Nashua, NH Environmental Rules: Stormwater Management (2026)

Chapter 190 Article XXXI applies to any subdivision plan or site plan in Nashua and requires a stormwater management and erosion control plan reviewed by the Planning Board. The water-quality treatment standard distinguishes between discharges to the Water Supply Protection District (the Pennichuck Brook watershed, which supplies Nashua's drinking water through Pennichuck Water Works) and all other discharges. For discharges to the Conservation Zone within the Water Supply Protection District, the runoff volume to be treated for water quality is calculated as 1.0 inch of runoff multiplied by the total impervious area; for all other discharges the water-quality volume is 0.5 inch of runoff multiplied by the total impervious area. For new developments, stormwater management systems must be designed to remove 80 percent of the average annual load of total suspended solids (TSS), floatables, greases, and oils after the site is developed. Redevelopment of previously developed sites must meet the stormwater management standards to the maximum extent possible, with the goal to reduce impervious area by a minimum of 20 percent or meet the open-space requirement in the underlying zoning district. The Planning Board may waive all or part of the stormwater plan requirement if it determines a plan is unnecessary because of the size, character, or natural conditions of a site. Nashua's MS4 permit obligates the city to implement six minimum control measures including public education, illicit discharge detection and elimination, construction-site runoff control, and post-construction stormwater management, and the city files annual reports with EPA Region 1 and NHDES. Large land disturbance projects (more than 100,000 contiguous square feet, or more than 50,000 square feet within a protected shoreland) require a separate Alteration of Terrain (AoT) permit from NHDES under RSA 485-A:17 and Env-Wq 1500.