S.D. Admin. R. 74:53:01:23

Current through Register Vol. 51, page 67, December 16, 2024

Section 74:53:01:23 - Design and construction requirements for septic tanks

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.

S.D. Admin. R. 74:53:01:23

12 SDR 2, effective 7/18/1985; 13 SDR 129, 13 SDR 141, effective 7/1/1987; transferred from

General Authority: SDCL 34A-2-93.

Law Implemented: SDCL 34A-2-20.