S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.O
(1) Site/Permitting Requirements
(a) The texture in the upper eighteen (18) inches of naturally occurring soil must be Class I or Class II.
(b) The absorption bed within the mound shall be sized on the long-term acceptance rate of the most limiting texture in the upper eighteen (18) inches of naturally occurring soil.
(c) The linear footage of the absorption bed shall be determined in accordance with Standard 270.
(d) The absorption bed width shall be a minimum of five (5) feet and a maximum of 10 feet.
(e) Mounded fill systems must not be placed on sites with a slope in excess of three (3) percent.
(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. Because of the long buffer, side slope, fill pad, and taper associated with this system, the one hundred twenty-five (125) foot setback shall be measured from the outer edge of the aggregate bed within the mound.
(g) 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.
(h) 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.
(i) 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).
(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. Because of the long buffer, side slope, fill pad, and taper associated with this system, the seventy-five (75) foot setback shall be measured from the outer edge of the aggregate bed within the mound.
(2) Installation Requirements
(a) Site Preparation
(i) If present within eighteen (18) inches of the naturally occurring soil surface, organic material and restrictive horizons must be removed from beneath the mound and replaced with USDA medium sand, washed concrete sand, or an equivalent material approved by the Department. The replacement area must extend five (5) feet in all directions beyond the edges of the aggregate filled absorption bed.
(ii) The naturally occurring soil surface underlying the mound shall be thoroughly tilled and mixed with the imported mound fill material to a depth of six (6) inches.
(b) Mound/Absorption Bed Requirements
(i) Low Pressure Pipe Distribution (LPP) must be utilized to preclude localized hydraulic overloading of the imported fill material and to minimize the impact on the shallow zone of saturation.
(ii) Low Pressure Pipe Distribution (LPP) must be designed and installed in accordance with Department standards or equivalent designs. The size and layout of each distribution system will vary based on the size of the filter and the needed dosing.
(iii) Pump design shall be in accordance with Department standards.
(iv) There must be at least twenty-four (24) inches of medium sand placed between the naturally occurring soil surface and the bottom of the absorption bed. The bottom surface of the absorption bed must be placed at least twenty-four (24) inches above the zone of saturation.
(v) If the slope of the site in the proposed mound area is one (1) percent or less, then the mound shall be placed on a twelve (12) inch fill pad which must extend twenty (20) feet beyond the mound in all directions. If the slope of the site in the proposed mound area is greater than one (1) percent but less than or equal to three (3) percent, then the mound shall be placed on a twelve (12) inch deep fill pad which must extend twenty (20) feet beyond the mound area on the sides of the mound; forty (40) feet beyond the mound area on the downslope side of the mound; with no fill pad required on the upslope side of the mound.
(vi) The mound and fill pad material shall be USDA medium sand, washed concrete sand, or other equivalent material approved by the Department.
(vii) The depth of the fill cap material above the absorption bed shall be nine (9) to fifteen (15) inches of soil texture Class II or Class III. Sod may be substituted for four (4) inches of this portion of the fill cap material.
(viii) The depth of the fill cap material above the mound side-slope, the twelve (12) inch deep fill pad, and the taper shall be at least four (4) inches of soil texture Class II or Class III. Sod may be substituted for this portion of the fill cap material.
(ix) A 1:2 maximum slope is required if the mound side-slope and taper are sodded.
(x) A 1:4 maximum slope is required if the mound side-slope and taper are mulched and seeded.
(3) Final Landscaping and Drainage
(a) The septic tank and mound 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.
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S.C. Code Regs. ch. 61, 61-56, 61-56.400, app 61-56.400.O