1988-04-11_PERMIT FILE - C1981008A (5)

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A Phase I drilling program was implemented at Nucla East in 1984 to describe overburden, interburden, .and underburden characteristics over the entire study area, to obtain representative core hole locations from which cross sections could be developed, and to define the extent of suitable, marginally suitable, and unsuitable material . Three strategic and systematic drilling locations, spaced at 2,000 and 3,000 feet apart, were selected after evaluating the geologic cross section requirements and existing coal cropline/recovery information. Overburden (defined as all stratigraphy above the upper Dakota coal seam) thickness at Sites 871E, 870E, and 872 was approximately 30, 60, and 100 feet, respectively. The locations of these holes are shown in Exhibit 6-7. The Phase I sampling density of 1 hole/160 acres meets the hole intensity criteria discussed above to adequately describe the OIU variability. Contamination. Numerous overburden sample contamination problems have been documented over the last 10 years in the western United States. Drilling fluids, foam additives, and muds can appreciably affect the soluble constituents (especially EC, SAR, and NH4) in the sample. During rotary drilling for cores or cuttings, it is necessary to use a drilling medium such as air, water, or mud for lifting cuttings from the borehole. For overburden baseline studies, it is recommended that air be used whenever possible, water second, and mud (or foam) avoided unless absolutely necessary to overcome circulation problems or to lift cuttings from deep holes (Barrett et al., 1980; Power and Sandoval, 1976; Dollhopf et al ., 1981; and Peabody Coal Company, 1987). A chemical analysis should be obtained on the water, foam, and/or drilling mud whenever they are utilized. Random sample contamination often results in serious misinterpretations of the data. Many previously reported unsuitable copper, molybdenum, zinc, and especially lead concentrations were more apt to have been caused by drill stem grease contamination than natural mineralized strata. Dollhopf and Goering (1983). Dollhopf et al . (1981), Peabody Coal Company (1986), and Rochelle Coal Company (1984) all demonstrated that significant contamination resulted from zinc, copper, molybdenum, and lead based drill stem joint lubricants. A noncontaminating drill stem joint lubricant should be utilized when copper, lead, zinc, or molybdenum are included on the baseline parameter list. A noncontaminating drill stem joint lubricant (lithium based) was utilized at all 1986 sample sites within the Nucla East study area. Bore holes completed in 1986 were drilled exclusively with air. 6=1-13 Revised 04/11/88