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• <br />Unit 6: The upper ten feet of underburden lying directly below the lower Dakota coal seam. The <br />unit consists of very hard to extremely hard, indurated light gray to light brownish gray <br />sandstone. <br />L J <br /> <br />These lithologic unit designations are typical for the Dakota Sandstone Formation and are similar <br />to those utilized in Mine Pit Areas 2, 3, and 5 at the New Horizon 1 mine area. The lithologic unit <br />designations for the New Horizon 2 study area are included with the lithologic descriptions in <br />Attachment 2.04.6-1. <br />Overburden, Interburden, and Underburden Suitability <br />The criteria for assessing the suitability of overburden or Interburden for a root growth medium or <br />aquifer restoration material are as presented in Table 2.04.6-3. The suitability limits for each <br />parameter are documented by current literature citings. <br />The following techniques were used to analyze the Phase I and Phase II overburden, Interburden, <br />and underburden sample data. Initially, statistical analyses (mean and standard deviation) were <br />completed to determine the variability between lithologic units and from core to core. Since <br />sampling intervals varied with depth, weighted means were calculated for all physicochemical <br />parameters for each lithologic unit, excluding topsoil. These means will likely be representative of <br />the physicochemical concentrations that will be present in the scraper and dozer handled spoiled <br />overburden and Interburden sections. Second, the unsuitable composition for each lithologic unit <br />was determined and utilized to implement effective and efficient overburden and Interburden <br />handling techniques. Lastly, other mitigative measures are discussed where necessary. <br />Mean physicochemical values for each parameter are listed by drill hole number and lithologic unit <br />in Tables 2.04.6-4 through 2.04.6-8. Approximately 93 percent of all mean values (239) fall within <br />the suitable and marginally suitable ranges as outlined by the assessment criteria listed in Table <br />2.04.6-3. Exceptions include the unsuitable pH values for Unit 2 (Hole 871 E) and Unit 4 (Holes <br />872E and 886E), the unsuitable SAR for Hole 882E (Units 2, 3, and 4); and the unsuitable acid <br />base potential values for holes 870E, 871 E, 881 E, 882E (Units 2 and 4) and for Unit 4 (Holes 872E <br />and 886E). An evaluation of these unsuitable parameters is contained in the Mitigative Measures <br />section. <br />REVISED August 2006 2.04.6-29 <br />