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Mountain Coal Company-West Elk Mine <br />Sylvester Gulch Road Geotechnical Im+estigation <br />Seismic Refraction Survey <br />Summary of Operations <br />• the digital data for later retrieval and pried a paper tet~rd as a backup record of each shot Figure 1 <br />illustrates atypical seismic refraction sex. <br />Figure 1. Typical seismic refraction set. <br />~a~. tea.., <br />s• t~0' - 10' s' s 10' <br />~~ <br />~' 0 ~ <br />91 -~~ T P ~ T <br /> <br /> <br />Survey Hne <br />SELSNIIC REFRACTION SURVEY RESULTS <br />Survey results far each line are presented in a sequerdial manner starting with the line at 17+00 and <br />ending with the line at 49+25. Included in survey results for each line are: <br />• Apparent depth to each geologic acoustic impedance boundary <br />• Derived subsurface profiles based on processing and interpretation of acquired seismic data <br />• Apparel. velocities for two and three layer sub-terrain models <br />• hRerpretations of geologic layers based on seismic refraction first arrivals, scatter characteristics, <br />ai geatechniral borehole data. <br />A s+++++++~*y of the interpreted results for each seismic refraction line is presented below. Data quality for <br />the survey was excellent, and results agreed well with geotechnical borings, geomorphology, and local <br />geology. Bedrock was consistently detecxed and mapped in all the profiles using atwo-layer and <br />occasionally three-layer model. In some caste the beneath the steeply sloping terrain, a lateral variation <br />in bedrock occurred, say from a shale or claystone horizon in the center of the profile, to a sandstone <br />bedrock further up the steep flanks. This lateral unconformity, hkely due to an earlier episode of <br />channeled scouring that was later buried, is referred to as asub-cropping and resuhs in a lateral velocity <br />contrast along the bedrock coNact, complicating the seismic interpretation. However, scatter in emergem <br />seismic rays provided an indication of when this was occurring and geotechnical boring data invariably <br />• backed up the interpretation. For this analysis a single average bedrock velocity was used to process the <br />data and profile the bedrock contact. Actual depth to bedrock may vary by +/- 15% in areas of sub- <br />cropping occurrence, shale bedrock being slightly deeper and sandstone slightly shallower, however, for <br />the purpose of this investigation the processed results are sufficient. Subseque~ analysis and further <br />processing may be performed to reline depth data if deemed necessary. <br />UMS, Inc. Page 2 05/17/03 <br />