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City staff recommend buried secant pile wall for Bull's Pond dam after multi-option review
Summary
At a lengthy June 17 presentation, Newton staff and consultants laid out four alternatives for the Bull's Pond dam — dam removal, new core-wall dam, buried secant (secant pile) wall, and downstream erosion protection — and recommended a buried secant pile wall as the best balance of upfront cost, longevity and breach-risk reduction while acknowledging community opposition and downstream culvert capacity constraints.
Chief Operating Officer Josh Morris presented a high-level review of four alternatives for the Bull's Pond dam project to the Public Facilities Committee on June 17, saying the session was informational and not for a vote.
Morris said the working group and consultant GEI focused on four final alternatives: (1) dam removal, (2) a new core-wall dam, (3) a buried secant (secant pile) wall dam constructed downstream of Dexter Road, and (4) downstream erosion protection using articulated concrete block. He described trade-offs among upfront cost, life-cycle cost, breach risk and downstream impacts that hinge on the capacity constraints of Laundry Brook’s culvert network, which Morris said is undersized for flows that would follow dam removal without substantial additional downstream work.
Morris summarized consultant estimates presented in the backup materials: a dam-removal upfront estimate of roughly $16.2 million to $22.1 million but with life-cycle costs that could be much higher when accounting for downstream culvert upgrades, ongoing sediment/dredging, and potential legal costs and property-value impacts; a new core-wall dam estimated at $13.9 million to $18 million (75–100 year lifespan); and a buried secant pile-wall dam estimated at $8.44 million to $11 million with the lowest modeled breach risk. Downstream erosion protection had the lowest upfront price (roughly $3M–$4M in the presentation) but carried a high maintenance burden, a shorter expected life and a higher long-term risk of failure that could lead to a breach if not meticulously maintained.
Morris emphasized modeling that showed dam removal could increase downstream flooding risk in some storms (largely 25-year and smaller events) because the existing Laundry Brook culvert system is constrained along a roughly 2.1-mile buried route to the Charles River. He also described analysis by the assessor’s office that estimated reductions to assessed value in properties abutting the pond in some scenarios and cautioned that legal challenges could add significant unquantified costs to a removal path.
After discussing the criteria matrix, Morris said the working group, the consultant and the city engineer overwhelmingly recommended the buried secant pile-wall alternative as the option that balances construction cost and long-term risk and aligns with many residents’ expressed preferences. Councilors pressed staff for more information on tree-removal magnitude, how the buried wall would relate to the existing spillway, timing and construction logistics, the potential for a new low-level outlet to provide proactive pond-level management, and the extent and timing of downstream culvert or stormwater investments.
Staff said GEI will provide more detailed hydrologic and hydraulic models on request (the Charles River Watershed Association requested access), and that the administration intends to return with more detailed design and cost refinements before any formal vote. The committee voted to keep the item in committee for additional analysis and public engagement.
