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:y <br />Basic dimensions of the wall were measured at [he time of the final inspection to compare to design <br />dimensions. Wall thickness and height; primary spillway diameter and elevation; emergency spillway <br />elevation, depth and width; and wall base width and thickness were all measured and found to be <br />constructed to specified dimensions as documented in the technical revision. <br />Based on surveying performed after construction (Wilhnore, 1998), the as-built crest elevation (top of the <br />concrete wall) was measured to be approximately El. 6043 feet, 2-feet below the crest elevation shown en <br />the drawings. A check was made for the required volume of sediment and water storage within the pond, <br />and as-built volumes were found to exceed design volumes. Therefore, this discrepancy does not adversely <br />influence pond performance. <br />Steel reinforcement within vertical portion of the concrete sediment pond wall was previously inspected on <br />June 22, 1998. Although some modifications were made to the original design as presented on the <br />drawings noted above, they are considered acceptable. Steel reinforcement in the base of the wall was not <br />inspected because the concrete had been placed before the June 22 inspection. Kiewit personnel (Durben, <br />1998) on site indicated that the steel reinforcement in the base of the wall had been placed as shown oo the <br />drawings. <br />Concrete incorporated into the pond wall was in good condition at the time of final inspection. Two <br />concrete samples were taken during construction. The laboratory compressive strength of these samples <br />met the minimum requirements specified on [he design drawings. <br />As specified on the design drawings, 36 inches of native soil material in the bottom of the pond were to be <br />excavated, and recompacted to obtain a target permeability. Through communication with Kiewit <br />personnel (Landry, 1998), it was found soil samples were not taken for appropriate compaction testing due <br />to rocky soil conditions. And, as a result, compaction specifications could not be met. The native soil was <br />excavated and backfilled in minimum 12-inch lifts with sheeps-foot roller compaction equipment. After <br />constnrction, the permeability of the soil in the pond bottom was tested, and was found to exceed the target <br />permeability. To remedy this, 20 to 30 bags of bentoni[e was used to amend the upper 12 inches of soil <br />within the pond to control seepage. Additional permeability testing was not conducted. Seepage should be <br />monitored while water is present within the pond. <br />Closine <br />I am a Colorado registered Professional Engineer (registration no. 31270), and am thereby qualified to <br />certify the construction of the sediment pond mentioned above. Additionally, I was involved with the eazly <br />stages of engineering design of the sediment pond and West Valley Fill coal mine waste bank. This <br />sediment pond has been constructed according to drawings and specifications included in Technical <br />Revision 29 Phased Mine Expansion, with some field modifications, and to the prudent state of the art. <br />If you have any questions regazding this report, please fell free to contact us at the phone numbers listed <br />below. <br />Sincerely, <br />WESTEC, Inc. <br /> <br />OD ~~G~ <br />='Y <br />o <br />q'°Sl <br />' <br /> ; <br />l <br />, <br />OP k F <br />. <br /> D~ <br />G <br />;~ .~ <br />o:o <br /> '~ 3927A <e <br />Greg Eddy, P.E. <br />Project Engineer <br /> <br />~~~6 ~~jg ; <br />