S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.K
(1) Site/Permitting Requirements
(a) The depth to any restrictive horizon must be greater than twelve (12) inches below the bottom of the proposed wastewater infiltration trenches.
(b) The texture in the upper eighteen (18) inches of naturally occurring soil must be no more limiting than Class III.
(c) Soil conditions, the depth to rock and other restrictive horizons, the depth to the zone of saturation (ZOS), and the elevation differential between the septic tank outlet and the highest wastewater infiltration trench(es) must meet applicable standards for alternative onsite wastewater systems.
(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.
(e) This system cannot be considered for facilities with peak flow rates in excess of six hundred (600) gpd.
(f) The linear footage requirement for an alternative width and depth system shall be determined by first figuring the conventional (36-inch-wide with 14-inch aggregate depth) linear footage requirements and then multiplying by the appropriate factor based on desired trench width and aggregate depth as computed in the following table:
FACTOR (F) FOR MAINTAINING EQUIVALENT INFILTRATIVE SURFACE AREA | |||
TRENCH WIDTH (ft.) | AGGREGATE DEPTH (in.) | ||
6" * | 9" ** | # OF DISTRIBUTION PIPES | |
MULTIPLICATION FACTOR | |||
4' | 1.20 | 1.06 | 1 |
5' | 1.00 | 0.89 | 1 |
6' | 0.85 | 0.78 | 2 |
7' | 0.74 | 0.68 | 2 |
8' | 0.66 | 0.61 | 2 |
9' | 0.59 | 0.55 | 3 |
10' | 0.54 | 0.51 | 3 |
* Factors reflect a twelve (12) percent increase ** Factors reflect a nine (9) percent increase | |||
(g) This system may only be installed on sites where the long-term acceptance rate (LTAR) for the system will be between 1.0 and 0.5 gpd per foot squared (gpd/ft2). The bottom of the absorption field cannot be installed in Class IV soils (0.4 to 0.1 LTAR).
(h) The distribution pipes in the bed shall be at least eighteen (18) inches from the edge of the trench and located on three (3) foot centers.
(i) 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.
(j) 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.
(2) Installation Requirements
(a) Trench widths shall not exceed ten (10) feet.
(b) Wide trenches should be installed by excavating from the sides. Heavy equipment, such as backhoes, may not be placed in the trenches in order to avoid soil compaction.
(c) 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 ten (10) percent. 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.
(3) Final Landscaping and Drainage
(a) Installation of drainage swales, ditches, diversion drains, or 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) A barrier to preclude parking and vehicular traffic over the area of the system may be required.
(c) Following final landscaping, seeding, or sodding may be required to prevent erosion.
S.C. Code Regs. ch. 61, 61-56, 61-56.400, app 61-56.400.K