2008-11-10_PERMIT FILE - C1996083

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r~ LJ VWP-04 tlamaged ~ 12.0 :~ between Sr 16106 _ _ _ . and 10/20/06 r r ~.~_ _ 10.0 "~r VWP-0t damaged ~` ~~ _ . i fj' between 10!20!06 ~s•~~ `j'J~ and 1l311U7 .-. .N a 8,0 f ~ ~ /i ~ m ~-.vwP of N h 0 - __ _« VWP-02 - __ m tl +VWP-03 m ~i ~-- VWP 04 ~ a - - a__ ------ra-__ ---- ---a ~r--.-.a U0 . ~ '~rtin'; ~".-+'u, 1 .1~'i;~-~i, ~.~.iii~, 1:-.7:'r'(>6 4!21?07 A(19~07 12117!07 4i 15,+08 A113+08 Date Figure 1. Summary of Pore Pressure Monitoring Pore pressures measured at VWP-O1 and VWP-04 peaked at 8.2 and 9.3 psi, respectively. These peak values correspond to approximately 19 and 21.5 feet of head. The pore pressures were observed to begin to decrease approximately one year after installation. As previously indicated, piezometers VWP-01 and VWP-04 were damaged shortly after the observed pore pressure decrease and further monitoring was not possible. Monitoring of VWP-03 shows a peak pore pressure of 12.2 psi approximately 1.5 years after installation. This is the maximum measured pore pressure in any of the piezometers to date. It is not a surprise that the maximum pore pressure has been measured in VWP-03, as this piezometer has the longest drainage path of any of the piezometers as it is located in the central interior of the waste bank. Still, pore pressures have been measured to dissipate steadily after achieving a peak value. This demonstrates that pore water drainage is taking place in the coal mine waste. Consequently, a total stress ~=0 stability evaluation is not appropriate. As further discussed in Section 5, an effective stress analysis using the measured pore pressures is appropriate for evaluation of the stability of the coal mine waste bank. E10\t1~ Vu _' ?fN1~ Ktrvalutiun of Ccuil R1inr. Wastr Stabiltt~.d~x~ I'agr G of I