The purpose of this project was to demonstrate the utility of flux-based methods for assessing long-term post-remedial performance of groundwater treatment technologies. Specific objectives of this project were to: 

  1. Estimate period of record and post-remedial contaminant mass balance through the use of measured fluxes and calculated contaminant discharges while incorporating estimates of the associated flux and discharge uncertainties. 
  2. 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. 
  3. Demonstrate the baffled multi-level sampler (BMLS) as a tool allowing for cost effective long-term flux-based monitoring.

Technology Description

For this project, local contaminant mass flux and integrated mass discharge in groundwater were measured using BMLS and passive flux meters (PFMs). Both methods collected data to determine the 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. BMLS have been utilized successfully for multiple projects in cooperation with the United States Department of Energy, Lawrence Berkley National Laboratory, and now this project.

APL Area 1 Comparison of Historical Pre-remediation (2003) and Post Remediation (2006) TCE Mass Flux Distribution

Demonstration Results

The intent of this project was to provide a more cost-efficient method for long-term flux-based monitoring of contaminated groundwater sites. The cost analysis compares the cost of a one-year effort to collect monthly flux data for two scenarios. For the first scenario, total cost is based upon all monthly measurements being collected using PFMs, while the total cost of the second scenario is based upon one initial PFM and BMLS baseline deployment, with all subsequent monthly measurements being performed with BMLS. The results demonstrate that over a one-year sampling campaign, Scenario 2 provides a savings of $368,742. For longer sampling campaigns, the savings with Scenario 2 would continue to increase. The outcome is a reliable flux-based long-term groundwater monitoring strategy using both PFMs and BMLS while providing significant savings over a method using just PFMs.

Implementation Issues

The BMLS and PFM technologies currently function through deployment of custom-built devices designed with specified interrogation zones based upon site conditions. Field implementation is straightforward and staff from the United States Environmental Protection Agency, United States Geological Survey, United States Department of Energy, and United States Army Corp of Engineers have been successfully trained with minimal issues in methodology transfer. (Project Completion - 2022)