S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.H
(1) Site/Permitting Requirements
(a) There must not be a zone of saturation (ZOS) within fifteen (15) 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 must be no more limiting than Class III.
(d) 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.
(e) 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.
(f) 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.
(g) No part of this system can be installed within 125 feet of the critical area line or tidal waters as determined by the Department; or within 125 feet of the ordinary high water elevation within the banks of non-tidal, environmentally sensitive waters.
(h) 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.
(i) 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 width shall be thirty-six (36) inches.
(b) The maximum depth of the bottom of the wastewater infiltration trench shall be nine (9) 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.
(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).
(d) The depth of the fill cap shall provide a minimum of twelve (12) inches backfill above the top of the wastewater infiltration trench aggregate.
(e) The required fill cap must extend at least five (5) feet beyond the limits of the wastewater infiltration trenches and must taper to the original soil surface at a slope not to exceed 10 percent (see attached illustration). On sloping sites where serial distribution has been incorporated into the system design, on the lower side and ends of the wastewater infiltration trenches, the fill cap must extend to at least ten (10) feet beyond the limits of the wastewater infiltration trenches and must taper to the original soil surface at a slope not to exceed five (5) percent. The required property line setback shall be measured from the point at which the fill cap taper intersects with the naturally occurring soil surface. The fill cap must be installed prior to beginning trench installation when required on the construction permit.
(f) The required fill material must be soil texture Class I, Class II, or Class III, and be devoid of extraneous debris such as organic matter, building materials, etc.
(g) The wastewater infiltration trench aggregate shall be nine (9) inches in depth.
(h) All trees/brush removal shall be done in a manner that minimizes the disturbance or loss of naturally occurring soil.
(3) Final Landscaping and Drainage
(a) The septic tank and fill cap area shall be backfilled and shaped to promote the runoff of surface water.
(b) Where natural surface drainage does not exist, a swale shall be constructed adjacent to the fill cap area to divert surface water away from the onsite wastewater system to a positive outfall. The installation of ditches, curtain drains, and rain gutters may be required to intercept and divert water away from the onsite wastewater system location.
(c) A barrier to preclude parking and vehicular traffic over the system area may be required.
(d) Following final landscaping, seeding or sodding may be required to prevent erosion.
(e) 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.H