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Effective April 28, 2015 Chapter Four Subsurface Sewage Treatment System Regulations <br />Clay, sandy clay, silty <br />clay <br />*Only includes soil horizons with <50% rock fragments, with very friable and friable consistence, and loose non - <br />cemented sands. Soil horizons with >50% rock fragments must not come in contact with soil dispersal system <br />media. <br />** Conduct percolation test and size under Table VIa. May need to be designed as a Type III System under Section <br />19 of this Chapter. <br />*** Assume a hydraulic loading rate to the sand at 1.6 gpd/ft2. <br />Table VIa <br />Loading Rates for Determining Bottom Absorption Area and Absorption Ratios using Percolation Tests <br />Treatment Level C <br />Treatment Level C <br />Treatment Levels A, <br />Treatment Levels A, <br />Percolation Rate <br />Absorption Area <br />Mound Absorption <br />A-2, B, and B-2 <br />A-2, B, and B-2 <br />(Minutes Per Inch) <br />Loading Rate <br />Ratio <br />Absorption Area <br />Mound Absorption <br />(gpd/ <br />Loading Rate d/ft2) <br />Ratio <br /><0.1 <br />- <br />1.0 <br />- <br />1.0 <br />0.1 to 5 <br />1.2 <br />1.0 <br />1.6 <br />1.0 <br />0.1 to 5 (fine sand <br />0.6 <br />2.0 <br />1.0 <br />1.6 <br />and loamy fine sand <br />6 to 15 <br />0.78 <br />1.5 <br />1.0 <br />1.6 <br />16 to 30 <br />0.6 <br />2.0 <br />0.78 <br />2.0 <br />31 to 45 <br />0.5 <br />2.4 <br />0.78 <br />2.0 <br />46 to 60 <br />0.45 <br />2.6 <br />0.6 <br />2.6 <br />>60* <br />- <br />- <br />- <br />- <br />** Soil with too high a percentage of clay for installation of a Type I, or Type II system. <br />Systems in soils with this Percolation Rate must be a Type 111, Type IV or Type V system. <br />(6) If drainfield rock medium is employed, a durable, nonwoven geotextile fabric must be used to <br />cover the distribution rock medium. The fabric must be of sufficient strength to undergo <br />installation without rupture. The fabric must permit passage of water without passage of overlying <br />soil material into the rock medium. <br />(7) All excavation into the absorption area, or surface preparation of the upper 12 inches of the <br />absorption area, must be in a manner to expose the original soil structure in an unsmeared and <br />uncompacted condition. Excavation is only allowed when the soil moisture content is at or less <br />than the plastic limit and is not frozen or freezing. <br />(8) Excavation equipment or other vehicles must not be driven on the excavated or prepared absorption <br />area. Foot traffic on these areas must be minimized and not cause compaction. The exposed areas <br />must be immediately covered with the media or designed coverage materials. If the areas are <br />exposed to direct rainfall, they must be allowed to dry and must be re -prepared according to Section <br />17.3(3)(J ). <br />(9) A minimum of six inches of topsoil borrow shall be placed over the system. <br />(10) A close -growing, vigorous vegetative cover must be established over the soil treatment and <br />dispersal system and other vegetatively disturbed areas. The sodding, seeding, or vegetation <br />establishment shall begin immediately after the placement of the topsoil borrow. If the climatic <br />season does not allow immediate establishment of vegetation, the soil treatment and dispersal <br />system must be protected from erosion and excessive frost and a vegetative cover must be <br />established as soon as favorable climatic conditions exist. The vegetative cover established must <br />not interfere with the hydraulic performance of the system and shall provide adequate frost and <br />erosion protection. Trees, shrubs, deep-rooted plants, or hydrophytic plants must not be planted on <br />the system. <br />63 Washington County Development Code <br />