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03-10-2000 02~05PM FROM J. E. STOVER 8 RSSOCIRTES TO 2411516 P.02 POWDERHORN COAL COMPANY POND N0.4 • CAMEO NORTH PORTAL CERTIFICATION On December 18, 1991, Larry M. Reschke, PE, certified Pond No. 4 meets or exceeds the design requirements of plans submitted to and approved by the DMG located in Appendix X, Volume 3; Exhibit 21, Volume 5; and appendix WW, Volume 7 of Powderhorn permit application No. C-81-041. The reconfiguration of the permit in 1986 changed the location of the above referenced design information. The pond sizing calculations are presented in Volume 3, Appendix 13-2. A plan view of the pond is presented in Volume 4, Exhibit 88 and a section view is presented in Volume 4, Exhibit 21. The pond was constructed in 1979. The spillway was revised in November and December 1991 to establish separate emergency and primary spillways. On February 11, 2000, during a routine DMG inspection, a sinkhole feature was observed in the bottom of pond 4 immediately adjacent to the inside toe of the pond embankment, directly across from the truck loadout structure. The DMG issued notice of violation (CV-2000-001) for failure to construct or maintain sediment pond to provide adequate capacity to treat run-off and to ensure that embankment remains stable during operational life. The abatement required the excavation and reconstruction of a segment of Pond 4 embankment damaged by piping erosion or otherwise exhibiting evidence of instability and provide construction certification by a qualified registered professional engineer in accordance with Rule 4.05.6(1 D). On February 28, 2000, a 115-foot long segment of Pond 4 embankment was removed and then reconstructed. The fill was placed and spread from the lowest point of the foundation. Materials were spread in layers approximately 72 inches thick and the lifts were made uniformly over the full width of the embankment. Compaction was achieved by wheel rolling with a 980 front end loader with its bucket full of dirt. Compaction was carried to the edge of the }ills so the final slopes are firm. Compaction was tested after the first lull lift and again when the fill was about 4-feet high. Attached compaction tests confirm the 980 loader provided compactive effort adequate to achieve a unit dry weight at least 90% of maximum the unit dry weight attained in a laboratory compaction test in accordance with the specifications of ASTM 7557, Method C, (modified proctor). In accordance with Rule 4.05.6(10), ponds are to be inspected during construction under the supervision of, and certified after construction by, a qualified registered professional engineer. This certification is for the reconstruction of the115-foot long segment of Pond 4 embankment. An enclosed sketch shows the location of the reconstructed embankment. The construction of the embankment was supervised by J. E. Stover, P.E. I have a wide variety experience in the design and construction of earth fill embankments. The embankment was re-constructed on February 28, 2000. To the best of my knowledge and belief the embankment was constructed in accordance with the approved plan and meets the applicable pertormance standards and design criteria with the following exception: The top width of the entire pond embankment does not meet jt~'~~~irement of Rule 4.05.6(11)(h). tai Engineer 3_ io- o 0 Date E~