South Dakota Administrative Rules › Title 74 - Department of Environment And Natural Resources › Article 74:53 - Water supply and treatment systems › Chapter 74:53:01 - Individual and small on-site wastewater systems › Section 74:53:01:23 - Design and construction requirements for septic tanks

Current through Register Vol. 51, page 10, July 15, 2024
The minimum design and construction requirements for septic tanks are
	 as follows:
(1) Septic tanks shall be
  watertight and constructed of durable materials designed to withstand expected
  physical loads. Such tanks shall be capable of supporting a static vertical
  load of at least 1,000 pounds per square foot when bedded and backfilled to the
  top of the tank. The septic tank, including baffles or tees, shall be
  constructed of materials resistant to acid, decay, and corrosion.
  Prefabricated, coated metal tanks shall meet the requirements of the plumbing
  code, § 20:54:03:03. Coated metal tanks are not permitted for wastewater
  systems when the usage will be longer than seven years. Concrete septic tanks
  shall be constructed of portland type II sulfate-resistant cement with a
  minimum strength of 3,000 pounds per square inch. The walls, floors, and covers
  of concrete septic tanks poured on-site shall be at least 3 1/2 inches thick
  with reinforcing bars and welded wire mesh. Fiberglass or plastic septic tanks
  shall have a minimum wall thickness of 1/4-inch. All special reinforced precast
  concrete, concrete block, plastic, or fiberglass septic tanks shall meet the
  minimum static vertical load requirement of 1,000 pounds per square foot when
  bedded and backfilled to the top of the tank. The interior of concrete block
  septic tanks shall be surfaced with two 1/4-inch coats of portland cement-sand
  plaster and shall have mortar joints. Septic tank keyways or construction
  joints shall be made watertight by grouting with cement or corrosion-resistant
  sealants;
(2) Septic tanks larger
  than 3,000 gallon capacity and fabricated as a single unit shall consist of two
  or more compartments, with 1/2 to 2/3 of the tank capacity in the first
  compartment. The minimum dimension of any interior compartment shall be 2 feet.
  Each compartment shall have at least one access hole with a minimum dimension
  of 20 inches located within 6 feet of all walls of the tank. The access holes
  shall extend through the top of the tank to a point within 12 inches but not
  closer than 6 inches below finished grade, and the access hole covers shall be
  covered with at least 6 inches of earth unless the cover is airtight and
  equipped with a hasp and lock, in which case the cover may be shallower or
  above grade. If the access hole to the tank is covered with more than 12 inches
  of earth backfill, the access hole shall be extended to within 6 inches of the
  finished grade;
(3) There shall be
  inspection pipes of at least 4 inches diameter over both the inlet and outlet
  devices. The inspection pipes shall extend through the top of the tank and be
  capped flush or above finished grade with a removable watertight cap or cover.
  A downward projection of the centerline of the inspection pipe shall be
  directly in line with the centerline of the inlet or outlet device. The tank
  inlet and outlet devices shall consist of baffles or sanitary tees;
(4) The minimum dimension or diameter of
  septic tanks shall be 4 feet. The tank shall have a liquid depth of between 30
  inches and 72 inches and shall have a uniform horizontal flow throughout its
  length;
(5) The inlet elevation
  shall be at least 3 inches higher than the outlet elevation of the tank. The
  outlet elevation shall be at least 9 inches beneath the underside of the top of
  the tank or 20 percent of the total liquid depth, whichever is greater. The
  inlet baffle or tee shall penetrate at least 6 inches, but not more than 20
  percent of the total liquid depth below the liquid level in the tank and not
  lower than the outlet baffle or tee. The outlet baffle or tee shall penetrate
  at least 12 inches, but not more than 35 percent of the total liquid depth in
  horizontal cylindrical tanks or 40 percent of the total liquid depth in
  rectangular tanks, below the liquid level in the tank. The inlet and outlet
  baffle or tee devices shall extend above the liquid level at least 8 inches or
  to within approximately 1 inch of the underside of the tank top. At least 1
  inch of vent space shall be provided between the baffle or tee devices and the
  underside of the top of the tank. The separation distance between the inlet or
  outlet opening at the tank wall to the nearest point on baffles or tees shall
  not be less than 6 inches nor more than 12 inches;
(6) When a partition wall is used to form a
  multicompartment tank, the partition wall opening shall be not less than 4
  inches in diameter and not smaller than the diameter of the influent and
  effluent pipes. The opening shall be located at the same elevation as the
  effluent pipe with sanitary tees or baffles having the same size and location
  requirements as for the inlet and outlet devices. The top of the partition
  wall, including baffles or tees, shall be set at least 1 inch below the
  underside of the tank top to provide adequate venting. All partitions, tees,
  and baffles shall be permanently and securely attached to the tank;
  and
(7) The effluent pipe exiting
  the unit shall be at least 6 feet in length and unperforated until the first
  tee, distribution box, or drop box before the absorption field is
  encountered.
General Authority:
SDCL
		34A-2-93.
Law Implemented:
SDCL
		34A-2-20.