Investigation and Remediation of a 1,2–Dichloroethane Spill Part I: Short and Long-Term Remediation Strategies |
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| Authors: | Lily Sehayek Terry D. Vandell Brent E. Sleep Michael D. Lee Calvin Chien |
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| Affiliation: | 1. Lily Sehayek (Penn State Great Valley, Engineering Division, Graduate Center of the Pennsylvania State University, 30 East Swedesford Rd., Malvern, PA 19355) received a Ph.D. in civil and environmental engineering from Rutgers University. She has more than 15 years experience in government, consulting, and industry, and three years experience in academia. Her research includes multiphase flow and transport modeling, simulation of in situ bioremediation, and watershed management and modeling.;2. Terry D. Vandell is a senior environmental consultant at Conoco (1000 S. Pine, Ponca City, OK 74602). She is a project director working on the investigation and remediation of several DNAPL sites in the Gulf Coast region. She received an M.S. in hydrogeology from the University of Idaho and has worked in ground water investigation and remediation for more than 20 years.;3. Brent E. Sleep (University of Toronto, Department of Civil Engineering, 35 Saint George St., Toronto, Canada M5S1A4) received a B.S. and an MS. in chemical engineering and a Ph.D. in civil engineering from the University of Waterloo. He is an associate professor in the Department of Civil Engineering at the University of Toronto. Current research activities include modeling and laboratory and pilot scale studies of LNAPL and DNAPL remediation techniques.;4. Michael D. Lee is vice president of Terra Systems Inc. (1035 Philadelphia Pike, Ste. E, Wilmington, DE 19809). He received a B.S. in biology from Northeast Louisiana University and an M.S. 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.;5. Calvin C. Chien is a senior environmental fellow with DuPont Co. (DuPont Corporate Remediation, Barley Mill Plaza 27/2228, Routes 141 and 48, Wilmington, DE 19805). He received Ph.D. from the State University of New York at Buffalo in hydrologic system modeling. He is a remediation technology team leader with the company and a member of EPA's Science Advisory Board, serving on the Environmental Engineering Committee and Environmental Modeling Subcommittee. |
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| Abstract: | Release of an estimated 150,000 gallons (568,000 L).of 1.2–dichloroethane (EDC) from a buried pipeline into a ditch and surrounding soil resulted in shallow subsurface contamination of a Gulf Coast site. Short-term remediation included removal of EDC DNAPI. (dense nonaqueous phase liquid) by dredging and vacuuming the ditch, and by dredging the river where the ditch discharged. EDC saturation in shallow impacted sediments located beneath the ditch was at or below residual saturation and these sediments were therefore left in place. The ditch was lined, backfilled, and capped. Long-term remediation includes EDC DNAPL recovery and hydraulic containment from the shallow zone with long-term monitoring of the shallow, intermediate, and deep (200 foot) aquifers. Ground water, DNAPL., and dissolved phase models were used to guide field investigations and the selection of an effective remedial action strategy. The DNAPL. modeling was conducted for a two-dimensional vertical cross section of the site, and included the three aquifers separated by two aquitards with microfractures. These aquitards were modeled using a dual porosity approach. Matrix and fracture properties of the aquitards used for DNAPL modeling were determined from small-scale laboratory properties. These properties were consistent with effective hydraulic conductivity determined from ground water flow modeling. A sensitivity analysis demonstrated that the vertical migration of EDC was attenuated by dissolution of EDC into the matrix of the upper aquitard. When the organic/water entry pressure of the aquitard matrix, or the solubility of EDC were decreased to unrealislically low values. EDC DNAPL. accumulated in the aquifer below the upper aquitard.
EDC DNALM, did not reach the regional (deepest) aquifer in any of the cases modeled. The limited extent of vertical EDC migration predicted is supported by ground water monitoring conducted over the four years since the spill. |
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