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<br />River and to just past the torn of Nucla to the east. This study area was delineated by s <br />maximum area of potential influence. <br />For the Nucla Esst area, greurM water is legated within the overburden, interburden or <br />underburden materi of a. The overburden includes Unit 1 only, er all materi at above Dut not <br />i nel udi nq the upper Dakota coal seam. The lnterhurden ineludas UnTCS 2, 3, and 4 whf ch is <br />a17 material above the lower Dakota coal seam up to and 1nelutling the upper Dakota coal <br />seam. The Dakota coal eonsi ats of Unit 5 only, and the untlerburden, Unit 6, ineludas only <br />the materlal di really below the lower Dakota coal seam. Data usetl for core analyses are <br />from core holes S870E, le877E, OB72E, 1881 E, i882E, arM 1886E. Data used for groundwater <br />analyses era frps Walls 091-N6, -N13, -N14, -N75; -N16i -Nt7; -N18, -N19i 'N20; -N2ti and <br />-N22. Sempl sa from Wells GW-N29, CW-N30, CM-N31, L71-N32, GN-N33 and GW-N34 have not been <br />collected to date. <br />Overburden, Interpurden and Untlarburden Characteri zatfon. <br />Overburden Material. The overburden mated al consists primarily of thick sequences <br />of sandstone lnterbadded M th shale, carbonaceous shale, and silt. The sandstone unite <br />• grade to thickness Fran lean 'than 10 ft in the eastern part of the perm It area to over 3D <br />ft fn the western part. The shales are most prevalent above the upper Dakota coal and <br />range in thickness from lass than l ft to B ft (Table 17-6). <br />Laboratory tests on cores provide information on the chemical properti ea of the materlal. <br />OT pri ne importance W rile water quality era the psraaeters acid base potential (ABP) and <br />paste pH. These ors di scuaaed in the Controls on Ground Water puality Sects on. Brfefly, <br />negative values of ABP indicate the potential for the production of acid by oxi datf on of <br />pyrite, and the paste pH indicates whether reactive pyrite to present. <br />The overburden contains low concenirati ons of naturally-xcurri ng trace elements such as <br />B, Se, No, Fe, Nn, Cu, PD, Zn, N1, Cd and Hq. So11 pH analyses show pests pH's range from <br />3.7 to 8.9 but average abouC 7.2. The most ac tdfo pH mated ai-((4.5) occu ra only in core <br />holes M882E and f886E. Generally, the tow pH (<S.5) nwterf al occurs to the far eastern <br />part of the si ta, does not occur to Na cantrei or western part, end is usually found in <br />the shale di racily above the upper Dakota coal. In Y882£ Che maximum thickness of the 3.7 <br />pH zone 1s about O.5 ft, and in aB86E the 4.3 pH zene is about 4.5 ft thi ek. The baste pH <br />material (>7.7) occurs sporadically ifiroughout the unit in all core hole8 except a886E and <br />77-33 Revi aed 04/11/88 <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(3}2-41 <br />