Lorenzo-Barreto, Pedro X.

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    Development of testbed for assessment of enhanced soil vapor extraction of trichloroethylene in unsaturated clayey soil
    (2014) Lorenzo-Barreto, Pedro X.; Padilla-Cestero, Ingrid Y.; College of Engineering; Harmsen Truckenbrod, Eric; Zapata López, Raúl E.; Department of Civil Engineering; Fernández Van Cleve, John
    Trichloroethylene (TCE) is a volatile organic compound (VOC) commonly found in many contaminated sites. It is a dense non-aqueous phase liquid (DNAPLs) considered harmful to human health. DNAPL pose particular threats because of their heterogeneous distribution and long-term perseverance in underground environments. Current remediation techniques for TCE in clay soil are extremely difficult and expensive. It is, therefore, necessary to develop an enhanced, cost-effective remediation technology that can be applied to those site contaminated clays. This project involves: development and testing of a testbed; conducting soil vapor extraction (SVE) experiments in the testbed; using cycled injections, and evaluating of experimental data. A laboratory-scale SVE testbed was developed, consisting of a stainless steel column packed with fine clay soil, fourth (4) soil vents, two (2) injection wells, and an extraction system. It is instrumented with transducer pressure sensors, flow meters, and sampling port. To evaluate the enhancement of SVE for the removal of TCE from unsaturated clayey soils by the addition of a capillary-based delivery of alcohol and brine solutions (methanol / CaCl2), SVE pilot study-experiments were conducted. Results from the SVE experiments were analyzed to determine the performance of the SVE methods to induce airflow and extraction of TCE vapors from TCE-contaminated clay soils. According to the results, the hydraulic behavior and extracted mass show reproducibility and consistency. Capillary-based delivery has proven to be a viable method to delivery reactant into clay soils of low permeability. Changes in pressure gradients suggest that the use of CaCl2 brine may increase air permeability of the system. The results from all the tests show that SVE can be used to extract TCE contaminants from clay soil; however, the removal is subject to mass transfer limitations, which reduce the efficiency of the extraction. Removal efficiency is between 33% and 53%, indicating that a large amount of initial mass still resides in the system and that total removal would take a long time. Measured temperatures through the soil bed during the extraction process indicate a significant variation in temperature. Lower temperatures under the extraction process are attributed to cooling effect of water in the system and TCE volatilization.