Concord task force narrows three dredging alternatives for Warner’s Pond, flags arsenic and permitting constraints

Co-chair Chris Dennaro and the task force’s dredging subgroup on the evening presented three alternatives for removing sediment from Warner’s Pond: a baseline plan to remove about 35,800 cubic yards, a medium option of about 50,000 cubic yards and an expanded plan of roughly 100,000 cubic yards. The subgroup said all options would retain an approximately 1-acre wetland shelf and that deeper dredging (moving from an initial 9-foot target to up to 12 feet in places) would help create cooler, deeper water and slow invasive-plant regrowth.

The presentation identified a nearby 10-acre parcel the team calls “Northfield” as the primary staging and dewatering site for dredged material. The subgroup said 10 test pits at Northfield showed upland soils with no shallow groundwater and that removing topsoil would provide roughly 49,500 cubic yards of capacity before any additional excavation. The subgroup also described a possible partnership with a third party (identified in the presentation as Bruce Thompson/De Maximus) that has expressed interest in taking tens of thousands of cubic yards for another project; the presenter said such a partner could cover excavation and trucking costs and thereby increase available staging capacity.

The project team told members that new sediment chemical analysis is required before final disposal plans can be confirmed. “We just need to make sure to do that again,” the presenter said, adding that “some of it may exceed arsenic criteria and, you know, may require transport somewhere else.” The task force recalled earlier samples that showed slightly above-reportable arsenic concentrations in a southeast portion of the pond and estimated that about 5,000–6,000 cubic yards might need handling as contaminated material if confirmed.

Members stressed two technical and regulatory constraints. First, deeper or larger footprints will change the permitting picture: presenters said expanded dredging and increased depth would require updated state and federal permits and that the permitting process can take on the order of a year. Second, emerging PFAS guidance may affect disposal options: members asked that PFAS be included in new sediment testing because evolving regulation could limit where dredged materials may be placed.

The subgroup said it will issue a request for information (RFI) to contractors to get cost estimates for each alternative and to solicit rough designs for moving the Route 2 stormwater outfall (a 30-inch drain noted in the presentation) off the pond and, if feasible, onto Department of Corrections (DOC) property. Presenters said DOC had provided verbal assurances that it could accept material but that a formal memorandum of understanding would be required before any material movement. Task force members asked staff to clarify ownership, confirm any necessary DOC agreements, and identify whether DOT or other agencies would need to be notified.

Members also discussed engineering details — the dredge will be sloped rather than uniformly dug to a fixed depth, pipes to pump slurry can cross the Bruce Freeman Rail Trail with temporary ramps, and side-cast or pipeline approaches could move dredged material short distances or up to miles where needed. The task force emphasized that final recommendations will depend on RFI cost estimates, the results of updated sediment chemistry testing (including arsenic and PFAS), confirmed site agreements for Northfield, and permit outcomes.

The group did not take a formal vote on any dredging alternative on the night; instead the subgroup will refine the RFI and provide cost estimates in the coming weeks. The task force agreed to continue discussing disposal feasibility, contaminant management, and how fish-passage or dam-related improvements might be paired with dredging.