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Hydrogeologic Characterization of Dutch Canyon, Scappoose, Oregon

D. L. Wagner
Portland State University

Dutch Canyon is located in Columbia County, Oregon and has poor groundwater yields, locally saline water, and no previous hydrogeologic studies. This study identified the aquifers in Dutch Canyon and characterized water quality. The physical hydrogeology was primarily assessed through the collation of 196 well reports. Unit parameters were estimated using pump rates and drawdowns. Water quality was assessed through the collection of well, spring, and stream water, analyzing for major ions, stable isotopes, and field water quality parameters.

The units of Dutch Canyon were separated into five hydrostratigrapic units: the lower, middle, and upper units of the Miocene Scappoose Formation, and the overlying Wapshilla Ridge and Ortley members of the Miocene Grande Ronde Basalt. The Scappoose Formation units are fine-grained and limit the useable aquifer volume and vertical movement of groundwaters.

Geochemically, the lower units of the Scappoose Formation were similar, with groundwater high in total dissolved solids (mean TDS = 330 mg L-1; n = 27). Nearly 20% of the wells yielded groundwater exceeding the U.S. Environmental Protection Agency’s National Secondary Drinking Water Regulation standard of 500 mg L-1 TDS. The overlying units yield water with lower TDS (mean < 200 mg L-1; maximum = 342 mg L-1; n = 20).

The primary water quality concern is saline water, which is generally found in the lower units of the marine Scappoose Formation, from diluted connate water. Low recharge is consistent with the geology and steep terrain and limit the available groundwater and degree of flushing of connate waters.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013