(a)   Design.
      (1)   Distance to rock.  The minimum acceptable separation distance, both vertical and horizontal, from the absorption trench bottom and sidewalls to lithic rock, rock outcroppings, Cr horizons and pans, is 12 inches.  However, in the limestone overlay district, horizontal and vertical separation between limestone lithic rock and trench bottoms and sidewalls is 48 inches for septic tank effluent, 36 inches for TL-2 effluent and 24 inches for TL-3 effluent with ultraviolet or other approved standard disinfection.
      (2)   Depth to seasonal water table.  The minimum separation distance from the absorption trench bottom or point of effluent release to the seasonal water table is 24 inches for septic tank effluent, 18 inches for TL-2 effluent, and 12 inches for TL-3 effluent with ultraviolet or other approved standard disinfection.
      (3)   Blasting of lithic rock prohibited.  The use of explosive materials for the purpose of removing lithic rock within 100 feet of the soil absorption area or within fifty feet of any remaining portion of the sewage conveyance, treatment or dosing system in the limestone overlay district is specifically prohibited.  Lithic rock encountered in the soil absorption area during installation at any location will necessitate a redesign of the system permitted and will be handled on a case-by-case basis.
      (4)   Size.  The size of the soil absorption area based on the square footage of the trench bottoms shall consist of a minimum of 600 square feet. Drip and spray or other surface square footage designed systems shall have a minimum square footage of 1800 sq. ft.
      (5)   Driveways and parking areas. Driveways and parking areas shall be a minimum of 5 feet from onsite sewage treatment systems except for sewer and conveyance lines crossing the area and soil absorption areas designed to be placed under paved surfaces.
      (6)   Minimum location requirements. Minimum location requirements as set forth in Appendix I, following this chapter shall be met.
   (b)   Off Site Easements. Where an onsite sewage treatment system is located by easement off the lot of the structure it serves, the Health Director shall establish special design and performance standards, procedures and forms necessary to ensure identification, protection and maintenance of the onsite sewage treatment system to be located on that easement.
   The onsite sewage treatment system shall be located on the lot, tract or parcel of land which it serves. However, onsite sewage treatment systems on off-site easements may be permitted in the following situations:
         (1)   A permit was issued for the onsite sewage treatment system prior to January 17, 1989.
         (2)   The onsite sewage treatment system is proposed to replace a failing onsite sewage treatment system.
         (3)   The lot was shown to be served by the off-site easement on a preliminary plan of subdivision approved prior to January 17, 1989.
         (4)   The lot was shown on a preliminary plan of subdivision or plan of family subdivision accepted for review by the Department of Planning, Zoning and Community Development prior to January 17, 1989.
         (5)   The onsite sewage treatment system is proposed to serve an existing lot of record as of January 17, 1989, for which no approved on-site sewage treatment system approvable for a minimum design of 450 gallons per day can be found.
         (6)   Onsite sewage treatment systems may be situated on permanent, dedicated open space, but only where specifically permitted by the Subdivision Regulations and the Zoning Ordinance of the County.
         (7)   Multiple existing structures on any parcel currently served by on- site sewage treatment systems may use easements for onsite sewage treatment systems if a division of that parcel cannot be reasonably accomplished without the use of easements.
   (c)   Reserve Absorption Area Sites.  Sufficient suitable soils shall be available on each lot, or available to each lot by easement or other device approved by the Health Department, to allow repair and/or extension of the on-site sewage treatment system for a period of time equal to:
         (1)   The reasonably anticipated life expectancy of the structure (interpreted as 100 percent repair area); or
         (2)   In an area designated by an adopted area plan for future central sewer service by Loudoun Water or an incorporated town, the planned availability date of that sewer service or fifty percent of the originally required soil area, whichever is greater. 
   Soil absorption areas are considered, for purposes of this section, to have a life expectancy of thirty years.  Lots proposed for approval in these areas shall contain sewer utility easements designed to facilitate future sewer line construction and installation.  Design consultation with Loudoun Water or other local sewage authorities is required prior to Health Department approval.
   (d)   Site Preparation and Alteration.
         (1)   Removal of vegetation.  Vegetation, such as maples, willows and other plant species with extremely hydrophilic (water loving) root systems, shall be removed at least ten feet from the actual absorption areas.  All trees should be removed from the absorption area.  The local agent of the Virginia Department of Forestry will arbitrate any dispute as to the hydrophilic nature of any tree or shrub.
         (2)   Placement of utilities. Subsurface soil absorption systems shall not be placed in an underground utility easement.  No buried utility services, water lines, electrical lines, gas lines, etc., shall traverse the subsurface soil absorption system area, nor shall the buried service be closer than ten feet to the system.
(Ord. 94-05.  Passed 2-16-94; Ord. 17-03.  Passed 1-19-17.)