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benches was conducted in the spring of 2002. <br />Geotechnical analyses for CRDA -1, and CRDA -2, are provided in Appendices 13 -4 and 13 -5 of the <br />application. CRDA -1 has been constructed with three rock underdrains, and construction <br />specifications include 2:1 slopes with 10' wide benches on 30' vertical intervals. The benches are <br />sloped to the inside and graded to drain to perimeter ditches along the sides of the pile. CRDA -2 <br />specifications are similar, with the exception that pile design does not incorporate underdrains, and <br />slope between benches is not to exceed 2.5:1. <br />Stability concerns associated with higher than anticipated water levels in Piezometer CRDA -01 <br />resulted in suspension of waste disposal at the site in 1988, pending drainage modifications and <br />stability re- evaluation. Between 1988 and 1993, the lower three benches were regraded to provide for <br />better slope stability and drainage. Surface drainage was improved by the construction of diversion <br />ditches that allow surface runoff to exit around the pile instead of contacting the face. <br />A stability evaluation was performed in the spring of 1994 by Western Engineers, Inc. As a part of the <br />study, pump testing was conducted in existing piezometers and 30 additional piezometers were <br />installed to evaluate phreatic surfaces and pore pressures. The results of the study showed the pile to <br />be stable as designed. Critical water levels were defined for each of the 30 new piezometers. Based <br />on the study results, the operator was permitted to resume waste disposal at CRDA -1 in 1994. The <br />operator has committed within the permit to monitor the 30 piezometers quarterly, and if water level in <br />any of the piezometers reaches critical target depth as listed on Table 18 -4, stability of the pile will be <br />reevaluated and corrective action taken if necessary. <br />CRDA -1, and 2 will be monitored throughout construction. Monitoring will include: <br />1. Piezometric monitoring of the coal processing waste embankment; <br />2. Monitoring of side slopes to maintain a maximum slope angle of 2:1 between benches on <br />CRDA -1, and 2.5:1 on CRDA -2; <br />3. Monitoring compaction of constructed lifts; and <br />4. Quarterly inspection for stability and compliance with approved plan by a registered <br />professional engineer. <br />Geotechnical analyses included in the permit application show that CRDA -1 and CRDA -2 are stable <br />at a minimum safety factor of 1.5. The following specific findings apply to the approved refuse <br />disposal areas. <br />1. The disposal area will be inspected on a regular basis by a qualified professional specialist under <br />the direction of the professional engineer, experienced in construction of similar earth and waste <br />structures. Inspection by this person has been approved by the Division as appropriate <br />(4.10.2(1)). Inspection shall occur quarterly and at critical construction periods. A copy of the <br />inspection report will be retained at the mine office and a copy will be forwarded to the Division. <br />2. An alternative subdrainage system for the coal mine waste area has been approved. The <br />Division finds that such an alternative will ensure the applicable static safety factor, stability of <br />the fill, and protection of the surface and groundwater (4.10.3(5)). No underdrains will be <br />constructed on Cameo Refuse Disposal Areas No. 2. The Roadside Refuse Disposal Area was <br />also constructed without an underdrain. <br />Permit Revision No. 5 38 July 10, 2012 <br />