North Carolina Administrative Code › Title 15A - Environmental Quality › Chapter 18 - ENVIRONMENTAL HEALTH › Subchapter A - SANITATION › Section .1900 - SEWAGE TREATMENT AND DISPOSAL SYSTEMS › Section 18A .1952 - SEPTIC TANK, EFFLUENT FILTER, DOSING TANK AND LIFT STATION DESIGN

Current through Register Vol. 39, No. 2, July 15, 2024
(a) A septic tank or dosing tank shall be
				  watertight, structurally sound, and not subject to excessive corrosion or
				  decay. Septic tanks shall be of two-compartment design. The inlet compartment
				  of a two-compartment tank shall hold between two-thirds and three-fourths of
				  the total tank capacity. Septic tanks shall have an approved effluent filter
				  and access devices. The effluent filter shall function without a bypass of
				  unfiltered wastewater, sludge or scum. The effluent filter case shall be
				  designed to function as a sanitary tee with the inlet extending down to between
				  25 and 40 percent of the liquid depth. The requirement(s) for an effluent
				  filter and access devices shall apply to septic tanks for which a Construction
				  Authorization is issued on or after January 1, 1999. A properly designed dosing
				  siphon or pump shall be used for discharging sewage effluent into nitrification
				  lines when the total length of such lines exceeds 750 linear feet in a single
				  system and as required for any pressure-dosed system. When the design daily
				  flow from a single system exceeds 3,000 gallons per day or when the total
				  length of nitrification lines exceeds 2,000 linear feet in a single system,
				  alternating siphons or pumps shall be used which shall discharge to separate
				  nitrification fields. The dose volume from pump or siphon systems shall be of
				  such design so as to fill the nitrification lines from 66 percent to 75 percent
				  of their capacity at each discharge except as required for low-pressure
				  distribution systems. The discharge rate from dosing systems shall be designed
				  to maximize the distribution of the effluent throughout the nitrification
				  field. Septic tanks installed where the top will be deeper than six inches
				  below the finished grade shall have an access manhole over each compartment
				  with cover, extending to within six inches of the finished grade, having a
				  minimum opening adequate to accommodate the installation or removal of the
				  septic tank lid, septage removal, and maintenance of the effluent filter. When
				  the top of the septic tank or access manhole is below the finished grade, the
				  location of each manhole shall be visibly marked at finished grade. Any system
				  serving a design unit with a design sewage flow greater than 3,000 gallons per
				  day shall have access manholes that extend at least to finished grade and be
				  designed and maintained to prevent surface water inflow. The manholes shall be
				  sized to allow proper inspection and maintenance. All dosing tanks shall have a
				  properly functioning high-water alarm. The alarm shall be audible and visible
				  by system users and weatherproof if installed outdoors. The alarm circuit shall
				  be provided with a manual disconnect in a watertight, corrosion-resistant
				  outside enclosure (NEMA 4X or equivalent) adjacent to the dosing
				  tank.
(b) Minimum liquid capacities
				  for septic tanks shall be in accordance with the following:
(1) Residential Septic Tanks (for each
				  individual residence or dwelling unit):
Number of Bedrooms
Minimum Liquid Capacity
Equivalent Capacity Per Bedroom
3 or less
900 gallons
300 gallons
4
1,000 gallons
250 gallons
5
1,250 gallons
250 gallons
(2) Septic tanks for large residences,
				  multiple dwelling units, or places of business or public assembly shall be in
				  accordance with the following:
(A) The liquid
				  capacity of septic tanks for places of business or places of public assembly
				  with a design sewage flow of 600 gallons per day or less shall be determined in
				  accordance with the following: V = 2Q; where V is the liquid capacity of the
				  septic tank and Q is the design daily sewage flow. However, the minimum
				  capacity of any septic tanks shall be 750 gallons.
(B) Individual residences with more than five
				  bedrooms, multiple-family residences, individual septic tank systems serving
				  two or more residences, or any place of business or public assembly where the
				  design sewage flow is greater than 600 gallons per day, but less than 1,500
				  gallons per day, the liquid capacity of the septic tank shall be designed in
				  accordance with the following: V = 1.17Q + 500; where V is the liquid capacity
				  of the septic tank and Q is the design daily sewage flow. The minimum liquid
				  capacity of a septic tank serving two or more residences shall be 1,500
				  gallons.
(C) Where the design
				  sewage flow is between 1,500 gallons per day and 4,500 gallons per day, the
				  liquid capacity of the septic tank shall be designed in accordance with the
				  following: V = 0.75Q + 1,125; where V is the liquid capacity of the septic tank
				  and Q is the design daily sewage flow.
(D) Where the design sewage flow exceeds
				  4,500 gallons per day, the septic tank shall be designed in accordance with the
				  following: V = Q; where V is the liquid capacity of the septic tank and Q is
				  the design daily sewage flow.
(E)
				  The minimum liquid capacity requirements of Subparagraph (b)(2) of this Rule
				  shall be met by use of a single two-compartment septic tank or by two tanks
				  installed in series, provided the first tank is constructed without a baffle
				  wall and contains at least two-thirds of the total required liquid
				  capacity.