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Abstract: The U.S. Department of Energy Big Sky Regional Carbon Sequestration Partnership completed drilling the world’s first continental flood basalt sequestration pilot borehole to a total depth (TD) of 1253 m at a paper mill site near the town of Wallula located in Southeastern Washington State. Site suitability was assessed prior to drilling by acquisition, processing and analysis of a four-mile, five-line, three component seismic swath, which was processed as a single data-dense line. Analysis of the seismic survey data indicated absence of major geologic structures that would preclude CO2 injection at the site. Drilling of Wallula pilot borehole was initiated on January 13, 2009 and reached TD on April 6, 2009. Hydrogeologic information was obtained primarily during borehole drilling/advancement utilizing a progressive drill-and-test characterization strategy. A general decreasing transmissivity trend with depth pattern was observed, which is consistent with results exhibited for Columbia River basalt interflow zones at a number of other deep wells in the region. Based on the comparative results from 10 test intervals, a candidate injection test zone was identified between the general depth interval of ∼828 and 875 m bgs. Over this interval, three brecciated interflow zones were intersected and isolated for CO2 injection. The flow tops have moderate permeability (75 to 150 millidarcies) and are bounded by thick flow interiors that have extremely low (microdarcy) permeability. The borehole configuration established at the Wallula pilot site provides a unique opportunity to scientifically study the reservoir behaviour of three connected reservoir intervals confined between primary and secondary caprock zones. The permitting process for the CO2 injection has proceeded in accordance with formal rules for geologic sequestration projects enacted in June 2008 into the underground injection control program administered by the Washington State Department of Ecology. The permitting process is expected to conclude in October 2010 and injection would begin soon thereafter. Post-injection monitoring includes long-term sampling of water retrieved from the injection zone, shallow groundwater and soil gas monitoring, and PSInSAR. [Copyright &y& Elsevier]