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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. <br />Three additional vibrating wire piezometers were installed at CWDA No. 2 in June 2009. These <br />piezometers are designated VWP-06 through VWP-08. All three piezometers were installed in <br />fully grouted boreholes and cables were routed to native ground northeast of the installations <br />for monitoring. Piezometer VWP-06 was installed in one borehole at a depth of 47 feet below <br />the refuse surface at the time of installation. Piezometers VWP-07 and VWP-08 were installed <br />as nested piezometers in another borehole at respective depths of 70 and 35 feet. Approximate <br />instrument elevations (based on survey at the refuse surface) are presented in Table 1. <br />Calibration certificates for the recently installed piezometers are attached. <br />Table 1. Instrumentation Locations <br />Instrument <br />ID Instrument <br />Type <br />North <br />East Elevation' <br />(ft) <br />VWP-01 19351.29 37846.07 6029.4 <br />VWP-02 19307.33 37631.48 6011.4 <br />VWP-03 19307.33 37631.48 6026.4 <br />VWP-04 Vibrating Wire 19287.03 37355.21 6048.4 <br />VWP-05 Piezometer 18993.47 37831.15 5987.5 <br />VWP-06 19633.59 37629.59 6078.6 <br />VWP-07 19482.57 37675.72 6039.9 <br />VWP-08 19482.57 37675.72 6074.9 <br />BG05-04 19094.29 37985.22 6017.9 <br />BG05-05 Inclinometer 18990.85 37823.69 6018.4 <br />BG05-07 18980.11 37493.79 6014.4 <br />Notes: <br />1. Elevation indicated at the instrument for piezometers. Inclinometer <br />elevations were measured at the refuse surface. <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. No pore pressure readings are available at the writing of <br />this report for the recently installed VWP-06, -07, and -08. The measured pore pressures are <br />consistent with the stability evaluation for the coal refuse performed by BGI (2008). <br />Bowie Gob Pile 2 Instrumentation Monitoring 2nd Qtr 2009.doc <br />Project #05-126-GEO <br />Page 2 of 3