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<br />I <br />I <br />I' <br />I' <br />I <br /> <br /> <br />- <br /> <br />11 <br /> <br /> <br />, <br /> <br />Ij <br />I: <br />I <br />I <br />I, <br />I <br /> <br /> <br />- <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />, <br /> <br />I <br /> <br />1 4. The filter material shall be covered with either a permeable synthetic fabric or a four <br />(4) inch layer of compacted hay or straw covered with untreated building paper. Where a drop <br />box distribution system is used to fill a trench to within two inches of the top of the drainfield <br />rock, a permeable synthetic fabric must be used to cover the drainfield rock. <br /> <br />1 5. The trenches or beds shall be backfilled with the excavated material and slightly <br />crowned above finished grade to allow for settling. The backfill shall not be completed toa <br />density greater than that of the original soil. <br /> <br />1 6. The minimum depth of cover over the distribution pipes shall be a least eight (8) <br />inches. The maximum depth of cover over the distribution pipes shall be no more than thirty- <br />six (36) inches and preferably no more than twenty-four (24) inches. <br /> <br />1 7. A grass cover shall be established by the owner or the owner's agent over the soil <br />treatmentarea. <br /> <br />Dual Field Systems <br /> <br />1. Dual field systems shall be used only where the percolation rate is slower than five <br />minutes per inch. <br /> <br />2. Dual field systems shall be sized, designed, and constructed as set forth above for <br />standard systems except as follows: <br /> <br />a The soil treatment area shall be divided into two or more parts. <br /> <br />b. Alternating soil treatment areas shall each be connected to a valve box outlet. <br /> <br />3. A part of the soil treatment area shall be used no more than one year unless inspection of <br />the effluent level indicates that a longer duration can be used. <br /> <br />Slowly Permeable Soils <br /> <br />1. Excavation for the purpose of constructing a soil treatment system must not be made in <br />any soil layer having a percolation rate slower than 120 minutes per inch. <br /> <br />2. Excavation for the purpose of constructing a soil treatment system must not be made in a <br />soil layer having a percolation rate slower than 60 minutes per inch unless the moisture <br />content is lower than the plastic limit of the soil. <br /> <br />3. Drainfield rock must not be placed in contact with original soil having a percolation rate <br />slower than 60 minutes per inch. <br /> <br />4. Where the percolation rate of the original soil is slower than 60 minutes per inch, at <br />least 12 inches of fill material having a texture defined as sand must be placed between the <br />drainfield rock and the original soil along the excavation bottom. <br /> <br />5. Construction equipment wheels or tracks must not be placed in contact with the bottom of <br />the excavation during the construction of a soil treatment system in soils having a percolation <br />rate slower than 15 minutes per inch. <br /> <br />6. The size of the soil treatment system must be based on an acceptance rate of 0.24 gallons <br />per square foot, which is equivalent to a sizing factor of 4.2 square feet per gallons per day. <br /> <br />49 <br />