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OxBow Coal Mine <br />Geotechnical Investigation <br />Seismic Refraction Survey <br />Summary of Operations <br />The recorded seismic data are processed and interpreted using acommercially-distributed software <br />package. The traveltimes to the refracted events or "first breaks" are plotted and the subsurface velocities <br />are determined. When the traveltimes and velocities are known, the depth to bedrock can be calculated <br />(Figure 4). The seismic refraction method has an effective depth of investigation that ranges between 10 <br />and 200 feet, depending on survey source size, line lengths and geophone spacing. <br />-i6 <br />-i~ <br />-n <br />_p <br />23 <br />I6 <br />_~ <br />33 <br />36 <br />Fig. 4. buerpreted section <br /> <br />• <br />UMS, Inc. Page 2 07/09/03 <br />