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9. Distribution pipe used in trenches or beds for gravity <br />flow distribution shall be at least four (4) inches in diameter and <br />constructed of solid and durable material not subject to corrosion <br />or decay or to loss of strength under continuously wet conditions. <br /> <br />Agricultural drain tile shall be in twelve (12) inch <br />lengths and laid with one-fourth (1/4) inch open joints <br />on grade boards. All open joints shall be protected on <br />top by strips of asphalt treated building paper at least <br />ten (10) inches long and three (3) to six (6) inches wide <br />or by other acceptable means. <br /> <br />Other devices may be used to distribute sewage tank <br />effluent over the soil treatment area upon approval of <br />the administrator. <br /> <br /> 10. Distribution pipes used in trenches or beds for pressure <br />distribution shall be at least one inch in diameter and constructed <br />of sound and durable material not subject to corrosion or decay or <br />to loss of strength under continuously wet conditions. <br /> <br />Perforations shall be sized and spaced as shown in Table <br />I. <br /> <br /> 11. The distribution pipes shall be laid level or on a <br />uniform slope away from the distribution device of no more than <br />four (4) inches per one hundred (100) feet. <br /> <br /> 12. The distribution pipes in beds shall be uniformly spaced <br />no more than five (5) feet apart and not more than thirty (30) <br />inches from the side walls of the bed. <br /> <br /> 13. The drainfield rock shall completely encase the disposal <br />pipes to a depth of at least two (2) inches. The top of the <br />drainfield rock in trenches, beds, and mounds must be level in all <br />directions. <br /> <br /> 14. The filter material shall be covered with either a <br />permeable synthetic fabric or a four (4) inch layer of compacted <br />hay or straw covered with untreated building paper. Where a drop <br />box distribution system is used to fill a trench to within two <br />inches of the top of the drainfield rock, a permeable synthetic <br />fabric must be used to cover the drainfield rock. <br /> <br /> 15. The trenches or beds shall be backfilled with the <br />excavated material and slightly crowned above finished grade to <br />allow for settling. The backfill shall not be completed to a <br />density greater than that of the original soil. <br /> <br /> 16. The minimum depth of cover over the distribution pipes <br />shall be a least eight (8) inches. The maximum depth of cover over <br />the distribution pipes shall be no more than thirty-six (36) inches <br />and preferably no more than twenty-four (24) inches. <br /> <br /> <br />