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Automated downhole monitoring at Southwest Harbor (WHS 2005)

Pilot testing of a permanganate injection system (WHS 2005)

Evaluating ASR using Columbia River water (WHS 2005)

Anatomy of a Sinking Chlorinated Solvent Plume (WHS 2003)

Comparison of Actual Evapotranspiration Estimates to a Soil Moisture Budget and Plant Growth (WHS 2003)

Hydrogeologic Characteristics of the Columbia River Basalts near Goldendale, Washington (WHS 2003)

Geology of the Brightwater Tunnel corridor (NGS 2004 / GSA 2003)

Abstract

Hydrogeologic Characteristics of the Columbia River Basalts near Goldendale, Washington

Presented at the 4th Annual Washington Hydrogeology Symposium, April 8–10, 2003, by Steven J. Stresky and Tim Flynn

Significant variations in hydrogeologic characteristics were observed during exploration to develop new groundwater supplies for the City of Goldendale. The hydrogeologic data obtained from the exploration wells, which penetrated the entire Wanapum Basalt sequence and the top of the underlying Grande Ronde Basalt, fills a data gap and improves the geologic understanding in an area of limited subsurface data in the Klickitat River basin. This paper reviews the exploration program and discusses an interpretation of the geology within the Columbia River Basalts (CRB) and its influence on groundwater conditions.

The first drilling site was approximately 5 miles south of Goldendale in Swale Creek Valley, a basin consisting of alluvial sediment overlying the Wanapum Basalt. Ample groundwater yield was discovered at the top of each of six Wanapum Basalt flows and the top of the underlying Grande Ronde Basalt. The top of the Ginkgo Flow revealed the most prolific yield in the basalt sequence. Water quality throughout the Wanapum as well as the Grande Ronde basalts was generally excellent and suitable for municipal supply. More commonly, poor water quality has been observed elsewhere in the limited number of explorations into the Grande Ronde Basalt.

The second drilling site was about 10 miles north of Swale Creek Valley on the southern flank of the Simcoe Mountains. A variety of volcanic deposits was encountered above the CRB, including competent basalt flows, vent-facies deposits, and lahars. A fluvial interbed was penetrated twice, suggesting a faulted sequence of deposits.

Exploration below the volcanic deposits in the Wanapum and Grande Ronde basalts revealed conditions very unlike those encountered in Swale Creek Valley. Flows were unusually thick, had poorly developed flow tops, and exhibited minimal yield. The Ginkgo Flow, thought to be regionally extensive, was absent. Groundwater yield from the Grande Ronde Basalt was sufficient, but the water quality was very poor.

The exploration has contributed to the understanding of hydrogeologic conditions relative to the basalts and geologic structure in the Goldendale area. The considerable contrast in aquifer yield and water quality between the two exploration sites is likely due to structural deformation, causing significant hydrogeologic variation over a relatively short distance. This variation has important implications to water supply development, evaluation of water rights, and watershed planning in the region.

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