Summary of the Columbia Plateau Regional Aquifer-System Analysis, Washington, Oregon, and Idaho

Isotopically‐depleted late Pleistocene groundwater in Columbia River Basalt aquifers: Evidence for recharge of glacial Lake Missoula floodwaters?

“…Basalt flows within the CRB are columnar, dense in the interior with fractures and joints, and vesicular and porous at the top and bottom [Tolan et al, 2007]. Basalt flows are inter-bedded with Miocene sedimentary deposits typically consisting of clay, silt, sand, and gravels, and overlain by Pliocene to Holocene fluvial, glaciofluvial, eolian, and volcaniclastic sediments (collectively termed "overburden"), ranging in thickness from 15 to ∼180 m in the study area [Vaccaro, 1999;Bauer and Hanson, 2000].…”

Groundwater conditions during 2009 and changes in groundwater levels from 1984 to 2009, Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

“…The scope and objectives of this report are to characterize current (2009) groundwater conditions within each of the primary basalt aquifers and to evaluate changes in groundwater levels since the last regional synoptic measurement in 1984 (Whiteman, 1986;Vaccaro, 1999) through the presentation of maps of groundwater elevation and water-level change for the hydrogeologic units in the CPRAS. Regional assessment of water-level data from the CPRAS is necessary to document regional water-level conditions and to develop a broad view of the effects of groundwater development and management in the sustainability and availability of water supply in the region.…”

“…Overviews of the geology and hydrology of the Columbia Plateau presented in this section summarize detailed descriptions in reports that describe the groundwater flow system, including its boundaries, hydraulic characteristics, and components of recharge and discharge (Vaccaro, 1999); discuss the hydrology based on numerical modeling (Bauer and Hansen, 2000); and discuss the thickness, extent, and lithology of hydrogeologic units within the CPRAS (Kahle and others, 2009).…”

“…Therefore, the monitoring network data were supplemented with measurements from wells specifically selected for this study. Wells were selected from those measured during the 1984 USGS synoptic water-level investigation (Vaccaro, 1999) Information on land-surface elevation was needed to determine groundwater elevation from depth-to-water information. Land-surface elevations for many wells were provided by the agencies that measured the well.…”

“…These generalized water-level configurations are shown on plates 3-5 using color shading rather than elevation contours to indicate that the maps are simplifications of the large and complex actual flow system. Generalized directions of groundwater flow derived from this analysis and depicted on maps were modified on the basis of detailed maps of regional and subregional groundwater levels that better illustrate groundwater flow directions that are available for many parts of the CPRAS (Whiteman, 1986;Whiteman and others, 1994;Vaccaro, 1999;and Vaccaro and others, 2009).…”