Smithtown, NY Environmental Rules: Stormwater Management (2026)

Under Chapter 153, no site plan, subdivision, building permit, tree-clearing permit or Chapter 154 permit can be granted for a land development activity without the Stormwater Management Officer (the Town Engineer or a designee) first reviewing and approving a stormwater pollution prevention plan (SWPPP), per Smithtown Code § 153-8A. A SWPPP must include a post-construction stormwater management component whenever the activity discharges to a state-listed impaired water, disturbs five or more acres, or disturbs between one and five acres outside single-family and agricultural work (§ 153-8B(2)).

That component has to show hydrologic and hydraulic analysis for the applicable design storms, compare pre- and post-development runoff, and lock in maintenance easements recorded against the property (§ 153-8B(3)). Designs built to the New York State Stormwater Management Design Manual and the state Erosion and Sediment Control Manual are presumed compliant; anything else must demonstrate equivalence (§ 153-9A, B). Separately, no land development activity may raise turbidity to a level causing substantial visible contrast to natural conditions in Town waters (§ 153-9C). Once built, permanent facilities need a preventive maintenance program, written operating procedures, and a formal maintenance agreement recorded with the Suffolk County Clerk as a deed restriction before final plan approval (§ 153-10C, D).

The Town may instead accept dedication of the facility if it meets the chapter's standards and includes perpetual access for inspection (§ 153-10D). Fees for SWPPP review, inspections and maintenance oversight are set by the Town Engineer's fee schedule and credited to a dedicated Stormwater Management revenue account (§ 153-15).