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.H - System Standard 260/261 - 9-Inch Shallow Placement System with Fill Cap

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
				  fifteen (15) 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 must be no more limiting than Class III.
(d) 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.
(e) 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.
(f) 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 0.09
				  times.
(g) No part of this system can be installed within 125 feet
				  of the critical area line or tidal waters as determined by the Department; or
				  within 125 feet of the ordinary high water elevation within the banks of
				  non-tidal, environmentally sensitive waters.
(h) 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.
(i) 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 width shall be
				  thirty-six (36) inches.
(b) The maximum depth of the bottom of the wastewater
				  infiltration trench shall be nine (9) 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.
(c) 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).
(d) The depth of the fill cap shall provide a minimum of
				  twelve (12) inches backfill above the top of the wastewater infiltration trench
				  aggregate.
(e) 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 10 percent (see attached
				  illustration). 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.
(f) The required fill material must be soil texture Class I,
				  Class II, or Class III, and be devoid of extraneous debris such as organic
				  matter, building materials, etc.
(g) The wastewater infiltration trench aggregate shall be
				  nine (9) inches in depth.
(h) All trees/brush removal shall be done in a manner that
				  minimizes the disturbance or loss of naturally occurring soil.
(3) Final Landscaping and Drainage
(a) The septic tank and fill cap 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 fill cap 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.
Click to
				  view image