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CWDA No. 3 <br />#01349-0001 <br />01/08/18 <br />X:\2008 ALL PROJECTS\01349 -Bowie Resources, LLC\01349-0001 Bowie Mine REVISED\200 - Geo\Gob 3\Instrumentation Monitoring\2017\01349-0001 GP3 4thQ2017 010818.doc 2 <br />Discussion of Vibrating Wire Piezometers <br /> <br />VWP -A Deep <br />VWP-A Deep was installed on October 6, 2014 near the northern edge of CWDA No. 3. VWP- <br />A Deep was installed in the foundation soil approximately eight feet below the bottom of the <br />gob. The pore pressures recorded at VWP-A Deep generally decreased since installation until <br />September 2015. After that, the pore pressures have fluctuated within a narrow range. In <br />general, HBET does not believe that the pore pressure changes in VWP-A Deep are cause for <br />concern regarding stability of the gob pile. <br /> <br />VWP -A Shallow <br />VWP-A Shallow was installed on October 6, 2014 near the northern edge of CWDA No. 3. <br />VWP-A Shallow was installed approximately ten feet above the base of the gob. After <br />installation, the pore pressures dropped until November 2014. Between November 2014 and <br />September 2015, increases in the pore pressures were recorded at VWP-A Shallow. However, <br />between September 2015 and December 2016, the pore pressures decreased. Since then, the data <br />have fluctuated within a narrow range. In general, HBET does not believe that the pore pressure <br />changes in VWP-A Shallow are an indication of instability in CWDA No. 3. <br /> <br />VWP -B Deep <br />VWP-B Deep was installed on October 6, 2014 in the west-central portion of CWDA No. 3. <br />VWP-B Deep was installed in the foundation soil approximately ten feet below the bottom of the <br />gob. Since installation, the pore pressures recorded at VWP-B Deep have fluctuated within a <br />narrow range. In general, HBET does not believe that the pore pressure changes in VWP-B <br />Deep are an indication of instability in CWDA No. 3. <br /> <br />VWP -B Shallow <br />VWP-B Shallow was installed on October 6, 2014 in the west-central portion of CWDA No. 3. <br />VWP-B Shallow was installed approximately ten feet above the base of the gob. Since <br />installation, the pore pressures recorded at VWP-B Shallow have fluctuated with periods of <br />slight increase and slight decrease. In general, HBET does not believe that the pore pressure <br />changes in VWP-B Shallow are an indication of instability in CWDA No. 3. <br /> <br />VWP -D <br />VWP-D was installed on October 7, 2014 in the east-central portion of CWDA No. 3. VWP-D <br />was installed approximately ten feet above the base of the gob. Since installation, the pore <br />pressures recorded at VWP-D have fluctuated. The pore pressures increase slightly during the <br />3rd Quarter of 2017. However, this likely reflects the activity at CWDA No. 3 during the <br />monitoring period and the pore pressures decreased between September and December 2017. In <br />general, HBET does not believe that the pore pressure changes in VWP-D are an indication of <br />instability in CWDA No. 3. <br /> <br />General <br />Based upon the results of the most recent VWP monitoring data, HBET does not believe that <br />there is any reduction in the stability of CWDA No. 3. Due to the limited activity at the mine, <br />HBET recommends that the monitoring frequency be reduced to semi-annually. <br />