S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.M
(1) Site/Permitting Requirements
(a) Use of the double aggregate depth option must be restricted to soils that meet all textural limitations and required offsets to the zone of saturation (ZOS) and restrictive horizons.
(b) Systems incorporating the double aggregate depth option shall be loaded on the basis of the most hydraulically limiting naturally occurring soil texture from the ground surface to twelve (12) inches below the bottom of the proposed wastewater infiltration trenches.
(c) In order to maintain the same total absorptive area as that provided by conventional aggregate depth systems, the equivalent linear footage requirement for thirty-six (36) inch wide double aggregate depth trenches shall be determined by multiplying the conventional trench requirement by a factor of 0.7.
(d) There shall be a replacement area equivalent to at least fifty (50) percent in size of the original system area held in reserve for system repair. This area shall have a suitable configuration and shall meet the minimum soil and site conditions of this regulation.
(2) Installation Requirements
(a) The wastewater infiltration trench aggregate shall be twenty-eight (28) inches in depth and shall be placed so as to provide twenty (20) inches of aggregate below the pipe, five (5) inches beside the pipe, and three (3) inches above the pipe. The aggregate shall be covered with at least nine (9) inches of backfill.
(b) The wastewater infiltration trench width shall be thirty-six (36) inches.
(c) Where gravity flow from the septic tank to the subsurface wastewater infiltration area is utilized, the invert elevation of the septic tank outlet shall be installed at an elevation at least equal to or higher than the top of the aggregate in the highest wastewater infiltration trench(es).
(3) Final Landscaping and Drainage
(a) Installation of drainage swales, ditches, curtain drains, and rain gutters may be required to divert or intercept water away from the onsite wastewater system location. The septic tank and subsurface wastewater infiltration area shall be backfilled and shaped to promote surface water runoff.
(b) Following final landscaping, seeding or sodding may be required to prevent erosion.
(c) Final approval shall be withheld until all landscaping and drainage improvements have been satisfactorily completed.
S.C. Code Regs. ch. 61, 61-56, 61-56.400, app 61-56.400.M