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Vibrating Wire Piezometers <br />Five vibrating wire piezometers, designated VWP-01 through VWP-05, were installed in gob at <br />Gob Pile No. 2 in June 2005. The piezometers were grouted in drilled boreholes as described <br />by Buckhorn Geotech (2006). Piezometer locations are presented on the attached site plan. <br />Since installation two of the vibrating wire piezometers have stopped working correctly (VWP-01 <br />and VWP-04). Diagnostic tests indicate that shorts have developed, likely due to damaged <br />cables. <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. The observed pore pressures <br />continue to dissipate in VWP-03, while pore pressures measured at VWP-02 and VWP-05 remain <br />relatively stable. The measured pore pressures are consistent with the stability evaluation for <br />the coal refuse performed by Buckhorn Geotech, Inc. (2008). <br />References <br />Buckhorn Geotech, Inc. (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. (2008). "Revised Stability Evaluations for Coal Mine Waste Disposal <br />Area No. 2, Bowie No. 2 Mine, DRMS Permit C-1996-083 Delta County, Colorado", <br />September 22, 2008. <br />Closing <br />On-going monitoring of inclinometers and piezometers at Gob Pile No. 2 provides an indication <br />of the stability of Gob Pile No. 2 as well as an indication of probable performance for other gob <br />piles at Bowie. For these reasons, we recommend continued monitoring of this instrumentation <br />on a quarterly basis. We sincerely appreciate the opportunity to work with you on this project. <br />If you have any questions regarding this letter or the instrumentation monitoring at Gob Pile <br />No. 2, please let us know. <br />Sincerely, <br />SUCKHORN GEOTECH, INC. <br />I <br />Brett R. Byler, P.E. <br />Enclosures: Site Plan, Inclinometer Cumulative Displacements, Summary of Pore Pressure Monitoring <br />cc: Jim Stover, J.E. Stover and Associates <br />Bowie Gob Pile 2 Instrumentation Monitoring Dec 2008.doc <br />Project #05-126-GEO <br />Page 2 of 2