Laserfiche WebLink
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 l <br />Phone: (303) 866-2611 <br />Fax: (303) 866-2461 <br />DATE: September 10, 2009 <br />TO: Berhan Keffelew, Tony Waldron, David Berry <br />COLORADO <br />i PFF, 7-r, <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />FROM: Jon White, TC Wait Bill Ritter, Jr. <br />Governor <br />SUBJECT: Review of Slope Stability Evaluation, Pike View Quarry Harris D. Sherman <br />Executive Director <br />Vincent Matthews <br />Division Director and <br />State Geologist <br />At the request of the Colorado Division of Reclamation, Mining, and Safety (DRMS) the <br />Colorado Geological Survey (CGS) has conducted a technical review of the Slope Stability <br />Evaluation for the Pike View Quarry (5/19/09) by CTL/Thompson. This stability evaluation was <br />initiated by Castle Concrete following a rockslide that occurred the morning of December 2, <br />2008. The CGS also conducted a site inspection of the quarry rockslide and provided an initial <br />assessment to DRMS in a letter memorandum dated January 7, 2009. <br />The purpose of this technical review is to provide comment to DRMS concerning the substance, <br />conclusions, and implications of the CTL report pertaining to the cause of the slide, the ongoing <br />hazards, and proposed mitigation strategies. <br />General Comments on the CTL Report: <br />The scope of the CTL report was primarily to evaluate the stability of the existing slide mass. <br />The report does not include 1) any analysis of the dangerous blocks above defined by the <br />incipient scarps and tension cracks, 2) forensic work to determine the cause of the slide, and 3) <br />offer any specifics into proposed mitigation work. <br />The CTL report does not cite the recent geologic mapping by Morgan and others (2003) or the <br />MSHA memo concerning the Pikeview Quarry slope stability evaluation by Jerry Davidson <br />(9/17/86). <br />The full extents of the tension cracks observed by CGS above the north part of the landslide are <br />not shown on figure 4 (geologic map) of the CTL report. <br />The CTL report seems to have a concerted bias towards clay seams in the rock-mass (that they <br />attribute to formational bedding) and groundwater as the main causal agents in the slope failure.