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Quality Control and Duplicate Samples <br />• Quality control is an important part of the New Horizon 2 overburden, interburden, and <br />underburden monitoring program. One aspect of this quality control program is to have an <br />alternate laboratory <br />facility complete duplicate analyses on five percent of the total samples. On May 22, 1987 <br />Peabody requested that four Phase I samples be shipped from InterMountain Laboratory (IML) <br />in Sheridan, Wyoming to Peabody Central Laboratory (PCL) in Freeburg, Illinois. On November <br />3, 1987 Peabody requested that four Phase II samples be shipped from IML in Farmington, <br />New Mexico to PCL in Freeburg, Illinois. When combined, these 8 samples represent 8 percent <br />of the total samples analyzed (100 samples) for this study. A second part of the quality control <br />program involved having IML complete duplicate analyses on five percent of the total samples. <br />IML completed duplicate analyses on six Phase I samples. The duplicate analyses are given in <br />Attachment 2.04.6-2 (previously Peabody Appendix 6-4). Overall, duplicate analyses were <br />quite similar to the original data. Variation between the original and duplicate analyses data <br />was not significant enough to change the suitability classification of any sample. <br />• The PCL duplicate data was similar to the original IML analyses for pH, EC, SP, Ca, Mg, Na, <br />SAR, AP, NP, ABP, SO4, HC03, N03, SO4, Mo, Mn, Fe, Cd, As, and Ni. PCL duplicate <br />analyses for Pb, Cu, Se, and B were 100 to 500 percent higher than corresponding IML values, <br />but the variation resulted in no change to the suitability classification. PCL duplicate NH4 <br />values averaged about 50 percent less than the IML data. PCL recorded finer particle size <br />analyses than IML. In summary, duplicate data variability was not significant enough to change <br />the suitability classification of any samples. The variability between labs may be attributed to <br />normal laboratory error and slightly different analytical methods. <br />Conclusions <br />Overburden characteristics within the New Horizon 2 study area reflect the variable depositional <br />environments of the coal-bearing strata of the Dakota Formation. Although lateral and vertical <br />variability exist, certain distinct physiochemical differences are apparent between and within <br />some of the Phase I and Phase II sample sites, especially for the parameters pH and acid-base <br />• potential; sand, silt, and clay contents, cation and anion dominance; sulfur type, and sodium <br />REVISED August 2006 2.04.6-43 <br />