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r <br />Mr. Caz1 Mount J " <br />Division of Minerals and Geology <br />1313 Sherman Street, Room 215_ <br />D CI <br />G~~ <br />~p!,p' <br />~-'L ~V. <br />enyer, o orado 80203 <br />RE: " Requested Information for Erosio" n Protection ,~ <br />Acreage Release Request; Holcim (U$) Inc.; Boettcher Mine; M-197'f 349~~ <br />Dear Mr. Mount: <br />-The following information is being submitted on behalf of our client, Holcim ([IS) Inc. <br />for" the Boettcher Mine operation (M-1977-349) located 2 miles north of LaPorte, in <br />Larimei•.County, Colorado. -Holcim (iJS)"Ine.,submitted ati acreage release request in a <br />letter dated August 29, 2005. During your site visit on October 3; 2005, azeas of headcut <br />erosion were identified within the potential release area. This letter and the attached " <br />material,described criteria and methods to be used to stabilize the areas prior to release. <br />The attached sheet illustrates the headcut erosion areas being considered. The sheet <br />"contains a plan view"and cross-section of the designed erosion protection based upori <br />Urban Drainage and Flood Control District (IIDFCD) criteria. Additional design <br />information and assumptions are presented ' in the attached Applegate Group <br />" Memorandum. The UDFCD criteria were used for the design in the absence of available <br />- standard engineering. practices and criteria that would be more applicable to the <br />reclamation land use and potential impacts of the headcut erosion. The UDFCD criteria <br />were established for urban land uses and aze considered conservative to assure "the. <br />protection of urban structures and human safety. -The proposed reclamation land use for <br />the area affected by the headcut erosion is open, Waal rangeland, making the design <br />overly conservative for the application. Therefore, it is proposed that the design included <br />iri the attached materials be used as a guideline for construction of erosion protection <br />aprons with appropriate modifications based on practicle engineering judgemerit. <br />-Peak. flows for the headcut .areas were estimated based on the 10-year -and 100-year <br />recurrence intervals. Flow estimates were then used to design erosion protection for the <br />headcut areas. In general, the design specifies that the headcut area be graded on all sides <br />back to a 4Hi1 V slope and- covered with UDFCD Type I and Type II bedding material <br />prior to the placement of UDFCD Type M riprap (Dso = 12 inches). <br />It is proposed that the headcut erosion areas be graded back to 4H:1 V slopes to reduce the <br />runoff velocity- and erosion. potential of flows entering the drainage gullies below the <br />headcut areas. During grading of the slopes, native material will be left undisturbed as <br />1499 West 720th Avenue, Suite 200 ~ ~ - - _ ~ ~ (303) 452-6677 • Fax (303) 452-2759' <br />Denver, Colorado 80234 2759 wivw.applegategroup.com <br />