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Susan Burgmaier 16 -Jul -2014 <br />C-1996-083 2014-Q2 CMW Review Page 2 of 2 <br />For the 2nd Qtr 2014, compaction testing was performed by HBET. The MDD values to which the field <br />densities (DD) are compared are not unique to each field test. Rather, it appears that HBET may have <br />established (at least) three separate "Proctor" Curves in the laboratory, to which the Gob at a particular <br />spot can be compared. This technique, though different from that employed by Buckhorn, is commonly <br />used in highway construction projects. Samples of soil are collected which span the full range of <br />materials that are likely to be encountered during the project (clayey, silty, sandy, rocky, or <br />combinations of these). A suite of Curves is created, and the field technician then chooses the <br />appropriate Curve to be used for comparison for the material that is being compacted at a given time. <br />(There is definitely a knack to choosing the right Curve.) <br />The three HBET MDD reference values are also plotted in the graph above. As we can see, the first two <br />MDDs (at 104.0 and 106.0 pcf) are somewhat higher than the average observed to date, but they are <br />well within in the range that we might expect to see. The third MDD, however, at 79.5 pcf, is lower than <br />even the Minimum result obtained by Buckhorn over the course of 2 -plus years. In the 2nd Qtr report, <br />this third curve was referenced on four separate tests, three of which "passed" with densities >100%. <br />1) 1 would like to request that BRL provide a description of the process now being used to <br />evaluate compaction of the Coal Mine Waste at the Bowie No. 2 Mine. They should include <br />copies of any Proctor curves that have been generated for Gob at the site, together with any <br />differentiating factors for each Curve that the tester will be using so the proper Curve is <br />selected for reference with each test. <br />2) Depending upon the rationale provided for using an extremely low MDD (79.5 pcf) as a <br />reference, it may be appropriate to utilize a different Proctor Curve for those four test <br />locations. <br />With respect to the 2nd Qtr 2014 Instrumentation Report, I have two comments: <br />1) The pore pressure at VWP-06 has begun to rise sharply (as shown on Buckhorn's July 1, 2014 <br />Figure 2) since the previous reading in May 2014. What pressure for this installation would <br />be a cause for concern for the stability of CWDA#2? <br />2) Given the sharp rise in pore pressure observed at VWP-06 in June, I recommend that the <br />monthly VWP monitoring frequency be continued, at least for VWP-06 and possibly VWP- <br />08. 1 do not believe it is necessary to monitor VWP-05, -09 and -10 more frequently than <br />once per quarter. <br />This concludes my review of the 2nd Quarter 2014 Coal Mine Waste Bank and Instrumentation <br />Monitoring Reports. Please let me know if you have any additional questions. <br />cc: David Berry, DRMS <br />