14 CAR § 21-702. Trench depths

(a) Soil absorption areas utilizing pipe and gravel provide for a trench twenty-four inches (24”) wide, with a standard trench depth of eighteen inches (18”) from the bottom of the trench to the finished settled grade. (b) Systems designed with trench depths up to twenty-four inches (24”) may be utilized. (c)(1) There shall be a minimum of: (A) Six inches (6”) of gravel below the pipe; and (B) Two inches (2”) of gravel above the pipe. (2) A minimum of six inches (6”) of cover is required above the gravel bed or gravel substitute. (d)(1) The trench depth may vary in those instances where the soil absorption area was designed to overcome limiting soil characteristics. (2) Trench depths shall be: (A) Specifically called for in the designated representative’s design; and (B) Approved by the authorized agent. (e) The absorption area in square feet is twice the total length of the trenches. (f) The minimum spacing between the trenches shall be six feet (6’) between the trenches and eight feet (8’) center to center. (g) Increased separation between trenches is encouraged to enhance the effectiveness of the trenching system.