The objective of this project is to demonstrate the utility of flux-based methods for assessing long-term post-remedial performance. Specific objectives are to:
- Estimate period of record (2003-present) and post-remedial (2006-2016) contaminant mass balance through the use of measured fluxes and calculated contaminant discharges while incorporating estimates of the associated flux and discharge uncertainties.
- Evaluate overall performance of thermal remediation to date using contaminant discharge history (and inferred reduction of contaminant mass) as the primary metric, while accounting for flux and discharge uncertainty.
To demonstrate the utility of flux-based methods for assessment of long-term post-remedial performance, data collected at Fort Lewis Army Base (now Joint Base Lewis-McChord) will be used. Fort Lewis offers a unique opportunity because it is a large dense nonaqueous phase liquid (DNAPL) contaminated site with extensive characterization data and a major source-zone remedial effort that included collection of flux data as a component of the remedial performance assessment (SERDP project ER-1295). One outcome of the previous effort was a preliminary assessment of post-remedial performance at the Fort Lewis East Gate Disposal Yard (EGDY) site through 2010. Building on this previous work, the project team (University of Florida and U.S. Environmental Protection Agency) will perform a follow-up effort to evaluate long-term remedial performance using a flux-based mass balance approach that incorporates estimates for flux and mass discharge uncertainties. For this project, local contaminant mass flux and integrated mass discharge will be measured using passive flux meters (PFM) and baffled multi-level samplers (BMLS). Both methods collect data that can be used to estimate local mass flux [mass per unit area per time] that can be spatially integrated to determine mass discharge [mass per time]. The PFM was initially developed at the University of Florida under ESTCP project ER-200114 (US Patent 6401547). The BMLS is a convenient tool for relating observed water levels and measured aqueous contaminant concentrations to water and contaminant fluxes measured with PFM.
The resulting analyses and methods will provide a tool not only for evaluating long-term post-remedial performance that accounts for discharge uncertainty at this site, but also for evaluating remedial design, site management, and post-remedial performance at other Department of Defense installations. The introduction of aqueous concentration data collected with BMLS and calibrated to PFM-measured flux averaged concentrations will allow for future flux and discharge estimates based solely on BMLS aqueous samples and water level measurements, allowing for continued tracking of long-term post-remedial performance with minimal effort and cost. (Anticipated Project Completion - 2018)