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CIVIL RES~URCES,LLC <br />ENGIN EENB 6a PLgNNEPB <br />March 31, 2006 <br />Ms. Erica Crosby <br />Division of Minerals and Geology <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />RE: Hall•Irwin Corporation, Application No. M-2006.003 <br />Parker/Dersham Sand and Gravel Resource; March 13, 2006 Adequacy Review <br />Dear Ms. Crosby: <br />Below is our response to question 33 of your adequacy review comment: It appears that the <br />ParkerlDersham site is within the 100-year floodplain of the South Platte River. Please provide <br />the flood elevations(s) to be expected under a "worst case" Flooding scenario and specific <br />mitigation measures that will be implemented to minimize the potential for any offsite impacts. <br />Legible copies of the Flood;lnsuran'ce Rate Maps ("FIRM")through the mine reach would <br />facilitate the Divisjonts review. <br />The site is witHinthe effective.100-yeac,floodplain currently recognized by FEMA. Refer to the attached <br />FIRM. Flood elevations~range from 4944_feet to 4948-feeYabove`mean'ssea level ba$ed orrUSGS <br />mapping.`This 8quates;to approximately zero to-two feet of,flood:.depth on average over the site. Flow <br />velocities`in thisshallow fipoding area would be in the range of 0 to two feet pee secohd and not pose <br />an erosion.risk,, Therefore, specific mitigationrmeasures to prevent downstream impacts,duringthe <br />100-year flood event=a_re ndtnecessary. <br />Please contact me if yoU have any questions. <br />Sincerely, <br />CIVIL RESOURCES, LLC <br />/~~~~~ <br />Brad L. Hagen, P.E. <br />Civil EngineedPrincipai <br />J:1HaIIlnvinlParker-DershamlDMGlAdequacy Review il0oodplainlFlood response 33.doc <br />451 OqK SrREET. SuiTE 2~9 ~ P. O. Box 660 ~ FaEO eaicK, CO 8053 ~ 1303) 833-141 6 ~ 13031 933.2850 -Fax <br />