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2. a. Due to a typographic error, the dry density for Test #603 was incorrectly listed as 98.7 <br />pcf on the report. The actual calculated dry density is 88.7 pcf which results in the <br />correct compaction of 91.7% as reported. Please correct the dry density to 88.7 pcf for <br />your records. <br />b. Due to a transcription error from the calculation worksheet to the Daily Compaction <br />Report, Test #647 incorrectly listed the maximum dry density as 107.1 pcf. The correct <br />value is 101.1 pcf which results in a compaction of 88.0% as reported. This test was <br />re- tested as #647A and passed on 6/18/12, as reported. Please correct your copy to <br />reflect an MDD of 101.1 pcf for sample # 647.. <br />c. The maximum dry density for sample #664A is 97.2 pcf but was inadvertently typed as <br />91.2 pcf on the report form. The correct compaction percentage is 95.5% as shown. <br />Please correct the daily compaction report maximum dry density for sample #664A to <br />97.2 pcf in your records. <br />3. Test #561 was re- tested and passed as Test #561A on 4/9/12 as reported on the Daily <br />Observation report for that date and on the Daily Compaction Report (DCR) for 4/9/12. The <br />percentage compaction was inadvertently mis -typed as 90.5% and should be 91.8 %. Please <br />correct the DCR percent compaction to 91.8% for your records. The dry density was 90.5 <br />pcf, not the compaction percentage. <br />4. Because each sample of gob is unique and has a varying amount of coal and rock, we <br />perform the following test procedure to determine MDD and OMC for each sample: <br />• Estimate percentage of rock greater than 3" in the field sample <br />• Determine in -situ moisture and density using nuclear method <br />• Determine percentage of rock greater than 3/4" in the sample in laboratory sieve analysis <br />• Determine the specific gravity of the coal waste and rock in each sample (ASTM C 127) <br />• Determine the in -situ moisture by laboratory method ASTM D 2216 <br />• Using a Proctor value that is appropriate for the range of laboratory values and a CDOT <br />nomograph for rock correction, the appropriate values for MDD and OMC are determined <br />and reported on the DCR form used by Buckhorn to report compaction results. <br />Thanks you very much for your comments on the 2nd Quarter 2012 Instrumentation and <br />Inspection reports. Should you have any questions regarding this letter, please contact me at <br />(970) 497 -8852 or dan(@buckhorngeo.com. <br />Respectfully submitted, <br />Daniel C. Quigley, PE, PG <br />Buckhorn Geotech <br />Cc: File <br />