2013 NGWA Summit — The National and International Conference on Groundwater

Field-Scale Application of In-Situ Reductive Dechlorination: Trichloroethene Transformation Mechanism and Rate

Tuesday, April 30, 2013: 1:55 p.m.
Regency West 6 (Hyatt Regency San Antonio)
Xin Song, ARCADIS U.S. Inc.
Denice Nelson, Ph.D., PE, ARCADIS U.S.
Hoa Voscott, ARCADIS U.S.

Trichloroethene (TCE) is one of the most common groundwater contaminants. Although the processes involved in TCE dechlorination are well understood in the fields of chemistry and microbiology, implementation of these processes to large scale plumes during environmental remediation is relatively new. A field investigation on stimulation of anaerobic TCE transformation through introduction of an electron donor was performed at a TCE contaminated site, where fine to coarse sand with discontinuous interbedded silty sand are observed in the aquifer. The objectives of this study are to (1) optimize the large scale field application of enhanced reductive dechlorination, and (2) investigate the in-situtransformation rate of TCE and evaluate TCE transformation pathway.

Specifically, two pilot-scale tests were conducted in-situ to support the full-scale reductive dechlorination system design. In the first pilot-test, an electron donor was introduced via four injection wells to determine the applicability of the selected electron donor (molasses) and optimize the geochemistry conditions (e.g., pH) for enhanced reductive dechlorination via electron donor injection. In the second pilot-test, a tracer (fluorescein) and the selected electron donor were injected into two injection wells to estimate (1) the mobile and immobile porosity values of the aquifer, (2) the transformation rate of TCE, and (3) the ambient groundwater velocity. Following the completion of both pilot-scale tests, the full-scale remediation system was designed and implemented in a layout with four major transects, each of which consists of a number of injection wells in areas with relative high TCE concentrations . In addition, the alternative anaerobic TCE transformation mechanism was evaluated because the traditional sequential reductive dechlorination pathway of TCE—cis-DCE—vinyl chloride —ethene was not observed at the site, and the outcome of which will also be presented.

Xin Song , ARCADIS U.S. Inc.
Xin Song has an M.S. in Environmental Science from Tsinghua University, China. She received her Ph.D. in Civil and Environmental Engineering from the University of Maryland. Song joined Arcadis in 2005 and has been working as a hydrogeologist since then. She has worked on numerous projects on conceptual site model development, numerical flow and solute transport evaluation, and provided technical support on in-situ remediation system design.

Denice Nelson, Ph.D., PE , ARCADIS U.S.
Denice Nelson, Ph.D, P.E. is a Principal Engineer at ARCADIS based in Minneapolis, Minnesota.

Hoa Voscott , ARCADIS U.S.
Mr. Voscott is a certified project manager in ARCADIS.