North Carolina Septic Tank Installation Regulations

By Duane Craig - Updated June 13, 2017
Septic pump truck

North Carolina has very specific requirements for septic tank installation. Septic systems in that state must be designed to fit the soil conditions of the site and the surrounding area. Septic tanks are one part of an on site sewage disposal system that is used by single family residences across the state where municipal or community sewage disposal is not available.

Definition

North Carolina defines a septic tank as a "water-tight, covered receptacle designed for primary treatment of sewage,” that will get sewage from a building, separate floating waste from sinking waste, use anaerobic action to digest organic waste, store solids, and let the liquids flow out for further treatment and disposal.

Setbacks

Septic tanks must be at least 100 feet away from private or public water supplies, streams, and reservoirs. Keep them at least 50 feet away from coastal waters, canals, marshes, storm water retention ponds, lakes, and ponds. Maintain 15 feet between septic tanks and basements, embankments, drainage system side-slopes, and swimming pools. Septic tanks also must be at least 10 feet away from property lines, water lines, and the up-slope portion of drainage systems. There is also a setback of 25 feet for groundwater lowering ditches and devices, and the down-slope of drainage systems. Septic tanks cannot be placed where there may be flooding every 10 years or less, unless they are watertight and can stay watertight during a storm.

Installation Specifications

The state requires septic tanks to have two compartments with an inlet compartment able to hold between 2/3 and 3/4 of the tank’s total capacity. Use an effluent filter and maintain access to the filter and the tank. Use a sanitary tee on the inlet and outlet. Install a manhole and cover on each tank access point when the top of the tank is lower than 6 inches from ground surface. Mark each manhole location if the cover is below grade. A home with three bedrooms or fewer requires at least a 900 gallon tank. Four bedrooms requires at least a 1,000 gallon tank, and five bedrooms requires at least a 1,250 gallon tank.

Solvent weld the effluent filter support case to a 3-inch minimum diameter PVC schedule 40 pipe. This support case should be at least 24 inches from the septic tank outlet and must be watertight. The outlet line from the septic tank must carry the effluent to an approved nitrification line (leach field) for final treatment.

Regulating authorities approve prefabricated septic tanks based on the septic system plans and the specifications of the tank.

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