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.D - System Standard 220/221 - Shallow Placement with Six (6)-Inch Aggregate Depth

Current through Register Vol. 48, No. 6, June 28, 2024
(1) Site/Permitting Requirements
(a) There must not be a zone of saturation (ZOS) within
				  twenty-one (21) inches of the naturally occurring soil surface.
(b) The depth to any restrictive horizon must be greater than
				  twelve (12) inches below the bottom of the proposed wastewater infiltration
				  trenches.
(c) The texture in the upper eighteen (18) inches of
				  naturally occurring soil may either be Class I, Class II, Class III, or Class
				  IV.
(d) 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.
(e) Due to the decreased sidewall absorption area and the
				  increased potential for ground water mounding near the surface, the Equivalency
				  Factors for these systems shall be calculated by conventional wastewater
				  infiltration trenches and increased by an additional factor of 0.12
				  times.
(f) 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.
(g) 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.
(h) This system cannot be considered for facilities with peak
				  flow rates in excess of fifteen hundred (1500) gpd.
(2) Installation Requirements
(a) The wastewater infiltration trench aggregate shall be six
				  (6) inches in depth and shall be covered with at least nine (9) inches of
				  backfill.
(b) The wastewater infiltration trench width shall be
				  thirty-six (36) inches.
(c) The maximum depth of the bottom of the wastewater
				  infiltration trench shall be fifteen (15) inches below the naturally occurring
				  soil surface unless it can be demonstrated that deeper placement can meet the
				  required textural limitations and the offsets to the zone of saturation and
				  restrictive horizons.
(d) 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).
(e) All tree and brush removal shall be done in a manner that
				  minimizes the disturbance or loss of naturally occurring soil.
(3) Final Landscaping and Drainage
(a) Installation of drainage swales, ditches, curtain drains,
				  and rain gutters may be required to divert or intercept water away from the
				  onsite wastewater system location to a positive outfall. 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 system area 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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