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§/;.30 <br /> <br />Page 252 <br /> <br /> condition. Excavation shall be made only when the soil <br /> moisture content is at or less than the plastic <br /> <br /> 6. When the soil percolation rate at the bottom of the trench or <br /> bed is slower than 15 rn~nutes per inch, no vehicle or <br /> excavation equ~pment'shall be allowed on the trench or bed <br /> area. Excavation shall be by back hoe or other means that <br /> allow the equipment wheels or tracks to remain on the <br /> suzface soils. Excavation equipment or other vetfictes shall <br /> not be driven on the soil treatment area. <br /> <br /> 7. There shall be a layer of at least 6 inches, but no more than <br /> 24 inches of ch-ainfield rock in the bottom of the trenches and <br /> beds. <br /> <br /> 8. Where disposal trenches are constructed wdthin 10 feet of <br /> trees 6 inches or larger in diameter, or dense shrubbery, or <br /> where it can reasonably be antidpated that such:vegetation <br /> will be present during the expected life of the system, at least <br /> 12 inches of filter material shall be placed beneath the <br /> clistribution pipe. <br /> <br />9. Distribution pipe used in trenches or beds for gravity flow <br /> distribution shall be at least 4 inches in diameter and <br /> constructed of solid and durable :uaterial not subject to <br /> corrosion or decay or to loss of strength under continuously <br /> wet conditions. <br /> a) Agricultural drain tile shall be in 12-inch lengths and <br /> la~d with .2S-inch open joints on grade boards. Ail open <br /> joints shall be protected on top by strips of asphalt <br /> treated b~lH~ng paper at least 10 inches long amd 3 to 6 <br /> inches wdde or by other acceptable meeos. <br /> b) Other devices may be used to distribute sewage tank <br /> effluent over the soil treatment area upon approval of <br /> the administrator. <br /> <br />I0. Distribution pipes used in trenches or beds for pressure <br /> distribution shall be at least 1 inch in diameter and <br /> constructed of sound and durable material not subject to <br /> corrosion or decay or to loss of strength under continuously <br /> wet conditions. <br /> a) Perforations shaI1 be sized and spaced as shown in <br /> Table I. <br /> <br />11. The ~st~bution pipes shall be laid level or on a uniform <br /> slope away from the distribution devSce of no more than 4 <br /> inches per 100 feet. <br /> <br />12. The d~stribut~on pipes in beds shall be uniform]>, spaced no <br /> more than $ feet apart a_nd not more than S0 inches from the <br /> side walls of the bed. <br /> <br />Printed 12/28,/90 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I. <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />I <br />I <br />I <br />I <br /> <br /> <br />