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• 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 NH,) 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 New Horizon 2 study area. Bore holes completed in 1986 were drilled exclusively with air. Drilling and Collection. Overburden materials are generally sampled by utilizing one or more of the following three methods; continuous cores, cuttings or chips, and highwall or outcrop grab samples. Barrett et al. (1980), Dollhopf et al. (1981), MDSL (1983), Harrington (1983), WDEQ (1985), and USDI-OSMRE (1985b) all recommend that a combination of continuous core and drill cuttings locations be utilized for baseline OlU studies. Continuous coring is primarily utilized during the first phase of an OIU sampling program to document structure and stratigraphy. Subsequently during Phase II, rotary drilled chip samples are preferred to confirm chemical and physical trends because • Revised 9/99 2.oa.6-1o