Laserfiche WebLink
D. A. Berry - 9 - December 4, 1996 <br />93. DMG -Upon brief review of the curve number analyses provided in the above-referenced <br />application, I note that the Mountain Shrub areas are represented by a Curve Number of <br />41, which produces zero modeled runo„~ I acknowledge the detailed rrgetadon data <br />provided in Exhibit S; however, I am concerned that Lire assumption of zero runoff may <br />be too risky. Are you sure that the Curve Number of 41 appropriately represents all of <br />the areas for which it has been applied? Please provide a discussion regarding the <br />appropriateness of such a low Cusve Number. <br />BRL -The vegetation areas sampled were sampled due to their proximity to the disturbed <br />area. The vegetation types delineated in the sub~rainage areas, not used for vegetation <br />sampling, are visually the same as the vegetation types delineated in the sub-drainage areas <br />that were used for sampling. It is not unreasonable to assume that like vegetation types <br />within such a small drainage area would exhibit similar curve number values. During a <br />recent sigtriScant precipitation event, lower draws A through D were visited to see if a <br />water sample could be obtained. There was no run-off from any of the drainages even <br />thought it had been raining off and on for a couple of days and the ground was saturated. <br />This sampling was performed on September 6, 1996 and is documented on the appropriate <br />monitoring sheets. I believe this lack of surface run-off helps establish a certain comfort <br />level with the low curve number. Additionally, it is the disturbed areas on the mine sites <br />which generate most of the run-off. There is such an large difference between run-off <br />volume from disturbed and undisturbed areas that the run-off from the undisturbed areas is <br />often inwnsequential. <br />Please call if you have any questions. <br />Sincerely, <br />~"~ -~ <br />Jim Stover, P.E. <br />Consulting Engineer <br />