Engineer: proposed drainage for 580 Valley Road would far exceed code minimums

Gerard Desario, the applicant's civil engineer, told the Planning Board the revised site plans add a trench drain and an underground infiltration basin intended to capture runoff that now flows to the municipal parking lot.

"The requirement per the ordinance is that we only need to maintain or manage 736 cubic feet of runoff on‑site," Desario said. "What we're proposing is a system that has 3,794 cubic feet of storage volume," he added, explaining that the design equates to roughly 4 inches of runoff across the 0.36‑acre property and, with minimal infiltration, would perform to between a 10‑ and 15‑year design storm.

Desario cautioned, however, that flash flood events—short, intense storms—are not captured by standard 24‑hour rainfall design classifications. "It's not gonna cure any flooding that happens in municipal parking lot, but it's certainly gonna be a huge benefit to it," he said, noting the system will significantly reduce volume reaching the lot but cannot eliminate all municipal flooding risks.

Board members and members of the public accepted the engineering explanation but asked for follow‑up soil testing, confirmation of infiltration rates during construction, and conditions in the Naglier engineering report to be incorporated as approval conditions. The applicant agreed to comply with outstanding engineering conditions and to provide additional exhibits ahead of the Sept. 14 continuation.

The board asked the applicant to document remaining outside‑agency approvals and to submit soil testing data prior to final construction approvals.