In 2009, the U.S. Department of Energy’s Big Sky Regional Carbon Sequestration Partnership completed drilling the first carbon dioxide (CO2) sequestration pilot borehole well with continental flood basalts, to a total depth of 4110 ft at the Boise Inc. mill property at Wallula, Washington. As part of the characterization program, hydrologic tests were conducted on selected basalt interflow reservoir zones and flow-interior/caprock intervals during, and at the completion of the borehole drilling activities, to support selection of a candidate injection reservoir for subsequent CO2 sequestration studies. Based on the results obtained during the active borehole characterization program, an injection reservoir was identified between the depth interval of 2716 and 2910 ft that contained three individual Grande Ronde Basalt breccia interflow zones. The Wallula pilot well injection reservoir lies stratigraphically below the massive Umtanum Member of the Grande Ronde Basalt, whose flow-interior section possesses regionally recognized low-permeability characteristics.

Following well completion activities that occurred during May 2009, Wallula pilot well injection reservoir zone pressure was monitored for an extended period (i.e., between June 2009 and December 2010) for the purpose of evaluating seasonal and temporal reservoir pressure dynamics in response to natural and manmade-related stresses. Following completion of the baseline pressure monitoring phase, a series of hydrologic well tests were conducted to assess possible impacts to the injection reservoir due to previous well completion activities, and for determining large-scale hydraulic property and hydrologic boundary detection. Results for the characterization program conducted during the initial, active borehole drilling campaign were previously published in McGrail et al. (2009).1 This report presents the hydrologic test results obtained following well completion, during the subsequent baseline monitoring period, and recent well testing phase of the characterization program. Recommendations are also provided to reduce the uncertainty concerning operative conceptual conditions within the candidate CO2 injection horizon.