1988-04-11_PERMIT FILE - C1981008A (4)

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drilling programs can decrease OIU characterization cost substantially without jeopardizing the quality of data obtained. The following tasks were accomplished during the two phases of OIU analyses: Phase I: The existing OIU data from the seven overburden baseline locations were reviewed and analyzed, potential chemical and physical problems were identified, and general areas of suitable and unsuitable overburden were outlined. Phase 11: Four additional sampling locations were approved for the scraper pit on April 14, 1986 by CMLRD (Peter O'Connor's letter to Vern Pfannenstiel). This program was completed to accurately characterize the extent of suitable and unsuitable material. Constituents which approached or exceeded guideline levels during the Phase I sampling were included on the Phase II analyses list. Modifying the second phase parameter list was desirable to reduce unwarrantable analyses costs and to focus on site specific conditions. H. CROP/SUBCROP DRILLING Twelve exploratory holes will be drilled in order to better define the crop/subcrop boundary. The holes will average 50 feet in depth, and will be 5-1/8" in diameter. See Exhibit "6-12" for the hole locations and access. No topsoil removal or blasting will be required. Access to the holes will be limited to overland travel with no bladework required. The holes and access will be reclaimed unless they fall within the mine plan which may be revised based upon the drilling results. If reclaimed, the drill holes will be sealed by replacing the drill cuttings, and placing a suitable plug 10 feet below the ground surface to support a cement plug within 3 feet of the ground surface. The top 3 feet will be covered with the drill cuttings or dirt. Sampling Intensity. Most OIU sampling and analysis studies indicate that drilling designs should be governed by geological factors, such as the lithologic variability and the depositional environment of the OIU strata (Barth et al., 1981). Barrett et al. (1980) states that drilling designs and hole spacings must be determined on the basis of the unique set of geologic and geochemical conditions (i.e., lateral variability of strata) existing at each mine site. Recommended drilling intensities range from one hole per 40 acres to one hole per 640 acres. CMLRD, 1982 suggests sampling 1 drill hole/640 acres with a minimum of 3 holes/site. USDI-OSM (1985A) recommends drilling 1 hole/160 acres with a minimum of 3 holes/site. WDEQ (1985) stipulates sampling 2 core holes and 6 cuttings holes per 640 acres during Phase I drilling. Phase II sampling is reserved for special handling situations and a density of 1 hole/40 acres is recommended. (Rev. 9/92) 6-19 tit R'IS