Charleston County, SC Stormwater Regulations

Charleston County holds a Phase II Small MS4 NPDES permit and manages stormwater through its county stormwater utility. Tidal flooding and sea level rise create persistent challenges for stormwater infrastructure. SCDES enforces state penalties up to $10,000 per day, and the county enforces local stormwater ordinances with additional fines.

Primary source: South Carolina Department of Environmental Services (SCDES)

Permit Requirements

Charleston County requires NPDES Construction General Permit (SCR100000) coverage from SCDES for any land disturbance of one acre or more. The City of Charleston and other municipalities within the county may have additional local permitting requirements that apply to smaller projects.

OCRM coastal zone permits are required for projects within the tidal critical area, which covers significant portions of Charleston County. This includes most barrier islands, tidal creek buffers, and marsh-adjacent properties. The dual permitting process, requiring both SCDES and OCRM approval, adds time and complexity to project timelines.

Charleston County's stormwater division reviews development plans for compliance with the MS4 permit and local ordinances. Post-construction stormwater management plans must demonstrate that permanent BMPs will treat runoff from impervious surfaces and manage peak discharge rates.

Inspection Obligations

Active construction sites must be inspected weekly and within 24 hours of rainfall events producing 0.5 inches or more. Charleston County conducts its own construction site inspections in addition to the self-inspection requirements under the NPDES permit.

Permanent stormwater BMPs require annual inspections by the responsible party. Charleston County maintains an inventory of permitted stormwater facilities and periodically inspects them for compliance. Properties with maintenance agreements on file must demonstrate ongoing maintenance through inspection documentation.

The county's illicit discharge detection and elimination (IDDE) program involves dry-weather screening of outfalls throughout the MS4 area. Staff investigate reports of unusual discharges, staining, odors, or other indicators of non-stormwater flows entering the drainage system.

Penalty Structure

State penalties under the SC Pollution Control Act reach $10,000 per day per violation. SCDES can issue administrative orders, assess penalties, require stop-work, and mandate corrective action. Violations involving unpermitted discharges to tidal waters or coastal critical areas can trigger OCRM enforcement actions in addition to SCDES penalties.

Charleston County enforces its local stormwater ordinance through notices of violation, compliance orders, and fines. The county has authority to perform emergency repairs on failing stormwater systems and recover costs from property owners. Repeated violations can result in referral to SCDES for state-level enforcement.

The City of Charleston has its own stormwater enforcement mechanisms, separate from the county. Properties within the city limits may face enforcement from both the city and SCDES, depending on the nature of the violation.

Key BMPs

Charleston County's extremely flat topography, high water table, and tidal influence limit BMP options compared to inland areas. Effective BMPs for the Charleston area include:

• Wet detention ponds - The primary BMP for most developments. Must account for tidal backwater effects on outlet structures and may require tide gates on outfalls.
• Bioretention with underdrains - Essential for areas with high water tables. Standard bioretention designs must be modified with underdrain systems to function in Charleston's saturated soils.
• Constructed wetlands - Well-suited to the local hydrology. Provide water quality treatment while mimicking natural marsh systems common throughout the county.
• Permeable pavement - Increasingly popular for parking areas and low-traffic surfaces. Requires careful design due to high groundwater and tidal influence.
• Tide gates and pump stations - Critical infrastructure for managing tidal flooding impacts on stormwater systems. The county has invested in these systems at key outfall locations.

Local Ordinances

Charleston County's stormwater management ordinance implements the requirements of its MS4 permit and addresses local drainage concerns. The ordinance covers construction site runoff controls, post-construction stormwater management, illicit discharge prohibition, and maintenance requirements for permanent BMPs.

The county operates a stormwater utility funded by fees assessed on developed properties based on impervious surface area. These fees support drainage maintenance, flood mitigation, water quality monitoring, and MS4 permit compliance activities.

Sea level rise adaptation is an increasing focus of Charleston County's stormwater planning. The county's comprehensive plan incorporates sea level rise projections into infrastructure design standards, and new stormwater systems must consider future tidal conditions.