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j~ ~ <br />1® <br />SECTION VI. t)EStGN CRITERIA (Atterna4eve UWas~water Systeraa~ <br />6.09 Evapotranspiration Disposal of Effluent <br />i <br />A, General: Evapotranspiration systems aze not permitted in Gilpin County due to <br />~ climatic conditions. <br />-~ 6.02 Sand Filter Systems <br />~ A. Sand filter systems shall be designed by an Registered Professional Engineer and may <br />. be designed to function with or without an tmderdrain system. If no underdrain <br />~ system is used, the design engineer shall verify that the surrounding soil is sufficiently <br />permeable to receive the effiuent from the sand filter. <br />'} E. The filtering material shall be clean, coazse sand, aU passing a screen having four (4) <br />~ meshes to the inch. The sand shall have an effective size between 025 and 0.6 mm. <br />~ The uniformity coefficient shall be 4.0 or less. <br />..p C. The sand shall be at feast two (2) feet deep below the distribution lines. The <br />~ distributors and underdrain, if required by the local board of health shall be <br />G surrounded by coarse screened gravel or crushed stone. <br />~ Underdrain effiuem must then be discharged via a soil absorption system or be further <br />1 D treated as necessary to meet receiving water standards or those of Section X as <br />~ applicable. <br />~ All of the gravel or stone shall pass a 2 '/z inch screen and shall be retained on a 3/4 <br />ad inch screen. Fine gravel 114 inch size or less may be used above and azound the <br />coazse material, both at the distributor and underdrains. The separating distance <br />~.~ between parallel distnbution lines shall not exceed six (6) feet, and a distnbution Line <br />. shall be. located within three {3) feet of each filter sidewall. Pipe for gravity <br />distribution shall be no less than four (4) inches in diameter. The slope of the <br />U distributors shall be 0.4 percent where dosing tanlrs aze not used, and the slope of the <br />underdrains 0.5 to 1.0 percent. The sand must be thoroughly settled by flooding or <br />d other means before distributors are placed at the final grade. The distributor and <br />underdrains shall be constructed of polyvinyl chloride or other material approved by <br />~ the local health department. <br />~ The top of the sand bed shall be no less than four (4) feet above the high ground <br />~ water table for installations in which effiuent percolates downward through soil. <br />~ 45 <br />D <br />