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Susan Burgmaier <br />C- 1996 -083 TR -84 PAR #3 <br />02 -Jul -2014 <br />Page 4 of 6 <br />a) Please expand the TR -84 (and any current or future) stability analysis to include <br />the results of any additional laboratory testing that has been conducted on coal <br />mine waste at the Bowie No. 2 Mine. <br />MLT 07102: Laboratory data for Consolidated - Undrained triaxial shear testing is <br />presented in Appendix A of the HBET analysis. As explained in HBET Section 3.0, <br />samples of blended material from Gob Pile #3 were collected and tested. HBET <br />does not describe what this "blended material" is, and it does not appear that the <br />Volume XI text describes the practice of blending wet coal mine waste with <br />available coverfill to achieve a desirable moisture content for placement. Please <br />revise the Placement and Compaction section in Volume Xl to address the <br />blending process. <br />b) For the native soil, an assumed 4 of 34 degrees was used. This value is not <br />consistent with the 4 of 30 degrees that was determined by Buckhorn in Mar - <br />2007, based on laboratory testing of on -site materials. Please provide <br />justification for using a revised value for the angle of internal friction of native <br />soil, or revert to using the original value. <br />MLT 07/02: HBET's 11- Jun -2014 analysis utilized a cp of 30 degrees for the native <br />soil. This item is resolved. <br />9 (45) MLT 03/06: The third bullet in the Assumptions section of the 15- Oct -2013 Buckhorn <br />analysis refers to piezometers at Pile #3 that were monitored in June 2013 (no <br />groundwater was observed). The Mar -2007 Buckhorn report approved under TR -45 <br />documents the installation of seven standpipe piezometers in the footprint of <br />CMWDA #3. Based on readings taken in Nov -2007, a phreatic surface was developed for <br />use in the various stability analyses. <br />a) Please expand the discussion of the groundwater phreatic surface to address the <br />condition of each of the piezometers installed in 2007. Which of these <br />piezometers have been disturbed or destroyed? Which, if any, are still in use? <br />What piezometers were utilized in 2013? <br />MLT 07102: Subsection 4.3 of the HBET analysis discusses the location of the <br />natural piezometric surface based on elevations observed in the piezometers <br />installed in 2006. HBET does not state which of the piezometers were monitored <br />by Buckhorn in June 2013. Please clarify the status (functioning or destroyed) of <br />each of the original seven standpipe piezometers. This clarification could be <br />accomplished in either the Volume XI text or in the HBET analysis. <br />b) The current analysis fails to consider the effects (if any) of the sub - excavation of <br />soil from the footprint of the pile on the proximity of the phreatic surface. <br />Please expand the analysis to consider Buckhorn's original predicted location of <br />the groundwater phreatic surface (based on the seven standpipe piezometers) <br />and the approved additional excavation of soil material from the footprint of the <br />pile. <br />