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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 />_~ <br />-m <br />-u <br />-n <br />10 <br />13 <br />16 <br />_~ <br />31 <br />_~ <br />Fig. 4. /nterpreted section <br />• <br />C <br />UMS, Inc. Page 2 07/Oy/03 <br />