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Mountain Coal Company- West Elk Mine <br />Sylvester Gulch Road Geotechnical Investigation <br />Seismic Refraction Survey <br />Summary of Operations <br />• 23+00 <br />A three layer proSle best descnbes the data from the seismic refraction line at 23+00 (Figure 6). The <br />velocities of the first and second layers are typical of unconsolidated sedime~s. Velocity and sWchue of <br />the third layer is represe~ative of geologic properties of weathered bedrock, possibly sandstone. <br />7+m Syylvester Qiloh Seisms Lf~re 23+00 <br />r+eo _...._. ._ --_. ..--~ -- ----.. _____..._.---. ._..__.__.. _..~---~irE <br />~+so ... _.. _ _ - _ _ .. _. _.... _ _._ _..._~ _ ~ ~ <br />_ . S <br /> Hr <br />~+w a+. _.. __ - _ - - <br /> ~ ma <br />e+s <br />4i <br />»ao <br /> <br />g .. ... __ . ..... <br />_ _ .. <br />~ _ _ ._ <br />us un <br />o~+zo <br /> <br />- ._ _ _ _ <br />~~ V1=975ff/s- ...°.e_.e~.. ys-oo- ~+om~ - ~-o a+a .. <br />o s <br /> &t? <br />aka <br />a r+m ~ <br />_ _ _ _... _ <br />_.. - <br />„oo _ _ _ - -- - ___ _ _- -- <br /> V2 =3275 tt/s <br /> <br /> -a-Ground Surface <br /> - __ <br />- Bo+mdary 1 _ V3 - 787a Rls <br />'aro -Boundary2 _-- _. _. <br /> <br /> o . +o m so ao so eo ~o eo ra +m no +m +m +w +so +eo +~o +so +eo aw z+o zzo zso zeo zso x o <br /> wctance ryq <br />Figure 6. Seismic refraction profile at 23+00. <br />Higher velocities of the second layer could be associated wRh the thin sandstone cobble layer found in the <br />• borehole at 8 feet (Figure 7). Given the similarities in velocity and struchire to what was found in lines <br />17+00 and 19+00, this is a reasonable interpretation. Near the borehole, seismic refraction data indicates <br />a third layer at a depth of 42 feet. Borehole data indicates a sandstone cobble layer ai 31.5 feet. Because <br />the velocity for the third layer in line 23+00 is substarrtially higher than velocities attributed to a <br />consolidated sandstone cobble layer in lines 17+00 and 19+00, it is more likely that the velocity of the <br />third layer in line 23+00 is a result of a competed weathered bedrock unit, probably sandstone. <br />• <br />UMS, Inc, Page 5 05/17/03 <br />