Reactive Transport Modeling of Thermal Column Experiments to Investigate the Impacts of Aquifer Thermal Energy Storage on Groundwater Quality

Abstract

Aquifer thermal energy storage (ATES) systems are increasingly being used to acclimatize buildings and are often constructed in aquifers used for drinking water supply. This raises the question of potential groundwater quality impact. Here, we use laboratory column experiments to develop and calibrate a reactive transport model (PHREEQC) simulating the thermally induced (5-60 °C) water quality changes in anoxic sandy sediments. Temperature-dependent surface complexation, cation-exchange, and kinetic dissolution of K-feldspar were included in the model. Optimization results combined with an extensive literature survey showed surface complexation of (oxy)anions (As, B, and PO4) is consistently exothermic, whereas surface complexation of cations (Ca and Mg) and cationic heavy metals (Cd, Pb, and Zn) is endothermic. The calibrated model was applied to simulate arsenic mobility in an ATES system using a simple yet powerful mirrored axi-symmetrical grid. Results showed that ATES mobilizes arsenic toward the fringe of the warm water bubble and the center of the cold water bubble. This transient redistribution of arsenic causes its aqueous concentrations in the cold and warm groundwater bubbles to become similar through multiple heating cycles, with a final concentration depending on the average injection temperature of the warm and cold ATES wells.

Using Heated Column Experiments to Investigate the Effects of In-Situ Thermal Recovery Operations on Groundwater Geochemistry in Cold Lake, Alberta

“…In addition, Si concentrations were likely influenced by the lower Fe 2+ oxidation rate and subsequent discontinuation of silica-ferrihydrite coprecipitation. Bonte et al (2014) indicate that sorption of Si also decreases with increasing temperature, and supports the observations made in the anaerobic phase of Experiment 2.…”

“…Although this expression can adequately explain sorption mechanisms with respect to some sorbed species such as arsenic, it does not necessarily apply for all dissolved species, as demonstrated by the studies involving nickel. As an alternative to using the formula above, temperature-dependent surface complexation modelling (TD-SCM) is an emerging method to better understand sorption mechanisms, which has demonstrated its success when simulating surface interactions with arsenic and some cations over a range of temperatures (Bonte et al, 2014;Van Breukelen and Bonte, 2016).…”

“…Several studies have recently examined and reviewed the geochemical effects from ATES systems in Belgium and the Netherlands through a combination of field programs, column experiments, and geochemical modelling. Bonte et al (2011Bonte et al ( , 2013aBonte et al ( , 2013bBonte et al ( , 2013cBonte et al ( , 2014 has published extensively on this subject and the effects of ATES on the evolution of groundwater geochemistry. Over the course of a 4-year field monitoring period, the observed concentrations of Cl, SO 4 , NO 3 , NH 4 , Fe, Mn, and DOC from groundwater at shallow and deep ATES warm well locations showed a cyclical behavior which generally followed the increasing and decreasing trends in temperature and pumping/injection rate (Bonte et al, 2013a).…”

“…In conjunction with the field program, laboratory column experiments were also performed by Bonte et al (2013aBonte et al ( , 2013bBonte et al ( , 2013cBonte et al ( , 2014 to assess the impact of temperature on groundwater quality and geochemical changes. The tests were conducted at 5°C, 11°C, 25°C and 60°C in anoxic conditions using three different aquifer sediment cores and carried out over a period of 24 pore volumes (equal to one pore volume per day).…”

Groundwater temperature anomalies in central Europe

“…[5,6,[78][79][80]). In some urban areas, where aquifers are already contaminated with heavy metals and organic compounds, an increase of GWT by only 5K might also entail a decrease of dissolved oxygen and may lead to a mobilisation of other contaminants such as arsenic [81][82][83][84]. Nevertheless, elevated GWTs provide the opportunity to harness more energy from the aquifer using shallow geothermal systems or make the operation of such systems more efficient [56,[85][86][87][88].…”