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r t SECTION 6: DRAINFIELDS OR SOIL TREATMENT AREA I A. Location ' 1. On slopes in excess of 12 percent the soil profile shall be carefully evaluated in the location of the ` proposed soil treatment area and downslope to identify _ the presence of layers that may cause sidehill seepage. In no case shall. a trench be located within 15 feet of such a layer surfacing on the downslope. 2. Bed construction shall be limited to areas having I natural slopes of less than six percent. (� B. Design and Construction - 1. The bottom of trenches and beds shall be at least four ' feet above the watertable or bedrock. 2. The trenches shall be not less than 18 inches nor more fthan 36 inches wide. Any trench wider than 36 inches shall.be considered a bed. [; 3. Trenches and beds shall be. not more than 100 feet in length. 4. The bottom of the trench or bed excavation shall be level. [, 5. The bottom and sides of the trench or bed excavation to the level of the filter material shall be scarified _ to remove smears left by the construction equipment and _ footprints. All loose material shall be removed from .the excavation. The bottom of the excavation shall not - be driven on after scarification. 6. When the soil percolation rate at the bottom of the trench or bed is slower than 15 minutes per inch, no vehicle or .excavator shall be allowed to drive on after scarification. 7. There shall'be a layer of at least six but no more than .24 inches of filter material in the bottom.of the trenches and beds. '. 8. Where disposal trenches are constructed*within ten feet of trees six inches or larger in diameter, or dense shrubbery, or where it -can reasonably be anticipated that such vegetation will be present 'during the expected life of the system, at least 12 inches of filter material shall be placed beneath the distribution pipe. =37