EVALUATING THE IMPACTS OF A CLOSED-LOOP GROUNDSOURCE GEOTHERMAL SYSTEM AT BALL STATE UNIVERSITY ON SUBSTRATE AND GROUNDWATER TEMPERATURES IN PHASE 1

Ball State University (BSU) began installing the nation’s largest ground-source geothermal project in 2009. During Phase 1 of the BSU geothermal conversion, 1,803 geothermal boreholes were drilled 400 ft deep in a 15x15 ft grid in two large fields (North and South) in the northern part of campus. Two geothermal exchange loops were installed in each borehole to add or remove heat from the ground to moderate the temperature in buildings. Students and faculty collected hydrogeologic and temperature data from a series of groundwater monitor wells beginning Summer 2010. An additional 600 500-ft deep geothermal boreholes with single exchange loops are now complete in the Phase 2 field location and we will begin to gather hydrogeologic information on the Phase 2 field in five nested wells surrounding that site.

Despite the rise in community-scale ground-source geothermal energy systems, there is little empirical information on their effects upon the groundwater environment or the effects of the groundwater flow environment on the geothermal field. Previous studies have triggered concern over the impact of large-scale geothermal systems where there were documented increases in groundwater temperatures. Since BSU initiated Phase 1 in late November 2011 with cold-water circulation (adding heat to the ground), data indicate that the ground temperature has increased over 10 degrees Celsius in the center of the South Field, with temperatures rising in other surrounding monitoring wells depending on their distance from the edge of the geothermal boreholes. Maintaining a temperature differential between the fluid inside the exchange loops and the geologic substrate and/or groundwater outside of the loops is crucial to the efficiency of the systems, which are typically designed so that temperatures will not increase or decrease considerably over the years. The temperature increases are distinctively different in the upper highly hydraulically conductive aquifers and the lower poorly conductive formations. The overall ground-source geothermal system will continue to influence and be influenced by the stratigraphy and hydrogeologic transmissivity.