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-6- a. The application text (Section 2.05.3(4)) provides runoff volume numbers which are different from the numbers provided by the Applied Hydrology Associates. 'For example, the text indicates that the 10 year, 24~hour and 100 year, 24 hour runoff volumes are 2.52 acre-feet and 5.89-acre feet, respectively. 11be_ Applied Hydrology Associates figures are~2 acre-feet and 7.44 acre-feet C~fj for the 10 year, 24 hour and 100 year, 24 hour storms, respectively. Some of the difference is explained by the fact that different acreage values were used, but even with this factor, a large difference exists. The Applied Hydrology Associates figures are reasonable and may be used. b. The USLE calculations contained in Section 2.05.3(4) are also different from those contained in the PHC Section. The ~~,,5- 2.05.3(4) section indicates a three year sediment yield of 0.3 acre-feet (based on a value of 6.64 tons per acre per year). (I:' The Applied Hydrology Associates provided a value of 68.8 tons per acre, but the time period is not specified. However, if their equation variables are multiplied, the value is 24.08 tons per acre per year. Neither of the values are accurate. The Section 2.05.3(4) derivation incorrectly uses the K, LS and CP variables. The SCS.K ~~ value for the local soil is .37, not .26. The LS factor for theme site is much higher than the .3 value used; C factor cannot exceed 1.0 (1.67 is used). In general a combined CP factor of 1.0 is used \- for disturbed areas. yb The Applied Hydrology Associates value is also based on variables which are suspect. Their use of an R factor of 40 is incorrect, •' it should be 80 to 85. Also, the LS factor of 7.4 is probably too ~` small. Division sediment yield calculations are higher than both C" values provided and I recommend that the 0.1 acre-foot/disturbed acre rule be used. This would allow for three acre-feet of storage. If the operator chooses to substantiate a smaller sediment yield ~ value, then a revised USLE application must be used. The R value should be about 80; the K factor about .37 to 43; and the CP factor ~ 1.0. The LS factor is a key variable. Division measurements of U ~4ap (Exhibit) KK indicate average slopes which are about 25% and slope lengths which vary from about 150 feet to 400 feet. These numbers indicate a much higher LS value than has been used previously. It is possible that the applicant is projecting disturbed area configurations to achieve the lower LS factors used, but this remains to be substantiated. c. The pond designs are not adequately detailed to conduct a proper evaluation. For example, the cross section is not specifically correlated to the plan view diagram, and contour information is not provided with the plan view.