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§ 8.30 <br /> <br /> condition. Excavation shall be made onJy when the soil <br /> moisture content is at or less than the plastic <br /> <br /> 6. Vfhen the soft percolation rate at the bottom of the trench or <br /> bed is slower than 15 rn~nutes per inch, no vehicle or <br /> excavatfion equipment'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 remsdn on the <br /> surface soils. Excavation equipment or other vehicles shall <br /> not be driven on the soft treatment area. <br /> <br /> 7. There shall be a layer of at least 6 inches, but no more than <br /> 24 inches of drsdn~eld rock in the bottom of the trenches and <br /> beds. <br /> <br /> 8. V~here disposal trenches are constructed within 10 feet o£ <br /> trees 6 inches or larg~er in diameter, or dense shrubbery, or <br /> where it cmn reasonably be anti,pared that such'vegetation <br /> v~ll be present du~ln¢ the expected life of the system, at least <br /> 1£ inches of filter material shall be placed beneath the <br /> distribution p~pa. <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 a~d durable :uaterial not subject to <br /> corrosion or decay or to loss of streng~th under continuously <br /> wet conditions. <br /> a) Agricultural drain tile shall be in 12-inch lengths and <br /> 1Md with .£5-[uch open joints on grade boards. All open <br /> joints shall be protected on top by strips of asphalt <br /> treated b~]din¢ paper at least 10 inches lon~ and S to 6 <br /> inches wide or by other acceptable ~nea~s. <br /> b) Other devices may be used to distribute sewage tank <br /> effluent over the soil treatment area upon approval of <br /> the aSr~u~strator. . <br /> <br /> 10. Distribution pipes used in trenches or beds for pressure <br /> distribution shall be at least t ~nch in d~ameter and <br /> constructed of sound and durable material not subject to <br /> corrosion or decay or to loss of streng=th under continuously <br /> wet conditions. <br /> a) Perforations shall be sized and spaced as shown in <br /> Table I. <br /> <br />ll. The dist~bution pipes shall be laid level or on a uniform <br /> slope away from the distribution device of no more than 4 <br /> inches per 100 feet. <br /> <br />12. The distribution pipes ~_ beds shall be unifomn]y spaced no <br /> more than 5 feet apart and not more than S0 inches from the <br /> side walls of the bed. <br /> <br />Page 252 Printed 12/28,/90 <br /> <br /> <br />