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Susan Burgmaier -4- March 20,_2014 <br />assumption may not be valid. At minimum, the presence of phreatic surface <br />needs to be incorporated into all future analyses, <br />BOW2: Please see HBET's response in attached document, section 3.3. <br />13. Also related to pore pressures: is there a potential for Undrained conditions <br />to prevail? This option was considered in studies performed in 2006 and 2007, but <br />deemed inappropriate in later studies. <br />BOW2: Please see HBET's response in attached document, section 3.2. <br />14. Currently there are two functioning VWPs in the upper region of Gob Pile #2 and <br />three at the toe. Is the current number of VWPs sufficient, given the slow rate <br />of dissipation observed in the active areas of the waste pile? Are the VWPs <br />installed there sufficient to provide reliable information about the behavior of <br />coal mine waste disposed of in Gob Pile #3?1 or should additional VWPs be <br />installed at #3? <br />BOW2: Yes, there could be 4 -6 more VWP's north of VWP -06. Also, a plan will be <br />formulated for installation of more VWP's in the mid -slope area, between the <br />existing toe piezometers and the upper piezometers. It is unknown at this time <br />exactly how many more piezometers will be required, but HBET believes getting <br />more installed sooner rather than later is a prudent step to ensure long -term pile <br />stability. <br />Yes, VWP's will be installed at gob pile #3, but HBET has not had a chance to <br />evaluate the stability of that pile. Recommendations for gob pile #3 will be made at <br />a later date and as part of the TR -84 review process. <br />15. Are the consistently high pore pressures measured at VWP -06 and VWP -08 a <br />cause for concern? If not, what level of pressure would indicate that the <br />stability of the pile may be in jeopardy? <br />BOW2: Please see HBET's response in attached document, sections 3.2 & 3.5. <br />16. Coal Mine Waste is achieving the required minimum level of compaction, but the <br />moisture content of the material is well above optimum, and above the level that has <br />been recommended by the geotechnical consultant. This elevated moisture <br />content, combined with the required level of compaction, may be contributing to the <br />extended amount of time required for the dissipation of excess pore pressure. <br />17. In order to counteract the excess moisture that is present in the waste that is <br />generated from the coal preparation plant, dry, native soil /colluvium ( "coverfill ") is <br />routinely blended with the coal mine waste. This mixture is evaluated for density <br />