POTENTIAL FOR INSTALLING GROUND SOURCE HEAT PUMPS IN WISCONSIN BASED ON THE CHEMISTRY OF GRANITIC BEDROCK

Geothermal energy is one of the emerging forms of alternate energy. This form of energy is mostly used to generate electricity, constrained by geothermal gradient where there is an adequate amount of heat energy near the surface. Another use for geothermal energy is to heat or cool individual buildings through ground source heat pumps or GSHPs, potentially cheaper and cleaner than using natural gas for heating buildings. The heat is commonly captured and transferred through water to produce usable energy. Heat generating radioactive elements, such as uranium, thorium, and potassium, help supplement the geothermal gradient by producing radiogenic heat. Presence of those elements in sufficient quantities in granitic bedrock close to surface can potentially reduce the cost of GSHP installation. My research is focused on determining the uranium, thorium, and potassium content of granitic rock samples from Marathon County, Wisconsin, with the aim of determining the most suitable locations for installing GSHPs based on the concentrations and relative abundance of those three elements with depth. Preliminary results from analyzing seventeen samples collected from 30 to 304 meters depth using Inductively Coupled Plasma Optical Emissions Spectrophotometer (ICP/OES) show presence of high amounts of radiogenic elements. Potassium has an average of 3.5 weight percent throughout each sample, and is consistent throughout each analyzed depth. Uranium ranges from 5 to 10 ppm on average, with the highest concentration occurring at depths of 90 to 150 meters. Thorium ranges from 18 to 26 ppm on average, with the highest concentrations occurring at the same depth as uranium. Here we present our sample locations, analytical methods, and implications of our results for identifying suitable locations for GSHP installation in Marathon County, WI.