2008-10-03_REPORT - C1981010 (3)

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Page 1 of 2 Jim Mattern From: Samrat Mohanty [smohanty@agapito.com] Sent: Monday, September 08, 2008 2:22 PM To: Jim Mattem Cc: greg@trappermine.com; DeeDee Ross Subject: Slide monitoring frequency (534-21-7) Dear Jim, Please find below my observations from the data provided by Greg and Graham, and recommended frequency of monitoring. Observations: 1. Four monitoring stations upslope (south/southwest) of the slide area (red circles) have been displaced more than a few feet. 2. Positive correlation was observed between movement of monitoring stations on the landslide block and preceding rainfall/snowfall events. I believe that there cumulative through-seepage of snow-melt and rainfall are major factors behind the post-slide movements. 3. Majority of incremental movements (both horizontal and vertical) within the slide area were found to be less than 3 in. 4. Survey data from several monitoring stations within the landslide block (green circles) indicate that these specific areas have stabilized. 5. Data from many of the monitoring stations within the slide block (yellow circles) present ambiguity as to whether these monitoring stations have come to complete rest. Only further collection of data may be able to clarify their trend. 6. Piezometer data at 07-GX5-CCR (L-M interburden mudstone at 149 ft depth) exhibited elevated piezometric head (currently at 22.7 psi) over nine months. This may be cause of concern as this borehole is located within the block that is to be mined through K-A cuts. Piezometric head at 07-G13-CCR has stayed consistently within the range 33-35 psi (along Q-Seam mudstone within the slide block), indicating an elevated pore pressure and potential for possible slippage. Piezometric data for 07-G110- CCR exhibited increases in head at 176-ft (mudstone) and 200-ft (bottom of coal). 7. Data from the only inclinometer (at 07-G12-CCR) indicates there has been a very slight movement of less than 1 inch movement, possibly along the K-roof mudstone. Based on the displacement data, local rainfall/snowfall records and piezometer data provided by TMI, it is difficult to conclude that the entire slide block has come to a rest. I believe that southern (upper) half is relatively more stabilized as compared to the northern (lower) half. However, given the, elevated piezometric heads observed at all the piezometer locations, large future movements cannot be totally ruled out. The monitoring frequency that was recommended earlier may be slightly modified taking in to account the relatively small incremental-displacements within the landslide block, as follows: Survey of Surface Benchmarks and Inclinometer: • Once per month during dry season • Once per week for two weeks following a major rainstorm event (>0.5 inch) or major snow melt (loss of cover >2 inches) Piezometers: • Once per month during dry season 09/30/2008