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Table 3-23 Roaf Runoff Dispersion System Sizing <br />Trench Dimensions Required Length af Trench per 100 square feet of Roof Surface** <br />viidth depth* coarse sand sand loamy sand sandy loam loam <br />1.5 fi. 1.0 ft. 0.48 0.95 2.24 3.60 5.16 <br />1.5 ft. 037 0.72 1.G7 2.68 3.78 <br />2.0 fr. 0.29 0.59 135 2.16 3.00 <br />2S fl. 0.25 0.49 L13 1.80 2.50 <br />3.0 R. 0.21 0.43 0.98 1.55 2.14 <br />2.0 ft. I.0 ft. 0.40 0.78 1.77 2.86 4.08 <br />1.5 R. 0.31 0.61 134 2.16 3.00 <br />2.0 ft. 0.25 Q50 1.09 1.74 2.42 <br />2.5 ft. 0.21 0.42 0.93 1.47 2.04 <br />3.0 (t. 0.13 037 0.81 1.27 1.74 <br />2.5 R. 1.0 ft. 034 0.67 1.48 2.38 336 <br />I.5 ft. 0.26 0.52 1.13 1.80 2.54 <br />2.0 ft. 0.22 0.43 0.92 1.46 2.06 <br />2.5 ft. 0.18 037 0.79 I?4 1.73 <br />3.0 R. 0.16 Q.32 0.69 1.07 1.49 <br />3.0 ft. IA ft. 0.29 0.58 1.27 2.oa 2.90 <br />I.5 R. 0.23 0.4G 0.97 1.55 2.20 <br />2.0 R. O.I9 033 0.80 I:1G 1.79 <br />?.5 ft. 0.1G 032 0.68 1.07 I51 <br />3.0 ft. 0.14 0.28 0.G0 0.93 131 <br />3.5 ft. I.0 ft. 0?G 0.51 I.1 ] 1.78 2.56 <br />1.5 ft. 0.20 0.40 0.85 136 1.94 <br />2.0 ft. 0.17 034 0.70 1.1 I 1.59 <br />2.5 ft. 0.14 0.29 0.60 0.94 1.35 <br />3.0 ft. 0. I2 0.25 0.53 0.82 1.17 <br />4.0 ft 1.0 ft. 0.23 0.46 0.99 L58 2.28 <br />I.5 ft. 0.13 03G 0.76 1.21 1.74 <br />2.0 ft. 0.15 030 0.63 0.99 1.43 <br />2.5 ft. 0.13 0.2G OSd 0.84 1.22 <br />3.0 R. 0.1 l 0 23 0.47 0.73 1.06 <br />*llepth refers to thc dep[h of washed rocA, not depth from surface <br />**Soil textures to be derennined using the results of soil �radation tests and the USDA Texmral Triangle. <br />Gxample: A dispersion trench 3.� feet wide and ? feet dcep, dug in sandy loam soils, for nmoff from a <br />I500 square foot roof, would be 16.65 feet long (chart value of I.I 1 multiplied by IS). <br />3-2-II <br />X/ <br />"J <br />