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indahl & <br />7. ~ tirna:~ of pl~::ant.i.n5.a should be pr'o:~ided. <br />Seeding will occur at the time when ambient <br />temperatur[a and the soil moisture are mast <br />favorable, Exhibit Y. suggests that late fall <br />(November) or late spring (April or May) would <br />be the most likely times. Specific dates <br />within these months would be difficult to give <br />at this time. <br />£3 .. l~u-' fi.ne.l. drainz~ge plan pr-^vided is con.: _•p~:.ually cad~~y~.iate but <br />=some Cuasac infer-ma t. i. on s,'i~ior-rld b~.~ given t^ cii.:rrar.ter•~izr= p.=al.. <br />runoff di.s~.:h:~r-rlf:'s 'Fn these ch~•nnels. <br />No portion of the proposed site is within a <br />100 year fi.ood-plain. The mining application <br />has within it an analysis of existing hydro- <br />logic conditions (Exhibit G) and discusses <br />impacts on the hydrologic regime and conse- <br />quences of mining. A runoff analysis done by ' <br />Rindahl & Associates, Inc. for the 100 year 24 <br />hour precipitation event suggests a peak dis-J' ~1~-1 <br />charge of 146 cubic feet per second for <br />existing site conditions. Because similar <br />soils, slopes and contours will be replaced <br />on the site there is na anticipated increase <br />or decrease in runoff expected. The fallowing <br />calculations and assumptions are provided for <br />reference should another method be used for <br />estimating runoff: <br />Assumptions: <br />Basin area equals 527 acres (0.824 share miles) <br />Basin length - 8800 feet <br />Change in slope (H) 6000 ft. minus 5890 ft. = 110 ft. <br />Slope -- 110 ft. 8800 ft. = 0.0125 <br />Time of concentration (tc) = 0,62 hr. (37 min.) <br />Source: page 26, Soil Conservation Society, Technical <br />Report 55 <br />Velocity <v) 8800 ft. 37 min. x 60 secondsJmin = 4 ft/sec <br />Soil hydrologic group - b <br />Curve number (CN) = 70 (average for site in poor to good <br />range and condition) <br />100 year, 24 hour precipitation event - 5 inches <br />From Applied Hydrology and Sedimentology For <br />Disturbed Lands, B.J. Barfield, R.C. Warner, <br />and C.T. Haan, 1981. On page 66 it is found <br />that a 1 hour, 100 year storm will provide <br />2.25 inches of precipitation (as opposed to <br />the 5 inches that would accumulate over the <br />100 year, 24 hours event). <br />9 <br />& Environmental Servi <br />