Investigation and Remediation of a 1,2-Dichloroethane Spill Part II: Documentation of Natural Attenuation |
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| Authors: | Michael D. Lee Lily Sehayek Brent E. Sleep Terry D. Vandell |
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| Affiliation: | Michael D. Lee is vice president of Terra Systems Inc. (1035 Philadelphia Pike, Ste. E, Wilmington, DE 19809;(3021798-9553;fax: [.302] 798-9554;e-mail: ). He received a B.S. in biology from Northeast Louisiana University and an MS. and Ph.D in environmental science and engineering from Rice University. His research interests are in the intrinsic and enhanced biodegradation of chlorinated solvents in soil and ground water.;Lily Sehayek (Pennsylvania State University Great Valley, Graduate Center o f the Pennsylvania State University, 30 East Swedesford Rd., Malvern, PA 19355) received a B.S. in chemistry and an M.S. in waste water treatment from Cape Town University, South Africa, and a Ph.D. in civil and environmental engineering from Rutgers University. Her research interests are ground water flow and transport modeling, and application of artificial intelligence in the environmental field.;Brent E. Sleep (University of Toronto, Department of Civil Engineering, 35 Saint George St., Toronto, Canada M5S1A4) received a B.A.Sc. and an M.A.Sc. from the University of Waterloo in chemical engineering, and his Ph.D. from the University of Waterloo in civil engineering. He is an associate professor in the Department of Civil Engineering at the University of Toronto. His current research activities include computer modeling, and laboratory and pilot scale studies of LNAPL and DNAPL remediation techniques.;Terry D. Vandell is a senior environmental consultant at Conoco (1000 S. Pine, Ponca City, OK 74602). Ms. Vandell is a project director, working on the investigation and remediation of this and several other DNAPL sites in the Gulf Coast region. She received an MS. in hydrogeology from the University of Idaho, and has worked in ground water investigation and remediation for more than 20 years. |
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| Abstract: | A release of 1,2-dichloroethane. also known as ethylene dichloride (EDC), resulted in shallow subsurface freephase contamination of a Gulf Coast site in the southern United States. The site stratigraphy consists primarily of a low permeability, surficial peat. silt, and clay zone underlain by fractured clay; a confined 12 in deep sand ground water flow zone; a confined 21 m deep fine sand zone of limited ground water flow, followed by a deep aquitard. The Gumbo clay and sandy clay aquitard below the release area overlies and protects the 61 m deep Upper Chicot Aquifer, which is a confined regional aquifer. An ongoing recovery and hydraulic containment program from the primary impacted and laterally and vertically restricted shallow 40-foot sand zone has effectively recovered dense nonaqueous phase liquid (DNAPL) and contained dissolved phase EDC.
Natural attenuation of EDC was demonstrated through (1) a laboratory microcosm study substantiating the ability of the native microbial population in the deeper aquifer lo degrade EDC under anaerobic environmental conditions found at the site. (2) field investigations showing reductions in EDC concentrations over time in many of the wells on site, and (3) an evaluation of the ground water for EDC and its degradation products and oilier geo-chemical parameters such as dissolved oxygen, redox potential, and pH. Degradation products of EDC found in the field investigations included 2-chloroeihanol, ethanol. ethene, and ethane. Dissolved EDC concentrations in selected wells between the first recorded samples and the fourth quarter of 1997 ranged from greater than 4% to 99% reductions. First-order exponential decay half-lives ranged from 0.21 to 4.2 years for wells showing decreases in FDC concentrations over time. Elevated methane concentrations indicated carbon dioxide to be the major terminal electron acceptor. |
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