The U.S. Geological Survey (USGS) has begun a study of the Columbia Plateau Regional Aquifer System (CPRAS) with the broad goals of: 1) characterizing the hydrologic status of the system, 2) identifying trends in ground-water storage and use, and 3) quantifying ground-water availability. This study is one of several ongoing regional assessments being conducted as part of the USGS Ground-Water Resources Program.

The Columbia Plateau Regional Aquifer System covers over 50,000 square miles of eastern Oregon and Washington and western Idaho. The primary aquifers are basalts of the Columbia River Basalt Group and overlying basin-fill sediments. Ground-water availability issues in the basin include: 1) widespread water-level declines caused by pumping, 2) reduction in base flow to rivers and associated effects on temperature and water quality, and 3) effects of global climate change on recharge, base flow, and ground-water availability.

The major elements of the approach include:
1) Documenting changes in the status ground-water resources.
2) Quantifying the hydrologic budget for the system for current and past conditions.
3) Updating the regional hydrogeologic framework for the basalt and basin-fill aquifers.
4) Developing a ground-water flow simulation model for the system.

The simulation model will be used to evaluate and test alternative conceptual models and later to evaluate ground-water availability under alternative development and climate scenarios. The project began in October 2007 and is scheduled to be completed in 2011. We will present a summary of the current status of the study and some early findings.