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Vibrating Wire Piezometers <br />Five vibrating wire piezometers, designated VWP-01 through VWP-05, were installed in coal <br />refuse at CWDA No. 2 in June 2005. The piezometers were grouted in drilled boreholes as <br />described by BGI (2006). Piezometer locations are presented in Table 1 and on the attached <br />site plan. Since installation two of the vibrating wire piezometers have stopped working <br />correctly (VWP-01 and VWP-04). Diagnostic tests indicate that shorts have developed, likely <br />due to damaged cables. Three additional vibrating wire piezometers, designated VWP-06 <br />through VWP-08, were installed at CWDA No. 2 in June 2009 to supplement the remaining <br />piezometers. Completion details of these piezometers are described by BGI (2009). <br />Pore pressures measured to date are presented on the attached figure. The initial high <br />readings and sudden decrease in pore pressure is due to curing of the grout after installation. <br />In general, pore pressures were observed to rise after the grout cured. The pore pressure is <br />attributed to increased loading due to gob placement coupled with slow drainage due to the <br />relatively low hydraulic conductivity of the compacted gob. Subsequent pore pressure decrease <br />is attributed to drainage. The measured pore pressures have remained relatively stable for <br />piezometers VWP-02, -03, and -05. Pore pressures for piezometers VWP-06 through VWP-08 <br />range from approximately 11 to 15 psi. Although these pore pressures are slightly greater than <br />the highest recorded pressures from the other piezometers over the monitoring period, they are <br />well below pore pressures that were measured during the CU triaxial shear tests at failure <br />condition for similar confining stresses as the piezometers. On-going monitoring of all <br />piezometers is recommended to monitor pore pressure responses to the on-going refuse <br />placement. Otherwise, the measured pore pressures are consistent with the revised stability <br />evaluation for the coal refuse performed by BGI (2008). <br />References <br />Buckhorn Geotech, Inc. (BGI), 2006. "Geotechnical Report, Stability Evaluation of Coal Waste <br />Disposal Area, Bowie No. 2 Mine, Delta County, Colorado", February 15, 2006. <br />Buckhorn Geotech, Inc. (BGI), 2008. "Revised Stability Evaluations for Coal Mine Waste <br />Disposal Area No. 2, Bowie No. 2 Mine, DRMS Permit C-1996-083 Delta County, <br />Colorado", September 22, 2008. <br />Buckhorn Geotech, Inc. (BGI), 2009. "Summary of Instrumentation Monitoring, 2nd Quarter <br />2009, Bowie Coal Waste Disposal Area No. 2", letter to Bowie Resources, LLC dated <br />June 17, 2009. <br />Bowie Gob Pile 2 Instrumentation Monitoring 3rd Qtr 2009.doc <br />Project #05-126-GEO <br />Page 2 of 3