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6. 7. 8. 9. 10. 11. 12. 13. 14. Mounds shall not be located on slopes exceeding six per cent (6%) if the soil percolation rate is slower than thirty (30) minutes per inch to a depth of at least twenty-four (24) inches below the sand layer. I I I I I I I I I I I I I I I I I I I Mounds shall not be located on natural slopes exceeding twelve per cent (12%) under any soil percolation rate conditions. The bottom area of the filter material shall be sized on the basis of two hundred (200) square feet per bedroom or eighty-three hundredths (0.83) square feet per gallon of waste per day. In no case shall the width of the filter material in a single bed exceed ten (10) feet. A rubber tired tractor may be used for plowing or disking, but in no case shall a rubber tired tractor be used after the surface preparation is completed. A crawler or track-type tractor shall be used for mound construction where the soil percolation rate is slower than 15 minutes per inch. The discharge pipe from the pump to the mound area shall be installed prior to soil surface preparation. The trench shall be carefully backfilled and compacted to prevent seepage of effluent. Soil Surface Preparation. a. All vegetation in excess of four inches in length and dead organic debris must be removed from the surface of the total area selected for the mound, including the area under the banks. b. The total area selected for the mound, including the dikes, shall be plowed to a depth of at least eight (8) inches. Furrows shall run perpendicular to the direction of slopes. All furrows shall be thrown uphill and there shall be no deadfurrow under the mound. The soil shall be plowed only when the moisture content of a fragment eight (8) inches below the surface is below the plastic limit. c. In soils having percolation rates faster than fifteen (15) minutes per inch (sandy loams) in the top eight (8) inch depth, disking may be used for surface preparation as a substitute for plowing. d. Mound construction shall proceed immediately after surface preparation is completed. e. The original soil must not be excavated or moved more than one foot from its original location during soil surface preparation. A minimum of twelve (12) inches of soil defmed as sand shall be placed where the filter material is to be located. A crawler tractor with a blade shall be used to move the sand into place. At least six (6) inches of sand shall be kept under the tracks to minimize compaction of the plowed layer. The sand layer upon which the filter material is placed shall be level. A depth of at least nine (9) inches of filter material shall be placed over the bed area below the distribution pipe. 56