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A borehole test for chlorinated solvent diffusion and degradation rates in sedimentary rock

January 13, 2022

We present a new field measurement and numerical interpretation method (combined termed ‘test’) to parameterize the diffusion of trichloroethene (TCE) and its biodegradation products (DPs) from the matrix of sedimentary rock. The method uses a dual-packer system to interrogate a low-permeability section of the rock matrix adjacent to a previously contaminated borehole and uses the borehole monitoring history to establish the pre-test condition. TCE and its DPs are removed from the groundwater between the packers at the onset of the testing. The parameters estimated by fitting a radial diffusion model to the concentration history and borehole concentration data, also termed back-diffusion, are the tortuosity factor and sorption coefficients of TCE and DPs in the rock matrix and the TCE and DP biodegradation rate coefficients in the borehole. We demonstrate the equipment design and the interpretive method using a borehole accessing the grey mudstone at a TCE contaminated site in the Newark Basin. In this test, both nonreactive (bromide) and reactive (trichlorofluoroethene) tracers are used to constrain the estimated parameters; however, the bromide tracer was not needed to estimate the parameters in this test. The parameters estimated from the field test are consistent with values measured independently in laboratory experiments using field samples of similar lithology. From the interpretation, we compute the TCE and DP concentration distributions in the rock matrix prior to the test to illustrate how the results can be used to enhance understanding of contaminant distribution in the rock matrix.

Publication Year 2022
Title A borehole test for chlorinated solvent diffusion and degradation rates in sedimentary rock
DOI 10.1111/gwmr.12495
Authors Richelle M. Allen-King, Rebecca L. Kiekhaefer, Daniel J. Goode, Paul A. Hsieh, Michelle Lorah, Thomas E. Imbrigiotta
Publication Type Article
Publication Subtype Journal Article
Series Title Groundwater Monitoring and Remediation
Index ID 70227624
Record Source USGS Publications Warehouse
USGS Organization Maryland Water Science Center; New Jersey Water Science Center; Pennsylvania Water Science Center