Dorchester County, SC Stormwater Regulations

Dorchester County holds a Phase II Small MS4 NPDES permit as part of the greater Charleston urbanized area. The county enforces stormwater management for construction and post-construction activities, with rapid residential growth around Summerville driving increased permit activity. State penalties reach $10,000 per day for violations.

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

Permit Requirements

Dorchester County requires NPDES Construction General Permit (SCR100000) coverage for land disturbance of one acre or more. The county reviews stormwater management plans as part of its development review process and requires developers to demonstrate adequate stormwater management before construction begins.

As part of the Charleston metro MS4, Dorchester County must ensure that post-construction stormwater controls meet the performance standards outlined in its NPDES permit. New development and redevelopment projects within the MS4 urbanized area must incorporate permanent BMPs designed to treat stormwater runoff and manage peak flows.

Summerville's rapid growth has made Dorchester County one of the most active construction markets in the Charleston metro area. The volume of new residential subdivisions, commercial projects, and infrastructure improvements along the I-26 and US-17A corridors generates significant stormwater permitting activity.

Inspection Obligations

Construction sites must be inspected at least weekly and within 24 hours of rainfall events producing 0.5 inches or more. Inspectors verify that erosion and sediment controls are installed correctly, maintained properly, and functioning as designed. Inspection records must be maintained on site or available for review.

Post-construction BMPs require annual inspections by the property owner or responsible party. Dorchester County tracks permitted facilities and may inspect them for compliance. HOAs that inherit stormwater ponds and detention basins from developers must maintain these facilities and keep inspection records.

The county's IDDE program includes dry-weather screening of storm sewer outfalls and investigation of reported illicit discharges. Dorchester County staff conduct field inspections to identify non-stormwater flows and trace them back to their source.

Penalty Structure

SCDES enforces stormwater violations at the state level, with civil penalties up to $10,000 per day per violation under the SC Pollution Control Act. State enforcement actions include administrative orders, stop-work orders, and permit revocation.

Dorchester County enforces its local stormwater ordinance through notices of violation, compliance deadlines, and fines. The county can require property owners to repair or replace failing BMPs and can perform emergency maintenance if the owner fails to act, recovering costs through liens or direct billing.

Given the high volume of construction activity in the county, SCDES and county inspectors actively monitor development sites for compliance. Developers with repeated violations may face increased inspection scrutiny and escalated enforcement.

Key BMPs

Dorchester County's inland location and varied terrain, from low-lying areas near the Ashley River to uplands near Summerville, support a range of BMP types:

• Wet detention ponds - Standard for residential subdivisions throughout the county. Must maintain permanent pool volume and treat the first inch of runoff.
• Dry detention basins - Used where permanent pools aren't practical. Provide peak flow attenuation and must drain within 72 hours.
• Bioretention systems - Increasingly common in newer commercial and residential developments. Engineered soil media provides water quality treatment before discharge.
• Level spreaders - Used to convert concentrated stormwater flows to sheet flow before discharge to vegetated areas. Common along the edges of developed parcels.
• Grass channels - Used for conveyance and treatment along roadways in residential developments. Require regular mowing and debris removal.

Local Ordinances

Dorchester County's stormwater management ordinance implements the six minimum control measures required under its MS4 permit. The ordinance covers public education and outreach, illicit discharge prohibition, construction site runoff control, post-construction stormwater management, and pollution prevention for county operations.

The county requires maintenance agreements for all permanent stormwater BMPs constructed as part of new development. These agreements run with the land and obligate current and future property owners to maintain facilities in proper working condition. The agreement specifies the county's right to inspect and enforce maintenance requirements.

The Town of Summerville has its own stormwater regulations that may apply within its municipal limits, in addition to county and state requirements. Projects within Summerville should verify local requirements with the town's planning department.