Board approves three stormwater waivers for Mills Middle/High School addition after peer review

Engineers and the construction manager presented plans for an addition and renovation at the Mills Middle and High School, describing new closed drainage, bioretention rain gardens, subsurface infiltration sized for a 100‑year storm, a new fire loop and a 6,000‑gallon grease trap for the renovated cafeteria. "There is no real closed drainage system other than some roof leaders; much of the stormwater currently runs off untreated toward the wetlands," engineer Michelle Palan told the board.

A peer reviewer from the Beta Group, Steve Lee, told the board his team found the design sound overall but flagged several regulatory waivers and recommended the town observe subsurface materials before final acceptance. "We provided a comment about making sure that there's a specific note about signs saying danger and keep out around any excavated areas," Lee said.

After discussion the board voted to grant three waivers requested in the EHIR: a waiver from section 12.1 to allow a net decrease in off‑site runoff volume and rate, a waiver from section 12.4 to allow 3:1 side slopes and flatter basin bottoms in bioretention rain gardens (in lieu of the 4:1/2% requirement), and a waiver from section 12.5 accepting the applicant's laboratory/test‑kit soil documentation in place of on‑site NC2 borehole permeability testing. The board and consultants recorded conditions to stabilize slopes during construction, to provide cross‑sections and erosion controls, and for the town to observe key subsurface installations.

Staff said a final EHIR and a consolidated set of documents will be prepared for the board's signoff before filing; the consultant agreed to return with a final report at the July meeting. The board and consultants also discussed phasing logistics including temporary access, soil export estimates and temporary parking plans for when school resumes.

The board's approvals allow the project to proceed toward final engineering and permitting steps, subject to the standard conditions discussed in the peer review and the town's ongoing oversight.