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Vibrating Wire Piezometers <br />Five vibrating wire piezometers, designated VWP -01 through VWP -05, were installed in <br />coal refuse at CWDA No. 2 in June 2005. The piezometers were grouted in drilled <br />boreholes as described by BGI (2006). Piezometer locations are presented on the <br />attached Instrumentation Site Plan. Since installation a total of five vibrating wire <br />piezometers have stopped working correctly (VWP -01, VWP -02, VWP -03, VWP -04 and <br />VWP -07). The first two VWP's were damaged and went out of service between June and <br />August 2005. VWP's 03 and 04 had apparent damage and gave spurious readings on <br />June 15, 2011 and were not read after that date. Diagnostic tests on the damaged VWP's <br />indicate that shorts have developed, likely due to damaged cables. Three additional <br />vibrating wire piezometers, designated VWP -06 through VWP -08, were installed at CWDA <br />No. 2 in June 2009 to supplement the remaining piezometers. VWP -07 went out of <br />service between March and June 2011. Completion details of these piezometers are <br />described by BGI (2009). Due to damage to existing vibrating wire piezometers, an <br />additional two VWP's (VWP -9 and VWP -10) were installed on May 18, 2012. During the <br />March 17, 2014 site visit we were able to extract information at installations VWP -05, 06, <br />08, 09 and 10, which provides good lateral representation of the coal waste in CDWA No. <br />2. <br />Pore pressures measured to date are presented on the attached Pore Plat figure. Pore <br />pressures at all recording piezometers decreased during the 15t quarter of 2014 from the <br />4t" quarter 2013 readings. This is a good indication that internal drainage is occurring and <br />that waste material is dewatering due to consolidation and trending towards equilibrium. <br />All measured pore pressures are well below the pore pressures at failure for similar <br />confining pressures for the CU triaxial shear tests that have been conducted as part of <br />the on -going stability evaluation for CDWA No. 2. Table 1 summarizes the individual pore <br />pressures since installation and since their last readings for the currently active VWP's. <br />Table 1. SummaEy of Active VWP Pore Pressures <br />VWP ID <br /># <br />Initial Pore <br />Pressure <br />(psi) <br />12/17/13 <br />Pore <br />Pressure <br />si <br />3/17/14 <br />Pore <br />Pressure <br />(psi) <br />Difference <br />Since <br />Installation <br />(psi) <br />Difference <br />Since Last <br />Reading <br />(psi) <br />VWP -05 <br />6.8 <br />2.5 <br />2.0 <br />-4.8 <br />-0.5 <br />VWP -06 <br />11.3 <br />15.2 <br />14.8 <br />+3.5 <br />-0.4 <br />VWP -08 <br />12.2 <br />13.4 <br />12.6 <br />+0.4 <br />-0.8 <br />VWP -09 <br />1.5 1 <br />1.6 <br />1.4 <br />-0.1 <br />-0.2 <br />VWP -10 <br />0.6 <br />0.7 <br />0.5 <br />-0.1 <br />-0.2 <br />Discussion of Individual Active VWP's <br />VWP -05: Installed on August 3, 2005, VWP is installed near the toe of the CDWA #2 <br />pile adjacent to the access road/bench. This VWP monitoring indicated a decline in pore <br />pressure from an initial value of 6.8 psi to the March 2006 reading of 3.5 psi. The <br />2014- 1st Quarter Monitoring Report PN #05- 126 -GE0 <br />April 2, 2014 <br />Page 2 of 6 <br />