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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). Due to damage to existing vibrating <br />wire piezometers, an additional two VWP's (VWP -9 and VWP -10) were installed on May 18, <br />2012. During the June 19, 2013 site visit we were able to extract information at installations <br />VWP -06, 08, 09 and 10, which provides good lateral representation of the coal waste in CDWA <br />No. 2. We received an error message at VWP -05 which was corrected and that station was <br />successfully read on June 22, 2013 during our weekly site visit. <br />Pore pressures measured to date are presented on the attached figure. Pore pressures at VWP - <br />06, VWP -08. VWP -09 and VWP -10 were constant during the 1st quarter of 2013. Those reading <br />are consistent with little or no new gob material at those sites and the readings indicate <br />generally stable conditions at those piezometer sites. Readings at these piezometers have <br />generally decreased since they were installed. This is a good indication that internal drainage is <br />occurring and that waste material is dewatering due to consolidation and trending towards <br />equilibrium. 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 the on- <br />going stability evaluation for this refuse bank. Readings at VWP -05 decreased slightly indicated <br />pore pressure relief as the pile dewatered. <br />Pore pressures are anticipated to continue to decrease as drainage occurs. In any event, on- <br />going monitoring of all piezometers is recommended to monitor pore pressure responses to the <br />on -going refuse placement. Otherwise, the measured pore pressures are consistent with the <br />revised stability evaluation for the coal refuse performed by BGI (2008). <br />Site Visit Observations <br />During my site visit on June 19, 2013 with you and Ms. Tamme Bishop of J.E. Stover & <br />Associates, I noted the following items of interest to monitor as compaction and grading <br />operations at CWDA No. 2 continue; <br />1. Several wet areas were noted near the toes of the slope at the intersection with haul <br />roads that cross the slope. These are normal and anticipated as the gob dewaters. In <br />general, the locations are small and appear to dry out quickly leaving a white residue on <br />the surface of the pile to indicate their locations. No water was observed to be flowing <br />from any of these locations and no movement of the slopes as a result of these <br />dewatering spots was observed. These spots should be monitored periodically for any <br />change in conditions, slumping, excessive flows, etc. As indicated by the VWP results, <br />the pore pressures continue to drop or remain constant as the gob dewaters over time. <br />2nd Qtr Monitoring Report.doc PN #05- 126-GEO <br />Page 2 of 4 <br />