North Carolina Administrative Code
Title 15A - Environmental Quality
Chapter 02 - ENVIRONMENTAL MANAGEMENT
Subchapter B - SURFACE WATER AND WETLAND STANDARDS
Section .0200 - CLASSIFICATIONS AND WATER QUALITY STANDARDS APPLICABLE TO SURFACE WATERS AND WETLANDS OF NORTH CAROLINA
Section 02B .0224 - WATER QUALITY STANDARDS FOR HIGH QUALITY WATERS

(A) rated excellent based on biological and physical/chemical characteristics through monitoring or special studies; or

(B) primary nursery areas (PNA) and other functional nursery areas designated by the Marine Fisheries Commission or the Wildlife Resources Commission.

(A) Oxygen Consuming Wastes: Effluent limitations for oxygen consuming wastes shall be BOD5= 5 mg/l, NH3-N = 2 mg/l, and DO = 6 mg/l. More stringent limitations shall be set, if necessary, to ensure that the cumulative pollutant discharge of oxygen-consuming wastes does not cause the DO of the receiving water to drop more than 0.5 mg/l below background levels, and in no case below the standard. Where background information is not available, evaluations shall assume a percent saturation determined by staff to be applicable to that hydroenvironment.

(B) Total Suspended Solids: Discharges of total suspended solids (TSS) shall be limited to effluent concentrations of 10 mg/l for trout waters and HQW-classified PNAs and 20 mg/l for all other High Quality Waters.

(C) Disinfection: Alternative methods to chlorination shall be required for discharges to trout streams, except that single family residences may use chlorination if other options are not economically feasible, as determined on a case-by-case basis. Domestic discharges to SA waters shall be prohibited.

(D) Emergency Requirements: Reliable treatment designs shall be employed, such as stand-by power capability for entire treatment works, dual train design for all treatment components, or other reliable treatment designs in accordance with 15A NCAC 02H .0124.

(E) Volume: The total volume of treated wastewater for all discharges combined shall not exceed 50 percent of the total instream flow under 7Q10 conditions.

(F) Nutrients: Where nutrient overenrichment is projected to be a concern, effluent limitations shall be set for phosphorus or nitrogen, or both.

(G) Toxic substances: In cases where complex wastes (those containing or potentially containing toxicants) may be present in a discharge, a safety factor shall be applied to any chemical or whole effluent toxicity allocation. The limit for a specific chemical constituent shall be allocated at one-half of the normal standard at design conditions. Whole effluent toxicity shall be allocated to protect for chronic toxicity at an effluent concentration equal to twice that which is acceptable under design conditions. In all instances there may be no acute toxicity in an effluent concentration of 90 percent. Ammonia toxicity shall be evaluated according to EPA guidelines promulgated in "Ambient Water Quality Criteria for Ammonia - 1984"; EPA document number 440/5-85-001; NITS number PB85-227114; July 29, 1985 (50 FR 30784) or "Ambient Water Quality Criteria for Ammonia (Saltwater) - 1989"; EPA document number 440/5-88-004; NTIS number PB89-169825. This material related to ammonia toxicity is available at no cost at https://www.epa.gov/wqc/aquatic-life-criteria-ammonia and https://www.epa.gov/sites/production/files/2019-02/documents/ambient-wqc-ammonia-saltwater-1989.pdf, and is hereby incorporated by reference including subsequent amendments and editions.