2015-10-19_REPORT - C1996083 (2)

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CWDA No. 3 #01349-0001+ ) Huddleston -Berry 10/14/15 enrmnrmas t = mg, uc Discussion of Vibrating Wire Piezometers VWP-A Deep VWP-A Deep was installed on October 6, 2014 near the northern edge of CWDA No. 3. VWP- A Deep was installed in the foundation soil approximately eight feet below the bottom of the gob. Since installation, the pore pressures recorded at VWP-A Deep have generally decreased. In general, HBET does not believe that the pore pressure changes in VWP-A Deep are cause for concern regarding stability of the gob pile. VWP A Shallow VWP-A Shallow was installed on October 6, 2014 near the northern edge of CWDA No. 3. VWP-A Shallow was installed approximately ten feet above the base of the gob. After installation, the pore pressures dropped until November 2014. However, since that time, slight increases in the pore pressures have been recorded at VWP-A Shallow. In general, the increases in pore pressures at VWP-A Shallow are likely due to gob placement at CWDA No. 3. However, HBET does not believe that the pore pressure changes in VWP-A Shallow are an indication of instability in CWDA No. 3. VWP-B Deep VWP-B Deep was installed on October 6, 2014 in the west -central portion of CWDA No. 3. VWP-B Deep was installed in the foundation soil approximately ten feet below the bottom of the gob. Since installation, the pore pressures recorded at VWP-B Deep have been fairly constant. HBET does not believe that the pore pressure changes in VWP-B Deep are an indication of instability in CWDA No. 3. VWP-B Shallow VWP-B Shallow was installed on October 6, 2014 in the west -central portion of CWDA No. 3. VWP-B Shallow was installed approximately ten feet above the base of the gob. Since installation, the pore pressures recorded at VWP-B Shallow have fluctuated with periods of slight increase and slight decrease. Since March 2015 there has been an increase in the pore pressures at VWP-B Shallow. However, this likely reflects active gob placement at CWDA No. 3. In general, HBET does not believe that the pore pressure changes in VWP-B Shallow are an indication of instability in CWDA No. 3. u►,VMS] VWP-D was installed on October 7, 2014 in the east -central portion of CWDA No. 3. VWP-D was installed approximately ten feet above the base of the gob. Since installation, the pore pressures recorded at VWP-D have fluctuated. However, there was a slight increase in pore pressures since June 2015. However, this likely reflects active gob placement at CWDA No. 3. In general, HBET does not believe that the pore pressure changes in VWP-D are an indication of instability in CWDA No. 3. Site Visit Observations HBET visited the site on October 6, 2015. At the time of our visit, no mine waste was being placed at CWDA No. 3. However, the contractor was moving rip -rap at the toe of the coverfill stockpiles east of CWDA No. 3. X:\2008 ALL PROJECTS\01349 -Bowie Resources, LLC\01349-0001 Bowie Mine\200 - Geo\Gob 3\Imtr ntation Monitoring\01349-0001 GP3 3rdQ 2015 LR101415.doe 2