ATES is used for storage of seasonal heat and cold. The stored thermal energy is usedfor indoor climate control and offers a great potential of saving fossil fuels. During the last two decades more than a 1000 ATES systems were implemented in The Netherlands. More recently, the national and municipal ambitions in reducing CO2 emissions provides a driving force for further rapid expansion. As retrofitting existing buildings with ATES systems is less cost-effective, ATES systems are mainly installed at greenfields or during the redevelopment of brownfields. Especially for the redevelopment of brownfields, questions arise on how ATES systems affect (residual) soil and groundwater contamination present. Especially, chlorinated DNAPL contaminants such as PCE (tetrachloroethene) and TCE (trichloroethene) can be present at the depths where ATES is commonly applied (>depth of 20 m below ground level). At these depths biological degradation processes generally result in slow reduction of contaminant plumes. The elevated ATES temperatures (up to 40 oC) as well as the mixing of groundwater in these systems, could create “win-win” conditions by offering potential for increased contamination remediation. However, there may also be increased risk of contaminant mobilisation and dissolution. Hydrochemical transport modeling using PHT3D showed that the remediating effects and potential environmental risks depend on the rates and kinetic model used for degradation, as well as on the hydrogeological conditions and contaminant distribution. Reliable estimates on DNAPL present near the planned ATES wells and contaminant degradation potential in the aquifer showed to be essential for risk-assessment of the ATES application in contaminated aquifers. Based on these modelling results and field observations at ATES systems, a framework was developed for the assesment of site-specific conditions required for net beneficial effects of ATES systems in contaminated soils and groundwater.
