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

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.