North Carolina Administrative Code › Title 15A - Environmental Quality › Chapter 18 - ENVIRONMENTAL HEALTH › Subchapter A - SANITATION › Section .1900 - SEWAGE TREATMENT AND DISPOSAL SYSTEMS › Section 18A .1955 - DESIGN INSTALLATION CRITERIA FOR CONVENTIONAL SEWAGE SYSTEMS

Current through Register Vol. 39, No. 2, July 15, 2024
(a) Conventional septic tank systems shall
				  utilize a septic tank of approved construction with an approved effluent filter
				  and support case, access devices, and design volume which provides primary
				  treatment of the sewage in accordance with the provisions of these Rules. The
				  effluent filter support case shall be solvent welded to a PVC Schedule 40
				  outlet pipe with a minimum diameter of three inches inserted through the outlet
				  connective sleeve creating a watertight and mechanically sound joint and shall
				  extend at least 24 inches beyond the tank outlet. The filter and support case
				  shall be installed and maintained in accordance with the filter manufacturer's
				  specifications. The effluent filter shall be accessible without the operator
				  entering the septic tank and removable by hand. The effluent filter shall be
				  secured in the support case and located under the outlet access opening or
				  manhole. When the top of the septic tank or access manhole is installed below
				  finished grade, the location of each access opening or manhole shall be visibly
				  marked at finished grade. The visible marker(s) shall be located over or within
				  a five foot radius of each access opening or manhole. The marker(s) shall be
				  identified as a septic tank locator. When not placed over each access opening
				  or manhole, the marker(s) shall indicate location of tank access opening(s) or
				  manhole(s). The filtered effluent from the septic tank shall be conveyed to an
				  approved nitrification line where the soil provides for final treatment and
				  disposal of the sewage.
(b) Table
				  II shall be used in determining the maximum long-term acceptance rate for
				  septic tank systems of conventional trench design. The long-term acceptance
				  rate shall be based on the most hydraulically limiting naturally occurring soil
				  horizon within three feet of the ground surface or to a depth of one foot below
				  trench bottom, whichever is deeper.
TABLE II
LONG-TERM
SOIL GROUP
SOIL TEXTURE CLASSES
(USDA CLASSIFICATION)
ACCEPTANCE RATE
gpd/ft2
I
Sands
(With S or PS structure and clay
								mineralogy)
Sand
Loamy Sand
1.2 - 0.8
II
Coarse Loams
(With S or PS structure and clay
								mineralogy)
Sand
Loamy Sand
0.8 - 0.6
III
Fine Loams
(With S or PS structure and clay
								mineralogy)
Sandy Clay
Loam
Silt Loam
Clay Loam Silty Clay Loam
Silt
0.6 - 0.3
IV
Clays
(With S or PS structure and clay
								mineralogy)
Sandy Clay
Silty Clay
Clay
0.4 - 0.1
The long-term acceptance rate shall not exceed the mean
					 rate for the applicable soil group for food service facilities, meat markets,
					 and other places of business where accumulation of grease can cause premature
					 failure of a soil absorption system. Long-term acceptance rates up to the
					 maximum for the applicable soil group may be permitted for facilities where
					 data from comparable facilities indicates that the grease and oil content of
					 the effluent will be less than 30 mg/l and the chemical oxygen demand (COD)
					 will be less than 500 mg/l.
(c) The design daily sewage flow shall be
				  divided by the long-term acceptance rate to determine the minimum area of
				  nitrification trench bottom. The total length of the nitrification line shall
				  be determined by dividing the required area of nitrification trench bottom by
				  the trench width, not to exceed 36 inches. Trenches shall be located not less
				  than three times the trench width on centers with a minimum spacing of five
				  feet on centers.
(d) The local
				  health department may permit the use of a bed system on sites where the soil
				  texture can be classified into either Soil Groups I, II, or III, meeting the
				  other requirements of this Section, and only on lots which are limited by
				  topography, space, or other site-planning considerations. In such cases, the
				  number of square feet of bottom area needed shall be increased by 50 percent
				  over what would be required for a trench system. Nitrification lines shall be
				  at least 18 inches from the side of the bed and shall have lines on three-foot
				  centers. When the design daily flow exceeds 600 gallons per day, bed systems
				  shall not be used.
(e) The pipe or
				  tubing used between the septic tank and the nitrification line shall be a
				  minimum of three-inch nominal size Schedule 40 polyvinyl chloride (PVC),
				  polyethylene (PE), or acrylonitrile-butadiene-styrene (ABS) or equivalent with
				  a minimum fall of one-eighth inch per foot. However, three-inch or greater
				  nonperforated polyethylene (PE) corrugated tubing may be substituted for
				  Schedule 40 pipe between a distribution device and the nitrification line if
				  the following conditions are met:
(1) the
				  trench has a minimum bottom width of one foot;
(2) the trench bed is compacted, smooth, and
				  at a uniform grade;
(3) the pipe is
				  placed in the middle of the trench with a minimum of three inches of clearance
				  between the pipe and the trench walls;
(4) washed stone or washed gravel envelope is
				  placed in the trench on both sides of the pipe and up to a point at least two
				  inches above the top of the pipe;
(5) a minimum of six inches of soil cover is
				  placed and compacted over the stone or gravel envelope; and
(6) earthen dams consisting of two feet of
				  undisturbed or compacted soil are placed at both ends of the trench separating
				  the trench from the distribution device and the nitrification line.
All joints from the septic tank to the nitrification line
					 shall be watertight.