Degradation of carbon tetrachloride in a reducing groundwater environment: implications for natural attenuation |
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| Institution: | 1. Geomega, 2995 Baseline Road, Suite 202, Boulder, CO 80303, USA;2. Chevron Environmental Management Co., 6001 Bollinger Canyon Road, San Ramon 94583, USA;3. Synthetic Intermediates Ltd. St Andrew''s Court, Nantwich, Cheshire, CW5 8PZ, UK;4. GeoAlpha International, Suite 304, 7 Avenue Georges Pompidou, 92593 Levallois-Peret, France;1. Department of Civil Engineering, Building 118, Technical University of Denmark, 2800, Lyngby, Denmark;2. Department of Contaminated Sites & Groundwater, Orbicon, Linnés Allé 2, 2630, Taastrup, Denmark;3. Centre for Regional Development, Capital Region of Denmark, Kongens Vænge 2, 3400, Hillerød, Denmark;4. Department of Waste & Contaminated Sites, COWI, Parallelvej 2, 2800, Lyngby, Denmark;1. Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan;2. Bioenvironmental Engineering Department, Chung Yuan University, Chung Li, Taiwan;3. Deaprtment of Biological Science, National Sun Yat-Sen University, Kaohsiung, Taiwan |
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| Abstract: | Several laboratory experiments have demonstrated degradation of carbon tetrachloride (CT) in groundwater, but there appear to have been no corroborating long-term field studies. Investigations conducted in 1989 and 1999 at an industrial site constructed on an infilled estuarine environment in France provide data over a decade for which CT degradation could be evaluated. A Dense Non-Aqueous Phase Liquid (DNAPL) containing oil and >90% CT that was present in 1989 was absent in the extremely reducing site groundwater in both 1999 and 2000 (average Eh=?170 mV at pH 7, sulfide up to 21 mg l?1, and Fe+2 up to 3.2 mg l?1). These conditions facilitated dechlorination of CT to chloroform (CF) present at up to 46 mg l?1, and methylene chloride (up to 75 mg l?1). Carbon disulfide (CS2), a terminal degradation product in reducing environments in laboratory experiments, was present at a mass ratio averaging 2.4:1 CF:CS2, indicative of abiotic degradation. The lack of detection of the separate phase CT, the ratio of CF:CS2, the presence of low molecular weight organic acids (i.e., acetate ～900 mg l?1; citrate 360 mg l?1; and propionate, up to 111 mg l?1) and pyrite in conjunction with excess inorganic Cl in groundwater are all indicators of ongoing degradation of the chlorinated compounds. However, while natural attenuation of chloromethanes may be a viable adjunct to strategies designed to remediate CT in reducing groundwater, its efficacy is hard to quantify in complex field environments where upgradient sources are still present. |
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