2019-07-09_REVISION - M2004044 (30)

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Jared Ebert July 8, 2019 Page 11 of 18 Rule 6.4.19, Exhibit S — Permanent Man-made Structures The Division has reviewed the Slope Stability Analysis by Tetra Tech dated November 8, 2018 included within Exhibit 6.5 —Geotechnical Stability Exhibit for the Tucson South Resource 112c permit Resource Conservation Partners, LLC. Page 7 January 10, 2019 amendment application (AM-01). The Applicant will need to address the following adequacy items identified in the review: The following list describes the information used by the Division as presented in the permit amendment application to evaluate slope stability for the proposed site: • Geotechnical boring data is available for the site, but was not provided by the Applicant. o Provided in Exhibit I. • The topsoil and overburden depth ranges from 1 to 10 feet with a typical depth of 3 feet. o Accurate with our modeling. • The aggregate depth ranges from 5 to 46 feet with a typical depth of 23 feet. o Accurate with our modeling. • The aggregate layer contains a 2 to 9-foot-thick mud lens in parts of the site. o Accurate with our modeling. • The depth to bedrock ranges from 5 to 50 feet with an average depth of 27 feet. o Accurate with our modeling. • The stability analysis was limited to the East and West Lakes, since the South Cell will be backfilled to original grade. o Added South Cell slope stability analyses in response to these comments. • A slurry wall will be constructed around the East and West Lakes prior to excavating the areas to create a reservoir. o Accurate with our modeling. • A general 30 feet setback from the top of slope to the proposed permit boundary or man-made structures not owned by the Applicant will be maintained. o Accurate with our modeling. • The South cell mine walls will be mined at the or near the angle of repose, approximately 2H:1 V. o The revised slope stability memorandum includes South Area mine slopes at 2HAV. • The East and West cell mine walls will be mined nearly vertical to a 0.5H:1 V slope. o The revised slope stability memorandum includes analysis for an extended period with a steep highwall at 0.5:1 and concurrent reclamation or limited mining at 3:1. • Groundwater was encountered at depths between 8 and 12 feet below grade during the 2004 drilling program. o Accurate with the report(included with these comments) from 2004. • Monitoring well readings from December 2003 to August 2004 indicated water levels between 4 and 16 feet below grade. o Accurate with the report(included with these comments) from 2004. • The mining cells will be dewatered during aggregate extraction. o Accurate with our models. • The slurry wall will be keyed 6 feet into bedrock. o Accurate with our models. • Residual soil strength parameters were used for the upper 3 feet of weathered bedrock. o Accurate with our models. Aggregate Industries—WCR,Inc 1687 Cole Blvd Suite 300 Golden,CO 80401