Trichloroethylene (TCE) Sorption to Organic Matter in Sedimentary Rocks of the Newark Basin
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The former Naval Air Warfare Center (NAWC), located in Trenton New Jersey, is contaminated with trichloroethylene (TCE) despite more than 20 years of pump and treat remediation. NAWC sits atop formations of the Newark Basin, which is comprised of a variety of fractured, low permeability mudstones ranging in over an order of magnitude of fraction of organic content (foc) (0.13%-3.3%). These mudstones have been thermally altered relatively uniformly, resulting in similar degrees of organic maturity. Batch sorption experiments were conducted to generate TCE isotherms spanning five orders of magnitude in aqueous concentration. The samples used in the experiments represent the major repeating lithologies present at NAWC. The isotherms revealed nonlinear Freundlich slopes ranging from 0.51 to 0.57. These slopes show that pore-filling is a favored sorption mechanism. The similarity of the slopes suggests that the organic matter in each sample has a similar degree of thermal maturity. The foc normalized isotherms were compared to TCE isotherms for organic matter in different stages of maturation. The NAWC isotherms were most similar to the isotherms for charcoal and high volatile bituminous coal. This suggests that the organic matter has similar pore volume structure and maturation. The foc, normalized isotherms showed a range of sorption capacity (Kf), with the high foc samples almost an order of magnitude higher than the low foc samples. I posit that the range could indicate different sources of organic matter. The organic matter in high foc samples is mostly algae and bacteria, while the low foc samples are comprised of mostly woody land plant matter. I estimated high retardation factors at low aqueous concentrations for the NAWC lithologies. At 100 ug/L, the range of retardation factors was approximately 150 to 15,000. These high retardation factors, coupled with the high TCE sorbed mass storage capacities, indicate that TCE sorbed in the matrix will serve as a secondary source to groundwater in the fractures, extending the time necessary for remediation and plume retreat.