PERMFILE47424

• Permit No: C1994082
• IBM Index Class Name: Permit File
• Doc Date: 10/6/2004
• Doc Name: Geotechnical Design & Operational Considerations for Highwall Mining, IIW & Yoast Areas
• Section_Exhibit Name: Tab 12 Attachment 12-3 Part 2
• Media Type: D
• Archive: No

• What operational measures can be taken to increase highwall mining efficiency
and safety?
To best address these questions, NSA's evaluation was conducted by completing
three Tasks, including (1) site characterization (review of site conditions and current
highwall stability, core recovered from the Yoast Area, physical.property testing, etc.);
(2) engineering design (empirical and numerical modeling evaluation of optimal mining'
plans for the Seneca IIW and Yoast Areas); and (3) operational considerations
(identification of relative risks to mining by pit, production efficiency, potential for out-
of-seam product dilution etc.).
By combining NSA's practical experience with the latest empirical and numerical
modeling techniques, this evaluation provides Peabody Energy with productive and safe
procedures for highwall mining at the Seneca Mine.
2.0 SITE CHARACTERIZATION
The site characterization effort consisted of a site visit, review of available data,
and physical property testing of previously recovered core.
• 2.1 Site Geology and Seam Settings
The target Wolf Creek, Sage Creek, and Wedge Seams at the Seneca Mine occur
in late cretaceous sediments of the Williams Fork Formation of the Mesa Verde Group
(Highwall Mining Services, HMS, I998). The sediments consist primarily of sandstone
interbedded with shales, siltstones, and coal. The Seneca IIW Area is on the western
limit of the Sage Creek Anticline, resulting in steep west-northwest dips typically in the
10° to 20° range. In the Yoast Area, the Fish Creek Anticline is responsible for wesi-
northwest dips between 10° to 17°.
Peabody provided seam model information to NSA, including isopachs of coal
thickness, overburden, interburden, and bottom structure. It should be noted that the
Wolf Creek Seam in southern portions of Seneca IIW have not been drilled in some azeas
where highwall mining is planned; therefore, there may be inaccuracies in the seam
model there. Seam model data for Seneca IPvV are shown in Figures 2 through 12; the
same data for Yoast are shown in Figures 13 through 19. Representative cross sections
from the two areas are shown in Figures 20 and 21. A summary of the characteristics of
the two areas is presented in Table 1.
NOTE: In Figure 20, sections B-B' and C-C', the Wolf Creek Seam was positioned 60 ft
lower than the seam bottom contours shown in Figure I I. This was done to separate the
• Wolf Creek from the overlying seams, Seneca Mine management indicated that drilling
data are lacking in this area, and that the Wolf Creek contours provided are likely
inaccurate. Sections B-B' and C-C' were specifically taken to investigate the potential
for Wolf Creek mining to interact with the previously mined Wedge Seam. Due to the

Seneca Coal Company 2 NSA Engineering, Inc
Highwall Mine Design Report June 2003