2016-04-15_HYDROLOGY - C1996083 (7)

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CWDA No. 3 #01349-0001Huddleston-Bevy 04/13/16 aEF�rF�fn�,.�« 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. The pore pressures recorded at VWP-A Deep generally decreased since installation until September 2015. Between September and December 2015, the pore pressures increased slightly. However, the pore pressures dropped significantly since December 2015. This is consistent with the fact that no coal mine waste was placed near the instrument during the winter months. 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. V" -A Shallow VWP-A Shallow was installed on October 6, 2014 near the northern edge of CWDA No. 3. VW -A Shallow was installed approximately ten feet above the base of the gob. After installation, the pore pressures dropped until November 2014. Between November 2014 and September 2015, increases in the pore pressures were recorded at VWP-A Shallow. However, between September 2015 and March 2016, the pore pressures decreased. The increases through September 2015 likely reflect the active gob placement at CWDA No. 3 which slowed down and then stopped during the winter months. In general, 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. V" -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. Between March and September 2015, the pore pressures at VWP-B Shallow increased. However, between September 2015 and March 2016, the pore pressures decreased. The increases through September 2015 likely reflect the active gob placement at CWDA No. 3 which slowed down and then stopped during the winter months. In general, HBET does not believe that the pore pressure changes in VWP-B Shallow are an indication of instability in CWDA No. 3. VWP-1) VW -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 between June and September 2015. Between September 2015 and March 2016, the pore pressures again decreased. This likely reflects active gob placement at CWDA No. 3 during the summer and early fall and then cessation of placement during the winter months. In general, HBET does not believe that the pore pressure changes in VWP-D are an indication of instability in CWDA No. 3. X:\2008 ALL PROJECTS\01349 -Bowie Resources, LLC\01349-0001 Bowie Mine\200 - Geo\Gob Anstrumentation Monitoring\2016\01349-0001 GP3 1stQ 2016 LR041316.doc 2