S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.C
(1) Site/Permitting Requirements
(a) There must not be a zone of saturation (ZOS) within twenty-four (24) inches of the naturally occurring soil surface.
(b) The depth to any restrictive horizon must be greater than twelve (12) inches below the bottom of the proposed wastewater infiltration trenches.
(c) The texture in the upper eighteen (18) inches of naturally occurring soil may either be Class I, Class II, Class III, or Class IV.
(d) The long-term acceptance rate for system sizing shall be based upon 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.
(e) Due to the decreased sidewall absorption area and the increased potential for ground water mounding near the surface, the Equivalency Factors for these systems shall be calculated by conventional wastewater infiltration trenches and increased by an additional factor of 0.09 times.
(f) 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.
(g) This system must not be used on sloping sites that require serial distribution unless it can be demonstrated that the entire wastewater infiltration trench installation (i.e., side wall to side wall and end to end) can meet the required textural limitations and the required offsets to the zone of saturation and restrictive horizons.
(h) This system cannot be considered for facilities with peak flow rates in excess of fifteen hundred (1500) gpd.
(2) Installation Requirements
(a) The wastewater infiltration trench aggregate shall be nine (9) inches in depth and shall be covered with at least nine (9) inches of backfill.
(b) The wastewater infiltration trench width shall be thirty-six (36) inches.
(c) The maximum depth of the bottom of the wastewater infiltration trench shall be eighteen (18) inches below the naturally occurring soil surface unless it can be demonstrated that deeper placement can meet the required textural limitations and the offsets to the zone of saturation and restrictive horizons.
(d) 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).
(e) All tree and brush removal shall be done in a manner that minimizes the disturbance or loss of naturally occurring soil.
(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 to a positive outfall. The septic tank and subsurface wastewater infiltration area shall be backfilled and shaped to promote surface water runoff.
(b) A barrier to preclude parking and vehicular traffic over the system area may be required.
(c) Following final landscaping, seeding or sodding may be required to prevent erosion.
(d) 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.C