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Effective April 28, 2015 Chapter Four Subsurface Sewage Treatment System Regulations <br />must be used. At least six inches of sand must be kept beneath equipment to minimize <br />compaction of the prepared surface. <br />(0) A minimum of 12 inches of clean sand must be placed in contact with the bottom area of the <br />mound distribution media bed and must be uniformly tapered to cover the entire original soil <br />absorption area. Other sandy materials are allowed to be used outside of this area to <br />complete construction of the mound. <br />(P) The top of the clean sand layer upon which the mound distribution media bed is placed must <br />be level in all directions. <br />(Q) A vertical inspection pipe at least four inches in diameter must be installed and secured at <br />the distribution medium and sand interface. The inspection pipe must have three -eighths <br />inch or larger perforations spaced vertically no more than six inches apart. At least two <br />perforations must be located in the distribution medium. Perforations must not be located <br />above the permeable synthetic fabric, if used. The inspection pipe must extend to the <br />bottom of the distribution medium, be secured, and be capped, flush with or above finished <br />grade. <br />(R) On slopes of one percent or greater, the upslope edge of the mound absorption bed must be <br />placed on the contour. <br />(S) The sidewalls of the mound absorption bed must be as vertical as practical and not <br />intentionally sloped. <br />(T) A minimum of six inches of sand, sandy loam or loam material must be placed on the top of <br />the mound absorption bed and sloped upwards towards the center of the mound a minimum <br />of ten horizontal units to one vertical unit. <br />(U) Construction vehicles must not be allowed on the distribution media until backfill is placed. <br />(V) A minimum of six inches of topsoil borrow must be placed over the entire mound. <br />(W) A vegetative cover must be established over the entire area of the mound. The mound shall <br />be protected until a vegetative cover is established by use of erosion control. The <br />established vegetative cover shall not interfere with the hydraulic performance of the system <br />and shall provide adequate frost and erosion protection. <br />17.4 At -Grade Systems <br />(1) At -Grade Systems. To qualify as an at -grade system, the system must meet or exceed the <br />following requirements: <br />(A) Employ flow values in Section 12. <br />(B) Meet or exceed the applicable technical requirements of Section 13, Section 14, and Section <br />15. <br />(C) Meet or exceed the requirements of Sections 16.2 and 16.3. <br />(2) Location of At -Grade Systems <br />(A) The upper 12 inches of the absorption area must have a loading rate of 0.45 gallons per day <br />per square foot or greater as shown in Table VI or Table VIa. <br />(B) At -grade systems must not be installed in areas with slopes greater than 12 percent. <br />(C) Setbacks must be according to Table V. Setbacks must be measured from the original soil <br />absorption area. <br />(3) Design and Construction of At -Grade Systems <br />(A) The at -grade absorption width must be determined by dividing the contour loading rate, <br />according to Section 16.3 (13), by the soil loading rate, and must not exceed a width of 15 <br />feet. The at -grade absorption width for slopes of one percent or greater does not include any <br />width of the media necessary to support the upslope side of the pipe. <br />(B) The at -grade absorption length must be calculated by dividing the design flow by the soil <br />loading rate found in Table VI or VIa, for the upper 12 inches of soil and dividing by the <br />absorption bed width. <br />70 Washington County Development Code <br />