St. Tammany Parish, LA Environmental Rules: Stormwater Management (2026)

Section 900-6.9 sets the parish's stormwater quality and illicit discharge program, run by the Parish MS4 Administrator under subsection B.2. It bars anyone from introducing an illicit discharge, meaning any non-stormwater discharge, into the MS4, drainage infrastructure, conveyances, or waterways of the parish, and separately bars any discharge that causes or contributes to a water quality standard violation, under subsection C.1-2. Subsection D lists specific banned discharges, including used motor oil and other vehicle fluids, industrial or household hazardous waste, untreated sewage or septic waste, grease or grit trap waste, concrete or asphalt base material, uncontrolled construction sediment, and direct discharges of pesticide, herbicide, or fertilizer.

Construction triggers added paperwork under subsection I.8: a project disturbing five acres or more, including a lot that is part of a larger common plan of development, needs both a Notice of Intent and a Stormwater Pollution Prevention Plan (SWPPP) to satisfy LDEQ, while a project of one acre up to five acres needs a SWPPP but not a Notice of Intent. Subsection G requires a signed stormwater agreement for any project needing a building permit, site work permit, or subdivision work order, committing the owner to get any needed LDEQ permit and follow state, federal, and local rules for the life of the project. Developments of five acres or more also get modeled for water quality impacts under subsection K, and cannot reduce dissolved oxygen in a receiving stream by more than 0.2 mg/L. Anyone can file a stormwater complaint with the MS4 Administrator, verbally or in writing, and the parish keeps a written record on file for three years under subsection M.