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or exceeded guideline levels during the Phase I sampling were included on the Phase <br />II analyses list. Modifying the second phase parameter list was desirable to reduce <br />unwarrantable analyses costs and to focus on site specific conditions. <br />Sampling Methodology -Phase I <br />In e i .Most OIU sampling and analysis studies indicate that drilling designs should be governed <br />by geological factors, such as the lithologic variability and the depositional environment of the OIU <br />strata (Barth et al., 1981). Barrett et al. (1980) states that drilling designs and hole spacings must be <br />determined on the basis of the unique set of geologic and geochemical conditions (i.e., lateral <br />variability of strata) existing at each mine site. <br />Recommended drilling intensities range from 1 hole per 40 acres to 1 hole per 640 acres. DMG <br />(1982) suggests sampling 1 drill hole/640 acres with a minimum of 3 holes/site. USDI-OSMRE <br />(1985a) recommends drilling 1 hole/160 acres with a minimum of 3 holes/site. WDEO (1985) <br />stipulates sampling 2 core holes and 6 cuttings holes per 640 acres during Phase I drilling. Phase <br />II sampling is reserved for special handling situations and a density of 1 hole/40 acres is <br />recommended. Dollhopf et al., (1981) recommends a 600 meter grid (1 hole/90 acres) for initial <br />characterization followed by additional drilling and analyses if any parameters of concern are <br />indicated in the initial drilling. The circular zone of data extrapolation or the effective drill hole radius <br />should be 750 feet. Lastly, Sutton et al. (1981) recommends sampling one site to adequately assess <br />overburden variability on small permit areas of less than 40 acres. <br />A Phase I drilling program was implemented at New Horizon 2 in 1984 to describe overburden, <br />interburden, and underburden characteristics over the entire study area, to obtain representative core <br />hole locations from which cross sections could be developed, and to define the extent of suitable, <br />marginally suitable, and unsuitable material. Three strategic and systematic drilling locations, spaced <br />at 2,000 and 3,000 feet apart, were selected after evaluating the geologic cross section requirements <br />and existing coal cropline/recovery information. Overburden (defined as all stratigraphy above the <br />upper Dakota coal seam) thickness at Sites 871 E, 870E, and 872 was approximately 30, 60, and 100 <br />feet, respectively. The locations of these holes are shown on Map 2.04.6-1. The Phase I sampling <br />• Revised 9/99 2.04.6-9 <br />