Weston ZBA Hears Conflicting Groundwater Models on South Avenue 40B Project

WESTON — May 2, 2022 — Weston ZBA hears unresolved groundwater and water quality disputes over a 200-unit Chapter 40B rental proposal on South Avenue. Board peer reviewer Matt Davis told the Zoning Board of Appeals that seasonal high groundwater exceeds the applicant's modeled threshold in six of the past 10 years, not the rare condition the applicant has claimed, and that the ModFlow model fails to account for infiltration system backups under storm conditions. Abutter consultant Michael Moble of McDonnell Morrissey ran the applicant's own model with 25-year and 100-year storm inputs, producing simulated mounding peaks of nearly 26 feet and more than 30 feet respectively above proposed grade near stormwater infiltration area three — results he described as physically unrealistic but "a pretty clear demonstration" that HydroCAD and ModFlow are "fundamentally disconnected." Water quality reviewer Scott Horsley noted the project's proposed wastewater flow of 26,000 gallons per day at 80 percent capacity would outstrip the receiving stream's 7Q10 low flow of roughly 3,800 gallons per day by a factor of seven, with no formal water quality impact analysis yet submitted. Applicant engineer Charlie Head and Dr. Tom Ballestero maintained that Massachusetts regulations do not require mounding analyses for larger storm events where four-foot groundwater separation exists and that bypass provisions protect against overflow. The hearing continues May 10 on stormwater and civil engineering, and May 17 on wetland impacts.