S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.N
(1) Site/Permitting Requirements
(a) The texture in the upper twelve (12) inches of naturally occurring soil must be Class I or Class II.
(b) The soil texture in the permeable substratum must be no more limiting than Class II.
(c) There must not be a zone of saturation (ZOS) within six (6) inches of the naturally occurring soil surface.
(d) The depth to any restrictive horizon must be greater than twelve (12) inches below the bottom of the proposed wastewater infiltration trenches.
(e) 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.
(f) No part of this system can be installed within one hundred twenty-five (125) feet of the critical area line or tidal waters as determined by the Department; or within one hundred twenty-five (125) feet of the ordinary high water elevation within the banks of non-tidal, environmentally sensitive waters.
(g) This system cannot be considered for facilities with peak flow rates in excess of four hundred eighty (480) gpd. In addition, this system shall not be considered for facilities requiring grease traps.
(h) This system must not be utilized on sites that require serial distribution. Level installations on sloping sites can be considered if it can be demonstrated that the entire installation (i.e., side wall to side wall and end to end) will meet the required textural limitations and the required offsets to the zone of saturation and restrictive horizons.
(i) The total linear footage of six (6) inch deep, thirty-six (36) inch wide wastewater infiltration trenches shall be increased by 100 percent over that which would be required for conventional trenches, as determined by the long-term acceptance rate of the permeable substratum.
(j) This system may be considered for installation on contiguous lots in new subdivisions approved after the effective date of this standard provided a setback of at least seventy-five (75) feet is maintained between the system and all adjacent property lines. The seventy-five (75) foot setback shall be measured from the point at which the fill cap taper intersects with the naturally occurring soil surface.
(2) Installation Requirements
(a) Site Preparation
(i) The naturally occurring soil surface underlying the area of the wastewater infiltration trenches shall be thoroughly tilled and mixed with the imported medium sand to a depth of six (6) inches.
(ii) All tree and brush removal shall be done in a manner that minimizes the disturbance or loss of naturally occurring soil.
(b) Fill and System
(i) The fill cap and buffer shall be Class I, Class II, or Class III.
(ii) The depth of the fill cap shall provide a minimum of twelve (12) inches backfill above the top of the wastewater infiltration trench aggregate.
(iii) 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).
(iv) The fill buffer shall be at least fifteen (15) feet in width.
(v) The fill taper shall be at least twenty (20) feet in width.
(vi) The required property line setback shall be measured from the point at which the fill cap taper intersects with the naturally occurring soil surface.
(vii) The total fill depth, excluding the taper zone, shall be at least eighteen (18) inches above the naturally occurring soil surface.
(viii) The wastewater infiltration trenches shall be installed in a Class I fill pad at least six (6) inches in depth, which extends five (5) feet beyond the trenches in all directions.
(ix) The wastewater infiltration trenches require a total aggregate depth of six (6) inches.
(x) The wastewater infiltration trench width shall be thirty-six (36) inches.
(xi) Infiltration trenches shall penetrate the permeable substratum and shall be at least two (2) feet in width containing USDA medium sand, washed concrete sand, or other material approved by the Department.
(xii) Effluent discharged to this system must receive a higher degree of treatment than that provided by a conventional septic tank (e.g., two (2) compartment septic tank or two (2) septic tanks in series).
(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 filled 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.N