Temperature influence on the NAPL-water interfacial area between 10 °C and 60 °C for trichloroethylene.

ABSTRACT

Underground thermal energy storage (UTES) can contribute to renewable energy usability, especially in urban areas with the most demand and available infrastructure. But UTES may interact in those areas with non-aqueous phase liquids (NAPL) by increasing the temperature in storage formations. To determine temperature effects on NAPL dissolution rates into groundwater, the effective specific interfacial area (anw) between trichloroethylene (TCE) and water, as a function of temperature and TCE pore saturations, was calculated. The interfacial tension between the flushing solution and the NAPL, the adsorption coefficient and the retardation of a reactive tracer were determined by the drop weight method and interfacial tracer tests at 10 °C, 30 °C and 60 °C. From 10 to 60 °C anw increased by a factor of six to eight. Based on the results, a function to describe the anw between TCE and water was developed, which could improve numerical models on NAPL dissolution rates. The main mechanisms for the increase in anw are suggested to be NAPL blob migration on pore scale, and thermal-induced changes in wettability and in blob shape correlating with a temperature-induced decline in effective porosity of up to 32%. These results contribute to the understanding and predictability of UTES in contaminated aquifers, the general response of NAPL behavior on artificial increasing aquifer temperatures and the improvement of thermal and other groundwater remediation techniques.