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• • III IIIIIIIIIIIIIIII ~ <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY ~ of cow <br />Department of Natural Resources ~¢, .~ <br />°.:, o, <br />1313 Sherman St., Room 21 S . %y I~^_11;; • <br />Denver, CO 80203 ~~ <br />Phone: 1303) 866.7567 raic • <br />FAX: (3031 872-8106 <br />Roy Romer <br />Governor <br />nt¢hael B. Long <br />Divrsion Direcmr <br />October 22,1992 <br />To: Steve Shuey ~r1 <br />From: David Berry'- <br />Re: Somerset Mine-Refuse Pile Diversion Ditch-C-81-022 <br />I have reviewed the refuse pile diversion ditch calculations <br />provided with the Somerset Mine Midterm Response Technical Revision <br />application. The ditch designs and culvert designs are adequate. <br />Stover has probably overestimated the contributing drainage area by <br />over 40 acres; perhaps as much as 50 acres. My calculation for <br />peak flow used a drainage area of 16 acres, and a curve number of <br />63. I believe the higher curve number is more appropriate than the <br />curve number of 58 used by Stover. Using these numbers my peak <br />flow result is approximately 5.5 cubic feet per second. Using more <br />coservative assumptions a peak discharge of 13.14 was obtained, <br />which compares well with Stover's result of 12.87. <br />The ditch and culvert calculations provided will pass the 12.87 <br />peak discharge, which as I stated before, is probably an <br />overestimation of the expected 100 year, 24 hour peak flow. <br />I therefore recommend approval of the provided ditch designs at <br />this time. As dicussed, you may approve this specific section of <br />the Technical Revision application as a separate Minor Revision. <br />