Johnston County, NC Environmental Rules: Stormwater Management (2026)

Johnston County's stormwater quantity standard sits in the Land Development Code's stormwater management article, administered by the county stormwater administrator. Section 14-387 requires runoff to be conveyed through a designed drainage system of natural drainageways, grass swales, storm sewers, culverts, inlets and channels that encourages infiltration and controls velocity and flooding. The attenuation standard is tiered by location: in the Environmentally Sensitive (ES) area district and the Middle Creek Watershed, a development's post-construction peak runoff must be held at or below the pre-development rate for every storm from the one-year event through the 100-year event; everywhere else in the county's planning jurisdiction, the same test applies for the one-year through 25-year event.

Section 14-387(b)(3) exempts single-family and duplex projects of 19 lots or fewer that raise peak runoff by no more than 8 percent, and commercial or industrial projects adding less than 10,000 square feet of built-upon area within an existing permit's threshold, unless the stormwater administrator finds a downstream impact risk. 6 pounds per acre per year under § 14-388. 00 per day, with each day of continuing violation a separate offense. Enforcement decisions and permit denials can be appealed in writing to the county Board of Adjustment within 15 days under § 14-400.