Simpsonville, SC Environmental Rules: Stormwater Management (2026)

Greenville County operates a regulated Municipal Separate Storm Sewer System (MS4) under the federal Clean Water Act's NPDES Phase II program (40 CFR Part 122) because portions of the unincorporated county lie within a U.S. Census Bureau Urbanized Area. In South Carolina, EPA has delegated NPDES permitting authority to the state; permits for MS4s, industrial stormwater, and construction stormwater are now issued by the South Carolina Department of Environmental Services (SCDES), which took over the environmental functions of the former SC Department of Health and Environmental Control (SC DHEC) under the 2023–2024 state reorganization (the public-health functions went to the new SC Department of Public Health, SCDPH).

Greenville County's coverage as an MS4 is implemented locally through the Greenville County Storm Water Management Ordinance, administered by the Land Development Division. The ordinance's stated purpose is to control the adverse effects of increased stormwater runoff from future development and existing developed land, reduce property damage and flooding, and maintain water-quality standards in receiving streams. To do that, the ordinance requires that new development and redevelopment in unincorporated Greenville County submit stormwater management plans that address runoff rate and volume, water-quality treatment, channel protection, and soil erosion / sediment control (SESC) during construction.

Erosion and sediment control plan review and inspection — including review of the South Carolina NPDES Construction General Permit (CGP) Stormwater Pollution Prevention Plan (SWPPP) for sites that disturb one acre or more (or less than one acre if part of a larger common plan of development) — is delegated under a Memorandum of Agreement to the Greenville County Soil & Water Conservation District, which is the local implementing agency. The District reviews plans, conducts site inspections, and recommends enforcement actions back to SCDES when violations are observed.

The ordinance also implements the federal NPDES Phase II Illicit Discharge Detection and Elimination (IDDE) minimum control measure: non-stormwater discharges (any discharge to the storm sewer that is not composed entirely of stormwater) are prohibited, except for certain categorical allowable non-stormwater flows such as landscape irrigation, uncontaminated groundwater, firefighting flows, and other discharges expressly listed in the NPDES Phase II rule. Examples of prohibited illicit discharges include motor-vehicle fluids (oil, gasoline, antifreeze, transmission fluid), commercial car-wash wastewater that runs off-site, paint, sanitary sewage, septic-tank pumpings, swimming-pool dechlorinated water that is contaminated, industrial process wastewater, grass clippings or leaf litter blown or swept into the drain, and pet waste deliberately swept into the drain.