ll be: 2 ft of fill below the trench bottom, plus 9 in. of trench depth, plus 1 ft of fill, or a total of 3 ft 9 in. (3.75 ft). The edge of the mound uphill from the trench will stick out 3.75 ft X 3/1 = 11.25 ft = 11 ft 3 in. if we choose a three to one slope. Actually, the distance would be a little less because the ground is rising to meet the mound side. As long as the uphill side is at least 10 ft wide and has a slope no steeper than three to one, don't worry about the difference due to ground slope. The sides of the mound also must have a maximum slope of three to one, and must extend at least 10 ft from the ends of the excava- tion. For our example mound, we will extend the sides 11 ft 3 in. beyond each end of the trench. The height of the mound at the downhill edge of the trench will be 4 in. greater than at the uphill edge. The total height will be 3.75 ft plus 0.3 ft or 4.05 ft. Call it 4 ft. On the downhill side of the mound, the natural ground slope must be considered, since in order to maintain a proper slope, this side must be considerably longer than would be the case on flat ground. Since only the area under and downhill from the mound's absorption trench can be counted as basal absorption area, it is with this downhill extension that we pick up the extra absorption area we need. The formula for calculating the distance that the mound side ONSITE WASTEWATER DISPOSAL Table 6.4 Correction Factors for Natural Ground Slope 3:1 Mound Slope 4:1 Mound Slope Slope (%) Correction Factor Correction Factor 10.11 should extend downhill from the downhill edge of the trench or bed downhill side = mound height at downhill edge of trench or bed X correction factor. The correction factors are given in Table 6.4. Note: Percent slope is the vertical drop divided by the horizontal distance. That ratio is the arc tangent of the degrees of slope. For our example mound, the height of the mound at the downhill edge of the trench is 4 ft, the mound slope is three to one, and the ground slope is 6%. So downhill side = 4 ft