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Division of Minerals & Geology Colorado Department of Natural Resources 28 May 1996 Page 2 • Haley & Aldrich affected a slope redesign based on a working geologic model of the slope rock mass and instituting an Observational Approach to subsequent slope redevelopment. This work is detailed in site Amendment No. 3. • Amendment No. 4 for the site expanded the North Quarry and changed the possible end use reclamation scenario to include water storage reservoirs which will ultimately benefit the Town of Morrison. This Amendment did not change the approach to slope redevelopment of the East Highwall of the Central Quarry. • Slope redevelopment was progressing within the assumptions and expectations of the established approach through completion of the 1995 Annual Report to DMG and down to the third bench level. • During March of 1996 as the fourth bench and highwall were developed, a localized clay shear feature along foliation was exposed in the fourth highwall. Movement along this feature resulted in a minor rock slope failure extending up to the second bench (top of the slope in the area). This feature revealed new conditions not seen before in the quarry and not included in the earlier geologic model for the subject slope. • Haley & Aldrich investigated the failure using new aerial photography, mapping, test borings, laboratory testing, and analytical and numerical slope stability modeling. Haley & Aldrich subsequently designed and CAMAS/Cooley implemented a slope repair consisting of unloading the top of the failed area by excavation combined with supporting the toe of the failed area with a temporary earthen buttress. • CAMAS/Cooley intends to continue mining down from the fourth bench after removing the temporary earthen buttress used to improve safety during excavation at the top. Slope stability analyses indicate a factor of safety of approximately 1.3 after buttress removal for the current repaired slope configuration. • CAMAS/Cooley intends to monitor the slope via optical survey during subsequent development and has already made plans for an even more conservative slope angle to be constructed if movement is detected. This plan would require encroaching on some, but not all of the current buffer zone. CAMAS/Cooley does not intend to generally extend mining to the proposed new mining limits, but rather intends to create more room within the already permitted acreage to respond to localized instability problems that have or may yet occur in [his part of the quarry. More detailed descriptions and supporting data from investigations and analyses of such occurrences will be provided as part of the facility Annual Reports in the special geotechnical updates