Adjoint Simulation of Heat Transport in Groundwater

The injection of heated water into an aquifer produces a thermal plume that travels through the aquifer. If the aquifer contains temperature-sensitive receptors, such as an extraction well for drinking water or cooling water, or a discharge point that feeds a temperature-sensitive ecosystem, the location of the injection point should be chosen to ensure that the groundwater temperature at the receptor does not increase by more than an allowable threshold. The adjoint method is an efficient tool for identifying allowable injection points. In the adjoint method, information is propagated upgradient, against groundwater flow, from the receptor to all possible injection locations. Thus, the results of one adjoint simulation can identify all possible injection locations for which the temperature change at the receptor would remain below the threshold. This work demonstrates the use of the adjoint method for identifying allowable injection points of heated water.