MODELING SUBSURFACE HEAT FLOW IN A BURIED VALLEY AQUIFER HYDRAULICALLY CONNECTED TO SURFACE WATER WITH GEOTHERMAL PUMPING

Geothermal heat exchange can be an efficient and cost effective method of heating and cooling. Open-loop systems involve extraction and surface discharge of groundwater. The pumping associated with this type of heat exchange has the potential to pull surface water into the underlying aquifer, a process that is not well studied. We have developed a three-dimensional numerical model to simulate fluid flow and heat transport and represent open-loop geothermal systems in a buried-valley aquifer hydraulically connected to surface water. Pumping is imposed at systematically varying distances from the river and depths below surface. The results produced by a homogenous permeability field are being compared to those produced by a realistic representation of the bimodal heterogeneity found in buried valley aquifers. The goal of this project is to gain insight into how heterogeneity and pumping scenarios affect the temperature of extracted water. A successful model would lead to a better understanding of basic relationships between hydraulics and heat flow in buried-valley aquifer systems, and could be used to improve design practices and optimize the efficiencies of open-loop geothermal systems at specific locations such as the Miami Valley Aquifer beneath Dayton, Ohio.