Graduate Thesis Or Dissertation
 

A hydrogeologic study and groundwater model of Parrett Mountain, Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5138jj16m

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  • This thesis presents a hydrogeologic study of the Parrett Mountain Region, located approximately 20 miles south of Portland, Oregon. The aim of the study was to investigate the impacts of Columbia River Basalt on the regional groundwater system, to expand our understanding of flow through fractured basalt, to improve management practices in the area, and to provide local detail for a regional groundwater model being developed by the USGS. An equivalent porous medium model with steady state heads was developed of the area using MODFLOW, a finite difference method for modeling groundwater flow. The data used to develop the model included (1) geologic stratigraphy of the area; (2) time averaged 1995-1996 water level data; and (3) local hydraulic properties measured by aquifer pump tests. Based on the hydrogeologic study we determined that using a continuum approach was the most appropriate method for modeling the flow system. We also found that during model calibration no faults were necessary to reach calibration goals, suggesting that faults do not play a significant role in regional groundwater flow at steady state. Finally, based on available data, we were unable to determine the role of basalt flow tops on groundwater flow. By using the calibrated flow model the impact of projected population increases were investigated to aid in groundwater management practices. Based on assumptions of uniform population increases and a uniform pumping distribution, it was found that an increase of approximately 8,000 people would result in drawdown estimates of less than 2 meters throughout the model.
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