As part of the new navigation lock for Bonneville Dam a new water source for the Bonneville Fish Hatchery must be supplied. The hatchery is located on the Oregon side of the Columbia River downstream of the dam. It requires large quantities of water free from chemical and biological contamination. In addition, the water has to be in a narrow temperature range. Currently the fish hatchery receives its water from a well field that is located on the alluvial terrace downstream of Bonneville Dam. The well field lies in the proposed approach channel for the new lock and has to be abandoned during construction of the lock. For the continued water supply of the hatchery, a new well field will be developed north of the approach channel. Early in the planning phase for the new lock, concerns were raised about the potential impact of the relocation of the well field and the excavation of the new approach channel on the hatchery. To assess these concerns and to assure a continuous water supply during and after construction, a hydrogeologic investigation was initiated. Within the framework of the investigation this study focuses on the analysis of pumping test data and the development of a three-dimensional ground water flow model for the site.
In the first phase of the study, data from eight pumping tests were analyzed. Hydrogeologic properties of the sedimentary units that make up the downstream terrace were determined. The focus was the pre-slide alluvium (PSA) aquifer, the water source for the existing and the future well field. In addition, the nature and location of hydrogeologic boundaries for the ground water system were determined. The results, in conjunction with information from subsurface exploration and laboratory tests, were used to develop a conceptual understanding of the ground water system at the site. The PSA aquifer receives its recharge primarily from leakage through the overlying confining layers over a large area. A direct connection between the Columbia River and the PSA aquifer could not be detected. They appear to be separated by a continuous aquitard layer or by a layer of fine-grained sediments on the river bottom.
Based on these findings, in the second phase of the study, the ground water modeling program HST3D (Kipp, 1987) was used to develop a three-dimensional ground water model for the site. The model was calibrated with data from one of the pumping tests. The calibration was then verified with a second set of conditions including pumping from shallow and deep wells. Water levels in the deep PSA aquifer and the shallow unconfined aquifer were successfully matched. A satisfactory match of observed conditions was possible with only slight modifications of the hydrogeologic parameters determined by pumping test analysis and based on the conceptual model developed in the first phase of the study. It appears that a continuous aquitard layer separating the Columbia River and the PSA aquifer, with the aquifer receiving recharge through vertical leakage over a large area, is a valid representation of the aquifer system.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5036 |
| Date | 01 January 1990 |
| Creators | Baron, Dirk |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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