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• <br />APPENDIX D <br />March 2000 -3- 993-2099.150 <br />specific areas has been taken into account in the exploratory investigation and remediation <br />programs. <br />2.3 Rock Quality <br />The bedrock within the Phase IV area primarily consists of Cripple Creek Lapilli Breccia. <br />The immediate 3 to 6 feet of bedrock beneath the surficial soils is often quite fractured and <br />moderately weathered. The bedrock beneath this is strong and competent with only limited <br />evidence of weathering. Joints are widely spaced (typically in excess of 1 to 3 feet <br />spacing), and generally steeply dipping. The joints are also relatively planar but quite <br />rough with a high frictional strength. The resulting rock mass is essentially an assemblage <br />of large sized interlocking blocks that are massive and of good to very good rock quality. <br />The strength of the rock is sufficiently high that stress fracturing would not occur even in <br />• the deep workings. <br /> <br />According to core samples from the Main Cresson Mine (see Amendment No. 7, <br />Volume 4, Appendix 4), the Cripple Creek Lapilli Breccia has an unconfined strength <br />ranging from approximately 11,000 to 27,000 pounds per square inch (psi). Based on the <br />rock strength and degree of jointing, the bedrock within the Phase IV area would have a <br />Rock Mass Rating (RMR, Bieniawski 1989) ranging between 60 to 70, which is considered <br />as good quality rock. <br />The veins that were mined in the Phase IV area are generally aligned in a north-south <br />orientation, which is reflected in the underground working alignment shown on Drawing <br />Nos. 1 and 2. The underground workings indicate that the veins are steeply dipping <br />(approximately 75 degrees). <br />I:%9%20991FML REPORT2099APPD.DW Golder Associates