2014-11-13_REPORT - C1996083 (2)

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INTEROFFICE MEMORANDUM Date: 13 November 2014 To: Susan Burgmaier, Lead Specialist From: Marcia L. Talvitie, P.E. Subject: Bowie No. 2 Mine (Permit No. C- 1996 -083) Review of 3rd Qtr 2014 Coal Mine Waste Bank and Instrumentation Report At your request, I have reviewed the above - referenced report submitted by J.E. Stover & Associates on October 22, 2014. Approved Placement, Compaction, and Inspection requirements for Coal Mine Waste (Gob) are found in Volume IX, pp. 12 -14 and Volume XI, pp. 8 -9. Compaction Testi During this quarter, coal mine waste placement and compaction activities alternated between Gob Pile #2 and Gob Pile #3. All compaction testing was performed by Huddleston -Berry Engineering & Testing, LLC (HBET), at a frequency of approximately once per week. A total of 100 compaction tests were performed, including one re -test for a site that initially failed to obtain the required 90% of Maximum Dry Density (MDD). Moisture contents of the emplaced coal mine waste were noticeably lower than results reported in previous quarters. This favorable condition was achieved even without BRL's needing to incorporate as much coverfill material as they have in the past. HBET's detailed report of materials testing for the 3rd quarter included a series of Moisture - Density Relationship Curves that were developed in the laboratory and are used to evaluate the relative compaction of coal mine waste. The eight curves are summarized in Attachment 1 to this memo. In Table 1 of Attachment 1, the curves are arranged by "Sample No. ". Gradation, Atterberg Limits, and Description fields are filled in where this information was provided with the curve(s) by HBET. At the far right, columns have been added to show how many times each curve was used as a reference during the 2nd and 3rd quarters of this year. In Table 2, the same curves have been re- arranged in order of decreasing "MDD ". As shown in Table 1, the curve being used with the greatest frequency is Sample No. 14 -0195. Aside from the source being identified as "Gob #3 Borrow Blend ", no other properties are provided (Gradation, Atterberg Limits, or Classification). The Division has reviewed the 2nd and 3rd quarter compaction results where this curve was used. That data is compiled in Attachment 2, which shows the Compaction achieved, among other results. As highlighted in yellow, the compaction fell slightly below 90.0% with some regularity (although all tests would be at least 90 if rounding is employed).