U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
Desorption of Trichloroethylene From Aquifer Sediments at Picatinny
Arsenal, New Jersey
by
David Koller (U.S. Geological Survey, 810 Bear Tavern Road, Suite
206, West Trenton, NJ 08628), Thomas E. Imbrigiotta (U.S. Geological Survey,
810 Bear Tavern Road, Suite 206, West Trenton, NJ 08628), Arthur L. Baehr
(U.S. Geological Survey, 810 Bear Tavern Road, Suite 206, West Trenton,
NJ 08628), and James A. Smith (Department of Civil Engineering and Applied
Mechanics, University of Virginia, Charlottesville, VA 22903-2442)
Abstract
Desorption of trichloroethylene (TCE) from contaminated aquifer sediments
is postulated to be a continuing source of this contaminant to ground water
downgradient from the site of a former metal-plating/degreasing operation
at Picatinny Arsenal in north-central New Jersey. Flow-through columns were
constructed using sediments from four sites within the TCE plume to determine
whether TCE desorption was occurring and, if so, at what rate. Results of
the column experiments with contaminated sediments indicate that TCE desorption
is occurring at all sites tested. Desorption in these columns appeared to
occur in two stages--an initial, rapid stage (days to weeks) during which
1 to 10 percent of the total sorbed mass of TCE is released, followed by
a slow stage (months to years) during which the remaining 90 to 99 percent
is desorbed. Results of a column experiment using sediment artificially
contaminated in the laboratory for only 5 days showed the same two-stage
desorption, but 65 to 70 percent of the sorbed TCE was desorbed in the initial,
rapid stage, and the remaining 30 to 35 percent was desorbed in the slow
stage.
A one-dimensional model was developed to determine the desorption
rates by simulating the desorption measurements from
the column experiments. The model simulates the initial, rapid-stage
desorption as an equilibrium process, and simulates
the second, slower stage desorption as a kinetic process. Results
of model simulations compared well with results of the column
experiments. Long-term (slow-stage) rate constants for
TCE desorption from Picatinny Arsenal soils calculated by using
the model ranged from 0.5 x 10-8 to 2.5 x 10-8
per second.
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