Inverse Analytical Techniques Applied to Coincident Contaminant Distributions at Otis Air Force Base, Massachusetts

Authors


  • Discussion open until September 1, 1992.

  • Natalyn K. Ala graduated from Texas A & M University with a B.S. in Engineering Geology and an M.S. in Hydrogeology. Currently she is a Hydrogeologist for URS Consultants Inc. in Long Beach, California where her work mainly has involved characterization and modeling of ground-water flow. Her other tasks include studying and modeling the transport of contaminants in the subsurface.

  • P A. Domenico is currently Harris Professor of Geology at Texas A & M University. He was formerly Professor of Geology at the University of Illinois at Urbana-Champaign during the period 1968 to 1982. Previous to that time he was a Research Associate Professor at the Desert Research Institute, University of Nevada at Reno.

Abstract

Inverse analytical techniques have been applied to six coincident plumes at Otis Air Force Base near Cape Cod, Massachusetts. The plumes contain chloride, boron, trichloroethene, tetrachloroethene, and biodegradable and nonbiodegradable detergents. Thus, a host of processes including physical, chemical, and biological, are presumed to be operative. The analytical technique is structured to solve several equations simultaneously and provides unique values for several unknowns which control the behavior of the contaminant plumes. The determined parameters include source strength and size, the advective position of the contaminant front for both retarded and unretarded constituents, dispersivities in x and y, and a reaction rate constant that describes decay, biodégradation, or chemical transformation. The obtained values for the transport parameters for the different constituents were reasonably similar, with the transverse dispersivity ranging from 1.2 to 2.7 m and the longitudinal dispersivity ranging from 6.1 to 7 m. The unretarded advective velocity of boron, chloride, and tetrachloroethene were quite similar (73, 78, and 65 m/yr) whereas tetrachloroethene had a velocity of 48 m/yr. Of special interest is the half-life determination of the reactive constituents. The organic compounds trichloroethene and tetrachloroethene have half-lives of 11 and 10 years, respectively, whereas the biodegradable detergent with linear alkyl sulfonate had a half-life of 7.6 years. In all cases, this set of parameters captures the essence of the various plumes with a high degree of accuracy.

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