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• <br />(2) The invert of the inlet pipe shall be at least one inch <br />higher than the invert of the outlet pipe to the next trench. <br />(3) The invert of the outlet pipe to the next trench shall be at <br />least two inches higher than the invert of the outlet pipe <br />of the trench in which the box is located. <br />(4) When sewage tank effluent is delivered to the drop box by a <br />pump, the pump discharge shall be directed against a wall or <br />side of the box on which there is no outlet. <br />(5) The drop box shall have a removable cover either flush or <br />above finished grade or covered by no more than six inches <br />of soil. <br />IV. DRAINFIELD - Final treatment and disposal of all sewage tank <br />effluent shall be by means of soil treatment. <br />1. SIZING <br />Indicated average percolation rat is 27.5 minutes per inch for <br />the primary site and 23.3 minutes per inch for the alternate site. <br />A. Total a ainfield area is 1002 ft2 <br />• B. Drainfield trench bottom width is 31. <br />C. TOTAL lineal feet of drain tile is 3349. <br />D. This requires 5 laterals of 66' in length. <br />See Figure 1 for typical plac3ment. <br />E. Minimum spacing of laterals is 7.5 feet from center to center. <br />2. LOCATION <br />A. On slopes in excess of 12 percent the soil profile FiAall be <br />carefully evaluated in the location of the propoe-4d soil treat- <br />ment area and downslope to identify the presence of layers <br />that may cause sidehill seepage. In no case shall. a trench be <br />located within 15 feet of such a layer surfacing on the downslope. <br />B. Bt ;onstruction shall be .limited to areas having natural slopes <br />of less than six percent. <br />C. Any soil treatment area other than seepage pits shall be set <br />back the following distances from the features gl.ven below: <br />• <br />