Strategy and sequencing of hydrologic characterization of the Columbia River basalts

Development of strategy to provide specific information on a geologic medium, for which the conceptual hydrologic system is, initially, unknown or poorly understood, requires thoughtful planning and sequencing of tests. In southeastern Washington, the sponsorship of the National Waste Terminal Storage Program (of the US Department of Energy) has provided a significant opportunity to further the conceptual understanding of Columbia River basalts hydrology. The Basalt Waste Isolation Project has prepared a strategy for field characterization of the basalts which involves four major phases of field investigation; reconnaissance investigations, hydraulic head baselining, large-scale hydraulic testing, and underground tests. The paper will provide a brief description of the type and purpose of the investigations associated with each phase and the general rational underlying the approach to these hydrologic characterization activities. In particular, the manner by which information from earlier phases of the investigation is used to plan and prepare for later phases is discussed. Examples will be provided which illustrate the data reduction performed on reconnaissance-level transmissivity data, the use of natural transients in hydraulic head to obtained preliminary estimates of hydraulic properties, and the opportunity of using drilling stresses to design large-scale tests and to predict performance