9.4 Erosion & Sediment Control: The Sedimentation Pollution Control Act & 15A NCAC 04

9.4 Erosion & Sediment Control: The Sedimentation Pollution Control Act & 15A NCAC 04

The Board's exam description says the state-specific exam tests the incidental drainage guidelines "with respect to erosion control and surface drainage," and the reference list names the NCDEQ Erosion and Sediment Control Planning and Design Manual. This is squarely inside the 16 percent Drainage weight.

The governing law is the Sedimentation Pollution Control Act of 1973, Article 4 of G.S. Chapter 113A, implemented by the Sedimentation Control Commission through Title 15A, Chapter 04 of the Administrative Code, and administered by the Division of Energy, Mineral, and Land Resources or by a delegated local program.

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1. The Five Mandatory Standards — G.S. 113A-57

"No land-disturbing activity subject to this Article shall be undertaken except in accordance with the following mandatory requirements":

[!IMPORTANT] The trigger is more than one acre, not "one acre or more." A tract disturbing exactly one acre does not cross the statutory threshold, though a delegated local ordinance may set a stricter one — many North Carolina municipalities do, some as low as one-half acre. Always check the local program.

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2. Plan Review Timelines — G.S. 113A-54.1

Additional provisions worth knowing: a draft plan must contain the applicant's address, and a non-resident applicant must designate a North Carolina agent for notice. Where the applicant is not the landowner, the plan must include the owner's written consent — except that for utility-line construction for water, sewer, gas, telecommunications, or electrical service, the plan may be submitted without written consent so long as the owner received prior notice. A disapproval must state in writing the specific reasons. The Commission shall disapprove a plan whose implementation would violate riparian buffer rules adopted by the Environmental Management Commission. The Director may also disapprove where the applicant or an affiliate is conducting or has conducted land-disturbing activity without an approved plan, has an uncured notice of violation, has failed to pay a civil penalty when due, or has been convicted under G.S. 113A-64(b).

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3. Ground Cover Deadlines — 15A NCAC 04B .0107

The statute says 21 days. The rule, readopted effective April 1, 2020, is considerably tighter, and it is the rule that gets enforced.

+-----------------------------------------------------------------------------+
|            15A NCAC 04B .0107 - GROUND COVER TIMEFRAMES                     |
|                                                                             |
|  GRADING COMPLETED on an area:                                              |
|      Temporary or permanent ground cover sufficient to restrain erosion     |
|      as soon as practicable, but NOT LATER THAN 7 DAYS after completion     |
|      of grading.                                                            |
|                                                                             |
|  GRADING NOT COMPLETED - temporary ground cover required if the area has    |
|  not been disturbed for:                                                    |
|      No slope ............................................. 14 DAYS         |
|      Moderate slope (3:1 or flatter) ...................... 10 DAYS         |
|      Steep slope (steeper than 3:1) ....................... 7 DAYS          |
+-----------------------------------------------------------------------------+

The rule defines its own terms: a moderate slope is an inclined area whose inclination is less than or equal to three units horizontal to one unit vertical; a steep slope is one greater than three horizontal to one vertical.

[!CAUTION] A separate 7-day and 14-day table circulates widely and is often labeled ".0107." It belongs to the NCG01 Construction General Permit, the NPDES stormwater permit for construction activity, whose ground stabilization table distinguishes perimeter dikes, swales, ditches and perimeter slopes (7 days), HQW zones (7 days), slopes steeper than 3:1 (7 days), slopes 3:1 to 4:1 (14 days), and areas flatter than 4:1 (14 days), with a 10-day rule in the Falls Lake watershed. Rule .0107 itself acknowledges that NCG01 requirements "may differ" and places responsibility for complying with NCG01 on the person conducting the activity. On the exam, if the question cites the rule, use 7 / 10 / 14; if it cites the permit, use the permit table.

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4. Design and Performance Standards — 15A NCAC 04B .0108 and Related Rules

The design storm. "Except where otherwise specified in this Chapter, erosion and sedimentation control measures, structures, and devices shall be planned, designed, and constructed to provide protection from the runoff of a 10-year storm that produces the maximum peak rate of runoff as calculated according to procedures in the United States [Department of Agriculture publications]." This is the single most quotable numeric standard in the erosion-control rules.

Channel side slopes. Ditches and channels used as control measures shall be designed and constructed with side slopes no steeper than two horizontal to one vertical if vegetative cover is used for stabilization, unless soil conditions permit steeper slopes or the slopes are stabilized with mechanical devices, structural devices, or ditch liners sufficient to restrain accelerated erosion.

Maintenance responsibility. During site development, the person conducting the land-disturbing activity installs and maintains all temporary and permanent measures required by the approved plan or the Act. After site development, the landowner or person in possession or control installs and maintains all permanent measures — except those within a road or street right-of-way or easement accepted for maintenance by a governmental agency.

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5. High Quality Water Zones — 15A NCAC 04B .0124

Where a project drains to a High Quality Water (HQW) zone, the rule tightens substantially. Only the land-disturbing activity within the HQW zone is governed by this rule.

[!NOTE] The 1,800 cubic feet per acre figure is frequently quoted as a universal North Carolina sediment-basin standard. In the rules it appears in .0124(c)(2), the sensitive-watershed rule for basins discharging to HQW zones. It is very widely applied as good practice statewide and is embedded in the NCDEQ design manual details, but if an exam item asks where the rule requires it, the answer is the HQW context.

Paragraph (d) permits the Director, on written request, to allow alternative design or control measures in lieu of (c)(2) through (c)(5) where meeting all of them creates design or operational hardship and the alternatives provide an equal or more effective level of control — expressly including quicker application of ground cover, sediment flocculants, and enhanced ground cover practices.

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6. What the Surveyor Actually Produces

For a subdivision within incidental scope, the erosion and sedimentation control plan a PLS prepares typically comprises:

1. Existing conditions and drainage areas — the survey the PLS already performed.
2. A construction sequence tied to the ground-cover deadlines above.
3. Perimeter measures — silt fence along contours, construction entrances, inlet protection.
4. Sediment traps or basins sized to the applicable storage and surface-area criteria, dewatered by skimmer or surface withdrawal where required.
5. Diversions and slope drains carrying runoff around or down disturbed slopes at non-erosive velocity.
6. Stabilization specifications — seeding schedule, mulch, matting on steep slopes.
7. Maintenance and self-inspection notes reflecting the operator's ongoing duties.

Where any of that requires a dam, a retaining wall, a structurally designed basin outlet, or a pump, exclusions 4, 5, and 11 of the Board Guidelines put it beyond incidental practice, and a professional engineer must seal it.