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Overburden, Interburden, and Underburden Characteristics <br /> Survey information, including date drilled, elevation, location, and coordinates, for the <br /> three Phase I and three Phase II drill hole locations is included with the lithologic <br /> descriptions in Appendix 6-1 . The locations of these holes are shown in Exhibit 6-7. The <br /> analytical results for the six locations are presented in Appendix 6-4. Based upon these <br /> descriptions and the chemical and physical analyses, the following overburden, <br /> interburden, and underburden lithologic units were developed: <br /> Unit 1: All overburden material from the topsoil recovery depth to about 4.0 t 2.0 and <br /> 16.0 t 2.5 feet (mean and standard deviation values) above the top of the upper <br /> and lower Dakota coal seams, respectively. The mean thickness of Unit 1 across <br /> the Nucla East study area is 55.9 feet. The material consists predominantly of <br /> brown to light brownish gray sandstone and light brownish gray to gray sandy <br /> shale. <br /> Unit 2: The upper Dakota coal seam (includes areas where coal is oxidized and weathered) <br /> and encapsulating predominantly dark gray to black carbonaceous shale. The <br /> thickness of this unit ranges from 3.1 to 12.3 feet with a mean and standard <br /> deviation of 6.5 t 3.5 feet, respectively. The mean thickness of the upper <br /> Dakota coal seam within the Nucla East study area is about 1.1 feet. <br /> Unit 3: The middle three to ten feet (mean and standard deviation equal 7.1 t 2.3 feet, <br /> respectively) of interburden consisting predominantly of hard to extremely hard <br /> light gray sandstone and gray shaley sandstone. <br /> Unit 4: The lower two to four feet (mean and standard deviation equal 2.7 t 0.6 feet, <br /> respectively) of interburden directly above the lower Dakota coal seam. This <br /> unit consists of gray to dark gray shale and very dark gray to black <br /> carbonaceous shale. <br /> Unit 5: The lower Dakota coal seam. The lower Dakota coal seam generally ranges from <br /> 4.0 to 7.0 feet (partings omitted) in thickness with an average of about 5.8 <br /> feet. <br /> 6-1-23 Revised 04/11/88 <br />