S.C. Code Regs. § ch. 61, 61-56, 61-56.400, app 61-56.400.R
(1) Minimum Construction Requirements
(a) Only pipe having received written approval from the Department may be utilized in curtain drains. This approval shall be based upon the pipe meeting all applicable ASTM standards.
(b) The aggregate used in curtain drains shall be a material approved by the Department.
(c) The curtain drain trench utilizing tire chips or gravel or a similar type of Department approved product shall be at least six (6) inches wide.
(d) The curtain drain shall be placed ten (10) feet upslope and twenty-five (25) feet downslope of a subsurface wastewater infiltration area or repair area. Where the aggregate portion of the curtain is installed at the same or lower (downslope) elevation relative to an adjacent subsurface wastewater infiltration area or repair area, the aggregate portion of the curtain must be a minimum of twenty-five (25) feet from the adjacent subsurface wastewater infiltration area or repair area.
(e) The trench bottom shall have a uniform slope to the discharge point. Trench excavation with a ditch witch is permissible provided the trench bottom has a uniform downslope gradient.
(f) The solid discharge (non-aggregate) line shall be fifteen (15) feet from adjacent subsurface wastewater infiltration area or repair area.
(g) The downslope side of the trench toward the subsurface wastewater infiltration area shall have a minimum six (6) mil poly or an equivalent strength treated impervious material draped from the trench surface to the trench bottom to prevent groundwater from bridging the curtain drain.
(h) Agricultural drainpipe (slitted) with a minimum diameter of four (4) inches shall be placed along the trench bottom in the aggregate portion. Perforated pipe is acceptable, provided the perforations are installed facing either sideways or upward.
(i) There shall be at least two (2) inches of aggregate beneath the drainpipe.
(j) The aggregate shall be brought to at least six (6) inches from the ground surface.
(k) The aggregate shall be covered with a strong, untreated pervious material to prevent infiltration of back fill material.
(l) Solid drainpipe with a minimum diameter of four (4) inches shall be placed along the trench bottom from the aggregate to the discharge point.
(m) The curtain drain must discharge to the ground surface past the last wastewater infiltration trench line.
(n) Rodent barriers on discharge pipe outlet(s) are required.
(o) If the curtain drain's trench bottom depth exceeds thirty (30) inches, it shall be inspected prior to the aggregate being installed to ensure proper trench depth and grade. It is acceptable to place the pipe and aggregate in the trench prior to the final inspection when a probe rod inspection port can be used to accurately measure trench bottom depth.
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S.C. Code Regs. ch. 61, 61-56, 61-56.400, app 61-56.400.R