South Carolina Code of Regulations › Chapter 61 - DEPARTMENT OF HEALTH AND ENVIRONMENTAL CONTROL › Subchapter 61-56 - ONSITE WASTEWATER SYSTEMS › Section 61-56.400 - Appendices of Standards for Permitted Systems › Appendix 61-56.400.I - System Standard 270/271 - Alternative Trench Width and Depth Systems

Current through Register Vol. 48, No. 6, June 28, 2024
(1) Site/Permitting Requirements
(a) 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 conventional or
				  alternative onsite wastewater systems.
(b) 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.
(c) This system cannot be considered for facilities with peak
				  flow rates in excess of fifteen hundred (1500) gpd unless the trench width is
				  three (3) feet and the aggregate depth is between fourteen (14) and
				  twenty-eight (28) inches.
(d) The linear footage requirement for an alternative width
				  and depth system shall be determined by first figuring the conventional
				  (thirty-six (36) inch wide with fourteen (14) inch aggregate depth) linear
				  footage requirements and then multiplying by the appropriate factor based on
				  desired trench width and aggregate depth. (See table below system illustration
				  for multiplication factors.)
(2) Installation Requirements
(a) Trench widths shall not exceed ten (10) feet.
(b) The aggregate depth shall be between six (6) inches and
				  twenty-eight (28) inches when considering trench widths ranging from one and
				  one-half (11/2) to ten (10) feet (see chart). The aggregate depth may be
				  increased to a maximum of forty-two (42) inches, provided the trench width does
				  not exceed thirty-six (36) inches (Note: In these cases, the equivalency
				  formula should be utilized to determine the appropriate factor (F) when
				  considering aggregate depths between twenty-eight (28) and forty-two (42)
				  inches). All trenches shall be covered with at least nine (9) inches of
				  backfill.
(c) Methods of construction which preclude vehicular
				  compaction of the trench bottom must always be utilized.
(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.
(d) Final approval shall be withheld until all landscaping
				  and drainage improvements have been satisfactorily completed.
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