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. ~ <br />~/~W C.:7 ^ C~..~ <br />October 6, 1998 <br />Oxbow Mining, Inc. <br />Sanborn Creek Mine <br />P.O. Box 535 <br />Somerset, CO 81434 <br />RE: Construction Certification for Sedimentation Pond C, West Valley Fill <br />Technical Revision 29 <br />Deaz Tom: <br />This letter repots summarizes the fmal inspection of the sediment pond construction for dte new <br />Sedimentation Pond C for the Nest Valley Fill coal mine waste bank. This inspection was held on August <br />24, 1998, with Greg Eddy, P.E. and Don Beesley of Steffen, Robemon and Kirsten (SRK) and Tom <br />Anderson, A.E. of Oxbow Mining, Inc. (Oxbow) present for the inspection. T1te sediment pond was <br />constructed based on designs presented in a report prepazed by Montgomery Watson (1997) titled <br />"Technical Revision 29 Phased Mine Expansion". Applicable design drawings associated with the <br />sediment pond design aze OXW VF•03 and OXW VF-04, presented in TR-29, and prepared by Balaz and <br />Associates (Balaz). The construction contractor for this sediment pond was Kiewit Western, Co (Kiewit). <br />This letter was prepared to satisfy the requirements of Rule 4.D5.6(10) of the RSgulations pf the Colorado <br />Mined Land Reclamation Board for Coal Minin¢ <br />The sediment pond incorporates a reinforced concrete wail to close an erosional feature in a sandstone <br />bedrock outcrop at the toe of the West Valley Fill, a proposed new coal mine waste bank . The bottom of <br />the pond consists of naturally deposited soils, overlain by re-compacted, bentonite amended native soils, <br />overlain by a cobble and boulder protectioe layer. Spillways include an 8-inch diameter steel pipe <br />principal spillway with gate valve, and a 1.5-foot deep trapezoidal emergency spillway at the top of the <br />concrete wall. See Photographs 1, and 2 attached. <br />Conditions at the time of the inspection included pertly sunny skies, with a temperature of approximately <br />80 degrees Fahrenheit. Actions taken for inspection included measuring Boss dimensions of the concrete <br />wall, spillways and pond bottom cobbles. Visual inspection was conducted at the walllra:k connection and <br />of general concrete condition. Pertinent portions of the ahove mentioned technical revision, and the <br />associated drawings and specificarions were reviewed prior to the site visit. Contact was also made with <br />Terry Landry of Kiewit, and Randy Willmore who performed as-built surveying. <br />During the site visit, the walVrock abutment connections were inspected because they were modified from <br />the design drawings based on Feld conditions by Kiewit, and from recommendations included in a letter to <br />Oxbow from WESTEC (now SRK) dated July 15, 1998. Modifications included the addition of a 90 <br />degree bend in the wall (on the east abutment) to make an acceptable connection with the rock outcrop (se--~ <br />Photo 3). Additionally, on the east abutment, the wall is founded an some portions of sandstone bedrock <br />that may become unstable. To remedy this, rock bolts were installed to provide additional stability (see <br />Photo 4). <br />5600 SUUth 9uebBC Streat, Suite :507-D Englewood. olorado 80111 Ph. 303 290 9113 fax ;~:, <br />Rero Vdinnemucca Elko Fort Collins Tucson t. ~. <br />Nevoda tdovada Mevaoa Colorado G,riipnq G <br />