, Mass DEP, Army Corps of Engineers, Marine Fisheries, the Executive Office of Environmental Protection and Coastal Zone Management, as well as others. He said that moving forward, alternatives would be presented to these agencies in the hope that the final plan will receive additional grant monies by spring 2021.
Mattapoisett Water and Sewer Department
By Marilou Newell