Geochemical Study of Groundwater in the Sho River Fan, Toyama Prefecture for Heat Usage by a Geothermal Heat Pump

Chemical and isotopic (D, O) compositions of 56 water samples from the Sho River fan, Toyama, northern part of central Japan, were analyzed to examine their water quality, origins, and water flow for geothermal heat extraction used for air-conditioning and melting of road snow by a geothermal heat pump (Geo-HP). Groundwaters are a mixture of two big river waters (Sho and Oyabe) and precipitation. Deep groundwaters from observation wells are characterized to be high in pH and enriched in HCO3 compared to the shallow groundwaters. These features may indicate that the shallow groundwater originated from a mixture of river water and precipitation moving to the north and becoming confined due to the presence of an impermeable layer. Groundwaters attain high pH due to ion exchange reactions with rocks containing clay minerals, where HCO3 concentration also increases.