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is most conononly associated with the top soil layer and the sandstone units. The highest <br />• pH, 8.9 occurs in #882E in the lowest part of the sandstone directly over the upper Dakota <br />coal's thin encapsulating shale. <br />Acid-base potential (ABP) ranges from -48 to 239. The more acidic ( 0 ABP) material <br />occurs most commonly above the upper Dakota coal. The more basic (+0 ABP) material most <br />commonly occurs in the upper 10 ft of overburden material or in the soil layer. Core <br />#871E contains both of the extreme ABP numbers where the +239 ABP is found in tfie upper 3 <br />ft of soil, and the -48 ABP if found directly above the 0.5 ft thick shale layer <br />encapsulating the upper Dakota coal. Pyrite occurs within the coals, in the few feet of <br />material surrounding the coals, and occasionally in isolated pockets higher in the <br />overburden sequence. The percent pyritic sulfur calculated for the overburden ranges from <br />.03 to 1.6. <br />Interbu rden Material. The interbu rden is defined as all material above the lower <br />Dakota coal seam up to and including the upper Dakota coal seam. It is divided into three <br />separate units, Units 2, 3, and 4; Unit 2 consists of the upper Dakota coal and <br />• encapsulating shale or sandstone layers. Unit 4 consists of only the shale layer directly <br />above the lower Dakota coal, and Unit 3 comprises the remaining material which is most <br />commonly a thick sandstone. <br />The thickness of the interburden remains fairly constant throughout the study area varying <br />from 17 ft in the southwestern part to about 14 ft in the central and eastern part. The <br />thickness of upper Dakota coal varies from 7.3 ft in the west to less than 0.5 ft in the <br />east (Table 17-7). <br />Core #870E contains naturally-occurring low concentrations of Cu, Pb, Zn, Ni, Mg, B, Se, <br />Mo, Fe and Mn. Analyses of soil pH show a range in Unit 2 from 3.5 to 8.9, in Unit 3 from <br />6.0 to 9.0, and in Unit 4 from 4.2 to 7.9. The most acidic material occurs in #871E (3.5) <br />within the shales surrounding the upper Dakota coal. The shale above the coal has a pH of <br />3.6 and below the coal a pH of 3.5, with a total thickness including the coal of about <br />7.1 ft. For the entire Nucla East area this is the most acidic material that is found. <br />The most basic material occurs in #882E Unit 3 with a pH of 9.0 and thickness of 2.9 ft <br />• and in Unit 2 with a pH of 8.9 and thickness of 2.8 ft. Again, these anomalously high pH <br />values are found in the encapsulating shales or sandstones of the upper Dakota coal. <br />17-35 Revised 04/11/88 <br />