13.20.530 Requirements for absorption beds.
Absorption beds may not be constructed where the soil percolation rate is 30 or more minutes per inch. An absorption bed may be designed and constructed for gravity or pressure flows in accordance with the following criteria:
A. A gravity absorption bed system shall consist of a level bed not exceeding 100 feet in length, 15 feet in width, and 3 feet in depth. Each distribution line shall extend the length of the bed, and shall be spaced not greater than 5 feet on center across the bed width. The distribution lines shall be preceded by a distribution box, to provide uniform distribution of effluent. The outermost distribution lines may not be closer than 30 inches to the bed walls, and all ends shall be capped if it is not a closed-loop system;
B. A pressurized absorption bed system may exceed the length and width requirements in ARSD subdivision 74:53:01:36 (1), but must not be more than 3 feet in depth. The bed bottom shall be level. Each distribution line shall be installed within the perimeter limits of the bed, and spaced not greater than 10 feet on center across the bed. The bed shall be center-fed by a manifold pipe. The outermost distribution lines may not be closer than 5 feet to the bed wall perimeter. The distribution system shall be closed-loop or have all ends capped; and
C. Additional requirements for gravity and pressurized absorption bed systems are as follows:
1. The distribution pipe network shall meet the requirements of ARSD subdivision 74:53:01:37 (8);
2. The distribution lines shall be placed in at least a 12-inch layer of 1/2-inch- to 1-1/2-inch-diameter washed gravel, with at least 6 inches of gravel beneath, and 2 inches of gravel above each line; and
3. The gravel above the distribution line shall be covered with untreated building paper, then a 6-inch layer of loose marsh hay or straw, and then a top layer of 12 inches of soil over the entire bed. Flax straw may not be used.
D. (Note: Parallel beds must be at least 10 feet apart. See also § 13.20.540G.)