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STATE OF COLORADO <br />COLORADO GEOLOGICAL SURVEY- serving the people of Colorado <br />Department of Natural Resources <br />1313 Sherman Street, Room 715 <br />Denver, CO 80203 <br />Phone: (303) 866-2611 <br />Fax: (303) 866-2461 <br />DATE: June 18, 2010 <br />TO: Berhan Keffelew, Tony Waldron, David Berry <br />FROM: TC Wait, Jon White <br />SUBJECT: CGS assessment of a May 2010 Technical Revision of the <br />Pikeview Quarry Mine Plan (M-77-211, TR15) <br />COLORADO <br />piwo trli'7 t' T, <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Bill Ritter, Jr. <br />Governor <br />Vincent Matthews <br />Division Director and <br />State Geologist <br />Mike King <br />Executive Director <br />At the request of the Colorado Division of Reclamation, Mining, and Safety (DRMS) the Colorado Geological Survey <br />(CGS) is providing this review of a proposed May 2010 Technical Revision to the Pikeview Quarry mine plan. This is <br />the second technical review to the mine plan CGS has reviewed following a large rockslide in December 2008, the <br />subsequent reactivation and enlarging of the rockslide in September 2009 (Figure 1), continued monitoring <br />movement and instability in the quarry face, and attempt to remove portions of the South Block by blasting. The <br />purpose of the TR15 mine plan revision is to permit the mine operator to 1) backfill material in the north end of Area <br />H to try to stabilize the toe of the slide, 2) blasting to remove unstable rock blocks (north and south blocks), and 3) lay <br />back the southern end of the quarry to a more gradual slope. <br />Figure 1. Pikeview quarry rockslide after September 2009 reactivation (shown in red shading). <br />Dashed red line is the headscarp. Annotations are informal names of features referred to in this letter.