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West Elk Mine • 2.04.6 Geology Description Introduction The following geologic description of the West Elk Mine permit area is based on publications by C.R. Dunrud (1976), W.R. Junge (1978), Ellis, Gaskill, and Dunrud (1987) and C. Richazd Dunrud (1989); unpublished reports by V. H. Johnson (1948), Geo-Hydro Consulting (1980), Dames & Moore (1983) and Intraseazch, Inc. (1993); considerable subsurface and surface investigations by ARCO (now Mountain Coal Company [MCC]) staff geologists, aerial photo and low altitude aerial and field reconnaissance studies by C.R. Dunrud and J.W. Rold (1994 to 1996), and results from more than 238 drill holes on or near the property. The location of these drill holes is shown on Map 8. Holes are designated "SOM" for those drilled over Federal coal and "MG" for those drilled over private coal. Four holes were drilled on the lease area by the U.S. Bureau of Mines (USBM) in the 1940's which were given a G designation. Twenty-five (2~) holes were completed in 1963 by the U.S. Steel Corporation and designated with the "CSM" prefix. Five additional holes were drilled by Grand Mesa Properties in 1981 and designated "MG-***-81." Grand Mesa Properties completed another hole (CP-82-1) in 1982. In 1992 and 1993, Mountain Coal Company completed 13 drill holes through the B-Seam and were given the designation "JMB." Three holes were drilled to the southwest of the mine site in 1994 and were designated "So. W." (These holes should not be • confused with the shallow wells completed for the subsidence monitoring program and designated as "SW-1"through "SW-6"). Holes drilled from 1993 to 1995, to the east of the mine site, towazd or on Raven Mesa have been designated "RAV". In 1996, 17 holes were drilled and completed through the B-Seam. They aze designated as 96-*-*. The first entry indicates the year that the hole was drilled. The second entry indicates the section in which the hole was drilled, and the third entry indicates the numbered hole in that section. Subsurface control; coal distribution, coal thickness, and quality; overburden and interburden thickness and chemical chazacteristics; structural geology and stratigraphy have been derived by using all of the drill holes. More than 64 holes have been drilled on or within a quarter mile of the Apache Rocks and Box Canyon permit revision areas. The location of those drill holes are included on Map 8. All holes were drilled with permission of landowners and permits from appropriate state and federal regulators. Monitoring wel Is shown on Map 34 and other holes shown on Map 8 were completed or abandoned and reclaimed in accordance with all applicable regulations of the Colorado Division of Minerals and Geology (CDMG) and the State Engineer's Office (SEO) in place at the time. Well completion data and test results have been submitted to the CDMG with Annual Hydrology Reports. Completion data are also provided in Exhibit 12. Normal practice from 1973 through 1991 entailed rotary drilling to approximately 250 feet above the E-Seam where casing was set and coring continued downward through the B-Seam. Since 1992, procedures typically only included spot coring of the E and B-Seams and immediately adjacent strata. The typical suite of geophysical logs run on each hole consisted of various • combination of gamma ray, neutron, density, resistivity, self-potential, temperature logs, and caliper. 2.04-1 5 Revised Jun. 1993 PR06: Revised Jan. 1998 PR08