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USDI-OSMRE (1985e) recommends drilling 1 hole/160 acres with a minimum of 3 holes/site. • <br />YDEp (1985) etlpulates sampling 2 tore holes and 6 cuttings holes per 640 acres during <br />Phase I drilling. Phase lI sampling is reserved for special handling situations and e <br />density of 1 hole/40 acres is recommended. Dollhopf et el. (1981) recommends a 600-meter <br />grid (1 hole/90 acres) for initial characterization followed by additional drilling end <br />analyses ff any parameters of concern are indicated in the initial drilling. The circular <br />zone of date extrapolation or the effective drill hole radius should be 750 feet. lastly, <br />Sutton et al. (1981) recommends sampling 1 site to adequately assess overburden <br />variability on small permit areas of less than 40 acres. <br />A Phase I drilling program was implemented at Yoast in 1980 Sn conjunction with a USGS <br />ground water study to describe overburden characteristics over the entire study area, to <br />obtain representative core hole locations from which cross sections could be developed, <br />and to define the extent of suitable, marginally suitable, and unsuitable materiel. <br />Ten strategic and systematic drilling locations, spaced 1000 to 3000 feet apart, were <br />selected after evaluating the geologic cross section requirements and existing coal <br />eropline/recovery information. Wedge overburden (defined as all stratigraphy above the <br />Wedge cost seam) thickness at Sites 2311E, 2314E, 2318E, 2309E, 2316E, 2315E, 2317E, end • <br />2310E was about 13, 33, 33, 70, 92, 95, 104, and 139 feet, respectively (Exhibits 6-3 and <br />6-4). Wolf Creek overburden (defined as ell stratigraphy below the bottom of the Yedge <br />seem end above the Yolf Creek seem) thickness at Site 2313E was approximately 61 feet. <br />Neither coal seam occurred at Site 2312E. The locations of these hales art shown on <br />Exhibit 6-4. The Phase I sampling density of 1 hole/50 acres meets the hole intensity <br />criteria discussed above to adequately describe the overburden variability. Drill hole <br />descriptions end chemical/physical analysis indicated there is little horizontal <br />variability in the local depositional environment. <br />Sample Contemirietion. Numerous overburden sample contamination problems have been <br />documented over the last 15 years in the western United States. Drilling fluids, foam <br />additives, end muds can appreciably effect the soluble constituents (especially EC, SAR, <br />end NH4) in the sample. During rotary drilling for cores or Cuttings, it is necessary to <br />use a drilling medium such es air, water, or mud for Lifting cuttings from the borehole. <br />For overburden baseline studies, it is recommended air be used whenever possible, water <br />second, end mud (or foam) avoided unless absolutely necessary to overcome circulation <br />problems or to lift cuttings from deep holes (Barrett et al., 1980; Power and Sandoval, ~ • <br />1976; Dollhopf et al., 1981; and Peabody Coal Company, 1987). A chemical analysis should <br />be obtained on the water, foam, end/or dr(ll(ng mud whenever they ere utilized. <br />12 <br />