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Task force hears contractor say nearby dredged sediment could be reused as structural fill if it meets strict testing
Summary
Consultant Bruce Thompson told Concord’s Warner’s Ponds Task Force that dredged pond sediments might be usable as engineered backfill at a nearby remediation site if they pass site-specific geotechnical and chemical tests; the group discussed sampling frequency, transport costs and timing for any reuse.
Bruce Thompson, a Maximus consultant who joined the Warner’s Ponds Task Force meeting by phone, said dredged pond material could be reused as engineered backfill for an ongoing remediation project if it satisfies both geotechnical compatibility and the site’s chemical cleanup levels. "We have very, very low PAH ... like at a 0.25 part per million," Thompson said, describing the tight chemical limits his site requires.
Delia, a task force member who outlined the group’s options, said the subgroup is evaluating dredging, dam removal and other alternatives and is considering using an unrestricted field on DOC-managed land west of the prison parking lot (the "Northfield") to accept dredged material. Thompson said reuse would require site-specific geotechnical testing (bearing capacity, compaction) and chemical verification, and that verification sampling would likely be required on the order of one sample per 5,000 cubic yards.
Thompson described a multi-year schedule for his remediation program: limited excavation and other site work in the near term, a slurry wall installation the following year, and a larger tranche of excavation about three years out. He said his contractors usually price imported fill per ton delivered and build characterization work into vendor bids. "A good chunk of the cost is transportation," Thompson said, adding that a nearby borrow source would reduce diesel and hauling costs and make reuse more likely to be cost-effective.
Task force members pressed on logistics: whether topsoil would be needed for final capping, whether a temporary stockpile could be staged, and who would pay excavation and transfer costs. Thompson said his program needs both structural fill and topsoil (including a 6-inch topsoil cap) and that contractors typically cover characterization and transport costs as part of their pricing. He also said he is willing to pursue precharacterization with EPA and to coordinate on timing if the task force identifies a defined borrow area.
Why it matters: reusing locally dredged material could lower disposal and hauling costs and reduce emissions compared with importing quarry material. But it requires meeting very low chemical acceptance criteria, documented geotechnical suitability and formal approvals by regulators, including EPA, Thompson said.
Next steps noted by the task force: confirm specific volumes and depths to be dredged, identify sampling and precharacterization needs for the proposed Northfield borrow area, and coordinate timing so the remediation program’s excavation schedule can align with dredging operations. The task force did not make a formal decision to move sediment off-site; members agreed to include disposal-location options in upcoming procurement materials and to pursue additional technical analyses.
