Conceptual Model - Solvent Plume
Conceptual Model – Solvent Plume
The property owner was selling the facility but retaining environmental liability. Several earlier investigations had not adequately answered the questions of off-site contaminant migration and risk posed by historical releases of solvents to the subsurface.
The challenge included determining how much money would be needed in escrow, and how much liability should be claimed in corporate financial projections to meet the requirements of the Sarbanes-Oxley Act.
JCO reviewed approximately six years of existing data from previous investigations to develop a conceptual model for this chlorinated solvent-contaminated site. The conceptual model relied on the following contaminant fate and transport theory:
Dissolved chlorinated solvent contamination in the unconsolidated deposits continues to migrate, and the fractured bedrock contamination has reached a stable steady-state condition downgradient from dispersed DNAPL sources.
JCO performed site characterization and monitoring to substantiate the contaminant fate and transport theories, and to determine if unacceptable risks to receptors are present. These activities included:
- seasonal sampling of monitoring wells in unconsolidated deposits and bedrock, including analysis of inorganic parameters related to biodegradation potential, and volatile organic parameters to assess plume stability and migration potential
- extensive and continuous water-level monitoring during bedrock aquifer pumping
- semi-annual indoor air monitoring, and
- rapid adaptive drive point groundwater profiling coupled with on-site analysis of samples with gas chromatography to delineate the dissolved chlorinated solvent plume in unconsolidated deposits.
We were able to demonstrate that:
- the dissolved chlorinated solvent plume in the unconsolidated deposits could be easily intercepted and treated to eliminate off-site migration
- monitored natural attenuation is an appropriate remedy for the source area and bedrock aquifer that sufficiently manages risks to building occupants and downgradient receptors
- the dissolved chlorinated solvent plume in bedrock remains at a steady-state condition with no interferences in flow from upgradient bedrock pumping, and
- no unacceptable risks are present as a result of the contamination.
The property owner was able to estimate its future financial liabilities and not embark on a very expensive remedial action.