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application. CRDA -1 has been constructed with three rock underdrains, and construction specifications <br />include 2:1 slopes with 10' wide benches on 30' vertical intervals. The benches are sloped to the inside <br />and graded to drain to perimeter ditches along the sides of the pile. CRDA -2 specifications are similar, <br />with the exception that pile design does not incorporate underdrains, and slope between benches is not to <br />exceed 2.5:1. <br />Stability concerns associated with higher than anticipated water levels in Piezometer CRDA -01 resulted <br />in suspension of waste disposal at the site in 1988, pending drainage modifications and stability re- <br />evaluation. Between 1988 and 1993, the lower three benches were regraded to provide for better slope <br />stability and drainage. Surface drainage was improved by the construction of diversion ditches that allow <br />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 3 0 additional piezometers were installed <br />to evaluate phreatic surfaces and pore pressures. The results of the study showed the pile to be stable as <br />designed. Critical water levels were defined for each of the 30 new piezometers. Based on the study <br />results, the operator was permitted to resume waste disposal at CRDA -1 in 1994. The operator has <br />committed within the permit to monitor the 30 piezometers quarterly, and if water level in any of the <br />piezometers reaches critical target depth as listed on Table 18 -4, stability of the pile will be reevaluated <br />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 at a <br />minimum safety factor of 1.5. The following specific findings apply to the approved refuse disposal <br />areas. <br />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 (4.10.2(1)). <br />Inspection shall occur quarterly and at critical construction periods. A copy of the inspection <br />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 Division <br />finds that such an alternative will ensure the applicable static safety factor, stability of the fill, and <br />protection of the surface and groundwater (4.10.3(5)). No underdrains will be constructed on <br />Cameo Refuse Disposal Areas No. 2. The Roadside Refuse Disposal Area was also constructed <br />without an underdrain. <br />The permittee has demonstrated, based on physical and chemical analyses of refuse material and <br />cover soil, and vegetation field trials, that the revegetation requirements of 4.15 can be met with <br />38 <br />