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• Overburden, Interburden, and Underburden Characteristics <br />Survey information, including date drilled, elevation, location, and coordinates, for the three Phase I <br />and three Phase I I drill hole locations is included with the lithologic descriptions in Peabody Appendix <br />6-1. The locations of these holes are shown on Map 2,04.6-1. The analytical results for the six <br />locations are presented in Peabody Appendix 6-4. Based upon these descriptions and the chemical <br />and physical analyses, the following overburden, interburden, and underburden lithologic units were <br />developed: <br />Unit 1: All overburden material from the topsoil recovery depth to about 4.0 + 2.0 and 16.0 + 2.5 feet <br />(mean and standard deviation values) above the top of the upper and lower Dakota coal <br />seams, respectively. The mean thickness of Unit 1 across the Nucla East study area is 55.9 <br />feet. The material consists predominantly of brown to light brownish gray sandstone and light <br />brownish gray to gray sandy shale. <br />Unit 2: The upper Dakota coal seam (includes areas where coal is oxidized and weathered) and <br />encapsulating predominantly dark gray to black carbonaceous shale. The thickness ofthis unit <br />ranges from 3.1 to 12.3 feet with a mean and standard deviation of 6.5 + 3.5 feet, respectively. <br />• The mean thickness of the upper Dakota coal seam within the Nucla East study area is about <br />1.1 feet. <br />Unit 3: The middle three to ten feet (mean and standard deviation equal 7.1 + 2.3 feet, respectively) <br />of interburden consisting predominantly of hard to extremely hard light gray sandstone and <br />gray shaley sandstone. <br />Unit 4: The lower two to four feet (mean and standard deviation equal 2.7 + 0.6 feet, respectively) of <br />interburden directly above the lower Dakota coal seam. This unit consists of gray to dark gray <br />shale and very dark gray to black carbonaceous shale. <br />Unit 5: The lower Dakota coal seam. The lower Dakota coal seam generally ranges from 4.0 to 7.0 <br />feet (partings omitted) in thickness with an average of about 5.8 feet. <br />Unit 6: The upper ten feet of underburden lying directly below the lower Dakota coal seam. The unit <br />consists of very hard to extremely hard, indurated light gray to light brownish gray sandstone. <br />• Revised 27 Aug 2002 23 <br />