Simultaneous Acquisition Of P- And S-Wave Crosswell Seismic Profiles In A Contaminated Basalt Aquifer

Multiple seismic crosswell surveys have been acquired by LBNL in a fractured basalt aquifer<br>at Idaho National Engineering and Environmental Laboratory (INEEL). Most of these surveys<br>used a high frequency piezoelectric seismic source to obtain P-wave velocity tomograms.<br>Additionally, we deployed a new type of borehole seismic source, know as an orbital vibrator, in<br>a crosswell seismic survey as part of the subsurface characterization program at this<br>contaminated groundwater site. This source, know as an orbital vibrator, allows simultaneous<br>acquisition of P- and S-waves. The orbital vibrator was developed for oil field applications and,<br>to our knowledge, this is the first environmental scale crosswell application. Both velocity and<br>attenuation tomograms have been calculated. The velocity tomograms show a relationship to<br>contaminant propagation in the groundwater (as measured by logs and cores). Zones of high<br>contaminant flow are consistent with zones of low velocity (both P- and S-wave) and high<br>attenuation. We believe horizontal fracture zones at the boundaries of basalt flows are<br>controlling the contaminant flow and the seismic properties. Additionally, high amplitude guided<br>waves are observed and we believe these waves delineate thin (l-2 m) zones of velocity contrast<br>which relate to fracturing and, in some instances, coincide with contaminate flow.