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S 35715 HIGHWAY 40 <br /> BUILDING B, SUITE 120 <br /> A L B E R T F R E T & S 0 N S EVERGREEN, CO 80439 <br /> MAIN: (303) 289-1837 <br /> September 28, 2021 <br /> Email to netenhays(aWate.co.its <br /> Division of Reclamation, Mining and Safety <br /> c/o Peter Hays <br /> 1313 Sherman Street, Room 215 <br /> Denver, CO 80203 <br /> Re: AFS Response to Walstrumn Quarry M-1983-033 AM-09 Geotechnical Review #2 <br /> Dear Peter: <br /> Below please find the AFS response to Zach Trujillo's September 17, 2021 additional comment on <br /> Geotechnical Stability Exhibit. This response was prepared with input from Tetra Tech's engineers. <br /> DRMS Geotech Comment: <br /> Under Section 1.0 of the Exhibit, discussion regarding the potential of natural geologic hazards within the Spur <br /> Amendment is mentioned along with mitigation options downslope. However, this discussion appears to be <br /> specific to areas within the pit and not along the undisturbed outslopes of the spur area. Please include the <br /> following comments with the Division's review for the Walstrum AM-09: <br /> • Please provide additional details regarding if there are potential natural geologic hazards along the <br /> undisturbed outslopes of the proposed spur area along with any mitigation options if applicable. <br /> • Additionally,please address the potential for rockfall along the undisturbed outslopes above the Highway <br /> 6 and Clear Creek corridor due to blasting and any mitigation options if applicable. <br /> AFS Response: <br /> "Rockfall is a significant natural hazard that affects the highway system. There are over 750 locations <br /> statewide recognized as having chronic rockfall hazards. It is important to recognize that rockfall is <br /> sporadic and unpredictable. Rockfall can occur at any time from almost any location along a slope. The <br /> purpose of implementing rockfall mitigation is to reduce the risk of rockfall at a specific location. " ' <br /> Potential natural geologic hazards in Clear Creek Canyon from Idaho Springs to Golden include rockfall <br /> along the relatively short distance of canyon in which the proposed Spur Amendment is located. The <br /> potential for rockfall exists on the steep slopes of the canyon (Geologic Hazards in East-Central Clear <br /> Creek County, Colorado by Mark S. Pelizza [1978] and Attachment 10 in Response to Adequacy Review <br /> #1 [August 17, 2021]). Rockfall occurs through the continuous natural weathering of rocks as visible in <br /> the canyon especially after heavy rain and ice and snowmelt events. To address this potential, the <br /> Colorado Department of Transportation(CDOT)periodically performs rockfall mitigation work <br /> throughout the canyon including adjacent to the Existing Quarry and the Spur Amendment area in <br /> cooperation with AFS; this coordination will continue. <br /> Page 1 of 3 <br />