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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 on the attached site plan. Since <br />installation two of the vibrating wire piezometers have stopped working correctly (VWP-01 and <br />VWP-04). Diagnostic tests indicate that shorts have developed, likely due to damaged cables. <br />Three additional vibrating wire piezometers, designated VWP-06 through VWP-08, were <br />installed at CWDA No. 2 in June 2009 to supplement the remaining piezometers. Completion <br />details of these piezometers are described by BGI (2009). <br />Pore pressures measured to date are presented on the attached figure. Pore pressures have <br />remained relatively steady for piezometers VWP-02, -03, -05, and -06. However, pore <br />pressures at VWP-07 and -08 have increased sharply since installation in June 2009. The <br />increase in pore pressure is attributed to refuse placement in the area of these piezometers <br />coupled with slow drainage due to the relatively low hydraulic conductivity of the compacted <br />refuse. Approximately 30 feet of coal refuse has been placed in the area of VWP-07 and -08 <br />over the past six months. The measured pore pressures are still well below the pore pressures <br />at failure for similar confining pressures for the CU triaxial shear tests that have been conducted <br />as part of the on-going stability evaluation for this refuse bank. <br />Pore pressures will continue to rise if the rate of refuse placement continues at or above the <br />current rates and is concentrated in one area. Pore pressures are anticipated to decrease as <br />drainage occurs. In any event, on-going monitoring of all piezometers is recommended to <br />monitor pore pressure responses to the on-going refuse placement. Otherwise, the measured <br />pore pressures are consistent with the revised stability evaluation for the coal refuse performed <br />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 />owie Gob Pile 2 Instrumentation Monitoring 4th Qtr 2009.doc <br />Project #05-126-GEO <br />Page 2 of 3