Effects of Groundwater Heat Pump Systems on the Temperature and Quality of Groundwater in Recharged Aquifer

Abstract

Groundwater heat pump (GWHP) systems in three different hydrogeological fields, Beijing were selected, and their effects on temperature of groundwater in recharged aquifer were researched for three years. Results showed that the degree of thermal breakthrough was controlled by the distance between pumping wells and injection wells, and the temperature of groundwater with high flow rate can recover to normal faster than those with low flow rate. When distance between pumping wells and injection wells were shorter than 30m, thermal breakthrough may happen and the variation range of groundwater temperature during one heating or cooling period was 8~12°C.However, thermal breakthrough can be negligible and the temperature of groundwater may be steady when the distance between those wells was longer than 50m. Furthermore, GWHP in two different hydrogeological fields were selected to observe their effects on groundwater quality for one year. One GWHP was situated on the northwest piedmont alluvial fan of Beijing and the other was located in the southeast plain area of Beijing. Groundwater was sampled from those fields and thirty-two inorganic components were analyzed. Heavy metals were not detected, and calcium, magnesium, chloride, sulfate, fluoride and other ten inorganic components were studied. Groundwater quality in the northwest of Beijing was relatively steady because that aquifer was in relative oxidation environment. However, groundwater quality in the southeast of Beijing was subject to change because that aquifer was in relative reduction environment. Nitration reaction happened in the plain area, and ammonia, nitrite converted into nitrite nitrogen and nitrate nitrogen, respectively. Simultaneously, pH, concentrations of iron and manganese decreased, and total hardness increased.