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Concord task force presses for firm pond elevations, debates dredge volumes and disposal options
Summary
At a Sept. 3 task force meeting, public commenter Dan Stapleton and members pressed consultants for absolute pond-bottom elevations (NAVD88) after finding depth-to-elevation inconsistencies; the group revisited 14,000 vs. 35,000 cubic-yard plans and weighed in-pond placement versus Route 2 field disposal.
Public comments and technical discussion at the Town of Concord Dredge Task Force meeting on Sept. 3 centered on whether the dredge bid and alternatives analysis used correct absolute elevations for the pond bottom, a detail speakers said is critical to setting dredge targets and estimating quantities.
Dan Stapleton, a member of the public who said he submitted more than 300 pages of supporting documents, asked the task force to obtain absolute pond-bottom elevations referenced to the North American Vertical Datum of 1988 (NAVD88). "What is the elevation of the bottom of the pond?" Stapleton asked, noting consultants reported depths relative to water surface but did not fix those depths to a common survey datum. He warned that a datum or contour mismatch (he used hypothetical examples such as Elevation 112 vs. 114) could materially change bid quantities and design outcomes.
Task force members agreed the datum question is essential. One member said EA will be asked to clarify the elevation conversion and to provide the requested volume information for the alternate disposal location being evaluated. Members noted the most detailed pond-bottom contours in their files are the dredge bid package, while dam-rehabilitation drawings have only limited overlap.
The group revisited earlier volume figures. The dredge bid and alternatives analysis had different estimates: a 35,000 cubic-yard plan in earlier work versus a reduced 14,000 cubic-yard proposal in the most recent bid. Several members said 14,000 cu yd would likely leave too small an area cleared of invasive aquatic plants to meet ecological goals; others urged the task force to define desired dredge area and depths first and then "back out" cost estimates rather than starting with a budget cap.
Members and the public discussed disposal options. EA had proposed a field placement location near Route 2; speakers asked the firm to assess in-pond placement to reduce haul and management costs, and to confirm whether the Route 2 fields could physically accommodate the quantities under consideration. One participant noted that in-pond placement and off-site field placement are different operations with divergent cost profiles and environmental implications.
Technical clarifications raised included: the pond's normal pool elevation (cited by a public speaker as approximately 118.8), a practical minimum dredge depth recommended by several members (about 8 feet to limit light penetration and submerged aquatic vegetation), and estimated sedimentation rates referenced in the meeting (one speaker cited roughly 40–60 cubic yards per year arriving from upstream).
Next steps recorded by the task force included asking EA to provide: 1) the elevation-converted pond-bottom contours tied to NAVD88, 2) a volume estimate for the alternate disposal field near Route 2, and 3) cost estimates for at least three quantity scenarios (including a 35,000 cu yd baseline). The group also discussed hiring a third-party construction-cost estimator with dredging expertise and performing test pits at the Route 2 field to establish loam depth and capping requirements.
The meeting produced no formal votes or motions on dredging; members agreed to seek clarification from consultants and reconvene with the information.
