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LOCALIZED RECHARGE INFLUENCES ON MTBE TRANSPORT AND WELL PLACEMENT CONSIDERATIONS
Citation:
Weaver, J W. LOCALIZED RECHARGE INFLUENCES ON MTBE TRANSPORT AND WELL PLACEMENT CONSIDERATIONS. Presented at 17th Annual International Conference on Contaminated Soils, Sediments and Water, Amherst, MA, October 21-25, 2001.
Impact/Purpose:
Provide distribution of a suite of peer-reviewed, tested and supported models to customers via the internet, free of charge. Provide training opportunities via the environmental education program for learning about environmental protection, modeling, modeling applications, and the models distributed by CEAM. When appropriate and requested, CEAM personnel provide site-specific application support.
Description:
Vertical characterization of a gasoline release site at East Patchogue, New York showed that methyl tert-butyl ether (MTBE) and aromatic plumes "dived" as they passed beneath a sand pit. That this behavior was caused by aquifer recharge was shown by two pieces of evidence. First by conducting a detailed investigation of hydraulic conductivity variation in wells on either side of the sand pit it was shown that no preferentially flow paths exist. Second, by modeling flow in the aquifer, the pattern of recharge in the aquifer was shown to be sufficient to cause the observed vertical migration of the plumes. The model, available as an calculator on the EPA web site (http://www.epa.gov/athens/onsite), is based on an analytical solution of the flow equation and the theory of three-dimensional streamlines in Dupuit flow. As further confirmation the model has been shown to reproduce observed plume diving patterns at similar sites on Long Island. These sites provide confirmation of the concepts and the ability to develop models to reproduce field behavior. From this work cost-effective approaches for site characterization could be developed that include model forecasts of plume diving to determine well screen placement. For design of sampling networks additional capabilities must be included in the model, because of unusual features of the Long Island sites: established, well-characterized plumes and unique hydrogeologic characteristics. For sites without existing data there is a need to expand the model to include contaminant transport. By using the estimated release date and transport time to the recharge zones it can be determined if a plume is likely to be affected by the feature. This capability has been added to the calculator and compared against data from the East Patchogue site. Further work is underway on building more flexibility in the flow model.