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ft <br />C. Surface preparation or roughening may be performed with a <br />mold board plow, a disk plow, or a backhoe using only the <br />teeth. Mold board plow furrows shall be at least 8 inches <br />deep, shall be thrown upslope and shall run perpendicular to <br />the slope. There shall be no deadfurrow under the mound. <br />Disking may be used for surface preparation as a substitute <br />for mold board piowinq in soils having percolation rates <br />faster than 15 minutes per inch (sandy loam) in the top <br />8-inch depth. <br />backhoe teeth may be used to rougLen the soil surface and <br />break up the sod layer. Care must be taken so as not to <br />compact or puddle deeper soil layers. In no case shall any <br />surface soil be excavated and removed from the area. <br />D. Mound construction shall proceed immediately after surface <br />preparation is completed. Every effort should be taken to <br />prevent rain from falling on the prepared soil surface. <br />4. SIZE (See Figures 2 and 3 for layout and details) <br />A. The bottom area of the filter material (rock) was sized on <br />the basis of 0.83 square feet per gallon of waste per day, <br />yielding 500 square feet. <br />B. In no case shall the width of the filter mate ial (rock) in <br />a single bed exceed 10 feet. <br />5. CONSTRUCTION MATERIALS AND PROCEDURES <br />A. A minimum. of 12" of soil defined as sand she: be placed <br />where the filter i.iaterial is to be located. ti crawler <br />tractc�- with a blade or buck,,t shall be used to move the <br />sand into place. At least 6 inches of sand shall be kept <br />snder the tracks to minimize compaction of the plowed <br />layer. The sand layer upon which the filter material is <br />placed shall be level. <br />B. Sand is defined as a soil texture composed by weight of at <br />leact 25 percent of very coarse, coarse, and medium sand <br />varying in size from 2.0 to 0.25 mm, less than 50 percent <br />of fine or very fine sand ranging in size between 0.25 and <br />0.05 mm, and no more than 10 percent of particles smaller <br />than 0.05 run. <br />C. A depth of at least 9 inches of filer material (rock) shall <br />be placed on the sand layer prior to installing the distri- <br />bution pipe. <br />- 9 -- <br />