2-D PHYSICAL MODELS OF THERMAL CONDUCTION HEATING FOR REMEDIATION OF DNAPL SOURCE ZONES IN AQUITARDS

In-situ thermal remediation (ISTR) technologies are receiving increasing attention for remediation of dense non-aqueous phase liquid (DNAPL) source zones in soil and groundwater. A clear understanding of the primary mechanisms of ISTR is crucial to enable selection of appropriate sites and effective ISTR technologies for DNAPL source zone remediation. Thermal conductive heating (TCH) coupled with vapor extraction is an ISTR method that takes advantage of the invariance of thermal conductivity across a wide range of soil types to effect treatment of DNAPL in lower-permeability and heterogeneous formations. Under the sponsorship of the U.S. Strategic Environmental Research and Development Program (SERDP), bench- and larger-scale remediation experiments are being conducted at the facilities of VEGAS - the Research Facility for Subsurface Remediation at Universitat Stuttgart, Germany to better understand the principal mechanisms that control TCH performance in the saturated zone. In parallel, a numerical model was optimized based on the experiments. This paper reports the results of various 2-D experiments that we completed, while the companion paper (Hiester et al. 2008) focuses on the related 3D experiments. A series of small-scale two-dimensional (2-D) experiments were carried out at VEGAS. The aim of these experiments was to investigate the principal processes of TCH in layered, saturated materials. The experiments were conducted in a stainless steel two-dimensional flume with the dimensions of 1100 mm [width] x 740 mm [height] x 85 mm [thickness]. The front panel consisted of a steel plate for homogeneous heating experiments, and Pyrex ® glass for the remediation experiment. The flume was equipped with 100 Pt-100 discrete temperature sensors (10 rows x 10 columns) to measure the temperature distributions while heating to steam distillation temperatures, 100 °C. Additionally, an infrared camera was used periodically to obtain continuous temperature distributions during the remediation experiments, in which a known amount of tetrachloroethene (PCE) was released prior to heating. During heating, the mass of contaminant collected in the extracted gas was monitored. Following heating, soil samples were collected to estimate the mass of contaminant remaining in the soil. The main TCH contaminant removal mechanism within the saturated porous media was vaporization. Nearly complete DNAPL removal from the source zone was accomplished by this method. No DNAPL