Reconnaissance of hydrologic monitoring sites and preliminary monitoring plan for the Vale, Oregon, geothermal area

The Bonneville Power Administration is working with private industry to develop a geothermal demonstration project in the Known Geothermal Resources Area (KGRA) near Vale, Oregon. Hydrologic monitoring in the area is planned in order to evaluate any impacts from the proposed development. The hydrology in and around the Vale KGRA is not well known. Additionally, little is known about the targeted geothermal reservoir and the nature of its connection to the shallow ground-water system. Given this uncertainty, a variety of features were selected to ensure adequate monitoring coverage. Wells and springs in and around the geothermal area were evaluated, and 19 were selected as potential monitoring sites. In selecting wells and springs for monitoring, particular emphasis was placed on those with a known or probable connection with the geothermal system because they would most likely be the first to show any effects from development. The selected features include thermal wells in the hot-spring area near the town of Vale and a hot spring south of the KGRA. Several warm wells (70 to 90 degrees Fahrenheit) near the KGRA were also selected because it is likely that the water produced from these wells includes a component of geothermal water. In order to identify any effects of development, it is necessary to have an understanding of natural and man-caused variations and trends prior to development. A quarterly measurement schedule is proposed to help characterize these variations and trends. It is anticipated that the proposed monitoring plan will be modified as exploration and development proceed and more is learned about the geothermal system.