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.N - System Standard 420/421 - Mounded Infiltration System

Current through Register Vol. 48, No. 6, June 28, 2024
(1) Site/Permitting Requirements
(a) The texture in the upper twelve (12) inches of naturally
				  occurring soil must be Class I or Class II.
(b) The soil texture in the permeable substratum must be no
				  more limiting than Class II.
(c) There must not be a zone of saturation (ZOS) within six
				  (6) inches of the naturally occurring soil surface.
(d) The depth to any restrictive horizon must be greater than
				  twelve (12) inches below the bottom of the proposed wastewater infiltration
				  trenches.
(e) 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.
(f) No part of this system can be installed within one
				  hundred twenty-five (125) feet of the critical area line or tidal waters as
				  determined by the Department; or within one hundred twenty-five (125) feet of
				  the ordinary high water elevation within the banks of non-tidal,
				  environmentally sensitive waters.
(g) This system cannot be considered for facilities with peak
				  flow rates in excess of four hundred eighty (480) gpd. In addition, this system
				  shall not be considered for facilities requiring grease traps.
(h) This system must not be utilized on sites that require
				  serial distribution. Level installations on sloping sites can be considered if
				  it can be demonstrated that the entire installation (i.e., side wall to side
				  wall and end to end) will meet the required textural limitations and the
				  required offsets to the zone of saturation and restrictive horizons.
(i) The total linear footage of six (6) inch deep, thirty-six
				  (36) inch wide wastewater infiltration trenches shall be increased by 100
				  percent over that which would be required for conventional trenches, as
				  determined by the long-term acceptance rate of the permeable substratum.
(j) This system may be considered for installation on
				  contiguous lots in new subdivisions approved after the effective date of this
				  standard provided a setback of at least seventy-five (75) feet is maintained
				  between the system and all adjacent property lines. The seventy-five (75) foot
				  setback shall be measured from the point at which the fill cap taper intersects
				  with the naturally occurring soil surface.
(2) Installation Requirements
(a) Site Preparation
(i) The naturally occurring soil surface underlying the area
				  of the wastewater infiltration trenches shall be thoroughly tilled and mixed
				  with the imported medium sand to a depth of six (6) inches.
(ii) All tree and brush removal shall be done in a manner
				  that minimizes the disturbance or loss of naturally occurring soil.
(b) Fill and System
(i) The fill cap and buffer shall be Class I, Class II, or
				  Class III.
(ii) The depth of the fill cap shall provide a minimum of
				  twelve (12) inches backfill above the top of the wastewater infiltration trench
				  aggregate.
(iii) 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).
(iv) The fill buffer shall be at least fifteen (15) feet in
				  width.
(v) The fill taper shall be at least twenty (20) feet in
				  width.
(vi) The required property line setback shall be measured
				  from the point at which the fill cap taper intersects with the naturally
				  occurring soil surface.
(vii) The total fill depth, excluding the taper zone, shall
				  be at least eighteen (18) inches above the naturally occurring soil
				  surface.
(viii) The wastewater infiltration trenches shall be
				  installed in a Class I fill pad at least six (6) inches in depth, which extends
				  five (5) feet beyond the trenches in all directions.
(ix) The wastewater infiltration trenches require a total
				  aggregate depth of six (6) inches.
(x) The wastewater infiltration trench width shall be
				  thirty-six (36) inches.
(xi) Infiltration trenches shall penetrate the permeable
				  substratum and shall be at least two (2) feet in width containing USDA medium
				  sand, washed concrete sand, or other material approved by the
				  Department.
(xii) Effluent discharged to this system must receive a
				  higher degree of treatment than that provided by a conventional septic tank
				  (e.g., two (2) compartment septic tank or two (2) septic tanks in
				  series).
(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 filled 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.
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