2019-07-09_REVISION - M2004044 (30)

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Jared Ebert July 8,2019 Page 12 of 18 • A mud lens was modeled in each critical cross-section in a similar evaluation completed for the Tucson South mine in November 2004. o The mud lens has been modeled in cross sections where found during geotechnical investigations for all previous and current slope stability analyses. • A mud lens was not modeled in each cross-section in the 2018 Tetra Tech report. o Accurate with our models. • A 500 psf load was applied to Tucson Road and Hwy 7 cross-sections to simulate traffic. o Accurate with our models. • A 3,000 psf load was modeled to simulate the weight of the oil and gas well. o Accurate with our models. • The material properties used were the same as those required for the 2004 analysis based on a memo from Allen Sorenson dated August 29, 2004. o Accurate with our models with the addition of material properties for a reclamation slope that was not used in previous models. • Laboratory strength tests were not performed on the site soils. o Accurate. • The groundwater elevation was modeled at the base of the pit on the pit side of the slurry wall. o Accurate. • A horizontal acceleration of 0.067g was used for the seismic models. o Accurate. • The minimum factor of safety for static analysis is 1.5 o Accurate. • The minimum factor of safety for seismic analysis is 1.3 o Accurate. The following information is required by the Division to continue the stability analysis review. 33. On Page D-4 of the Mining Plan, the Applicant states the perimeter setbacks from the permit boundary are shown on Exhibit C — Mining Map. Please update the Exhibit C Maps to indicate the numerical offset distance for the perimeter setbacks from the permit boundary. Due to the number of third-party structures in the vicinity of the mine, dimensioning all setbacks was impractical. A table showing the minimum required offset distance and actual setback distance for third party structures was included on Exhibits C-2 and C-3. 34. In Section 2.0 Geology of the Tetra Tech report, the Applicant states 130 boreholes have been drilled on the site. Please provide the geotechnical borehole data and location map for Division review. The borehole data was provided in the application in Exhibit I. 35. On Page 3 of the Tetra Tech report, the Applicant states the water table was assumed at 15.5 feet below grade on the south side of the slurry wall. The Division anticipates the groundwater elevation would be elevated due to mounding effects on the south side of the slurry wall. Please provide justification for the modeled groundwater depth for the Highway 7 cross-section. The slope stability model was updated with the phreatic surface approximately 10 feet below the ground surface near the top of the sand and gravel layer. Aggregate Industries—WCR,Inc 1687 Cole Blvd Suite 300 Golden,CO 80401