Assessment of thermal heating for the removal of chlorinated solvents from fractured bedrock

摘要

The aim of this study was to assess the performance of thermal heating for the removal of chlorinated solvents from fractured rock. The study included a laboratory experimental program, a field pilot study demonstration and a mathematical modeling component. In the laboratory experimental program, thermal heating parameters, such as operational temperature, heating duration, and the corresponding degree of contaminant removal, were evaluated through a series of heating tests. To evaluate the effect of heating temperature and heating duration on the degree of contaminant mass removal, two different heating profiles were utilized during the experiments. Additionally, seven types of rock and two common contaminants were selected to evaluate the effect of thermal heating on different geological media impacted with different chlorinated compounds. In general, results showed that heating duration had the most significant effect on the degree of contaminant mass removal in post-remedy samples. Results showed that a higher porosity in combination with a lower organic content facilitates the removal of chlorinated solvents from the rock matrix. A Thermal Conductive Heating (TCH) pilot test was implemented by TerraTherm, Inc. at the former Naval Air Warfare Center (NAWC) in West Trenton, NJ to assess the performance of TCH for the removal of trichloroethylene (TCE) and daughter products (i.e cis-1,2-dichloroethylene (DCE) and vinyl chloride (VC)) from fractured bedrock. Results showed that treatment removed 318.5 kg of TCE, DCE and VC, from the treatment zone, of which 62.6 kg were recovered from the rock matrix. A total of 63 % TCE, 65.8 % of DCE and 90.4% of VC were removed during heating. Finally, Semi-analytical solutions were derived to evaluate back diffusion in a fractured bedrock environment where the initial condition comprises a spatially uniform, non-zero matrix concentration throughout the domain. It was concluded that the time required to reach a desired fracture pore water concentration is a function of the distance between the point of compliance and the upgradient face of the domain where clean groundwater is inflowing. Hence, shorter distances correspond to reduced times required to reach compliance.