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Consultant recommends NOAA Atlas 14, lowers disturbance threshold in proposed stormwater overhaul
Summary
A consultant told the Village Board the proposed PLLU 2025 would adopt NOAA Atlas 14 rainfall data, move stormwater rules into zoning, and require erosion-and-sediment controls for land disturbances between 200 and 1,000 sq ft, with waivers tied to engineer calculations and emphasis on green infrastructure sized for the first inch of runoff.
Jim Moran of H2M told the Village Board that the proposed PLLU 2025 would move stormwater rules currently in chapter 294 into the zoning code and update technical standards to reflect recent rainfall data and practice. “The NOAA Atlas 14 is the latest data… the intensities are higher,” Moran said, adding that the draft incorporates Atlas 14 and other updated criteria.
The draft lowers the threshold for a stormwater pollution prevention plan from 1,000 square feet of land disturbance to the 200–1,000 sq ft range and focuses those requirements on preconstruction and during‑construction erosion and sediment controls rather than post‑construction detention systems. Moran said that for smaller disturbances, the code is better focused on preventing erosion during work rather than requiring engineered detention that many small sites cannot practically meet.
Trustees asked how protective the Atlas 14 data is compared with the village’s prior standard; Moran said Atlas 14 is continuously updated from local rain gauges and generally produces higher intensity values used for design. He described a waiver process for sites where infiltration is infeasible: an applicant’s licensed engineer would submit calculations demonstrating infeasibility to qualify for exceptions.
Moran also recommended including green infrastructure practices sized to capture the first inch of rainfall rather than higher retention rates. He said many green infrastructure practices — for example, rain gardens — are typically designed to retain the first inch of runoff and that requiring 1.25 inches would make those practices impractical. “Most green infrastructure practices… are only able to retain the first inch of runoff,” Moran said. The consultant recommended reducing a local retention standard from 1.25 inches to 1.0 inch to align with typical practice.
Board members raised practical concerns about thresholds and property impacts, asking whether the code should account for parcel size when allowing a 5% increase in existing structure size, and whether patios or small renovations might be unduly burdened. Moran said the revised approach focuses on land‑disturbance increase rather than post‑construction impervious area increases.
The board did not take a vote; staff will refine language and return the draft for public hearing scheduling and a referral to Westchester County planning for zoning changes where required.
