Groundwater Modeling and Monitoring Results for a Combined Thermal and In-Situ Bioremediation Remedy

MODFLOW and MT3DMS models originally developed for contaminant fate and transport for the site and proximal portion of the downgradient plume area were converted into a heat transport model to evaluate the evolution of groundwater temperature over time and distance from the thermal treatment area. We present modeled temperatures and field data for downgradient temperatures associated with a source area thermal remedy, and the influence of the thermal front on a combined anaerobic bioremediation / chemical reduction remedy implemented in the proximal portion of the downgradient plume. The objective was to take advantage of the increased microbial activity and CVOC desorption to enhance bioremediation of the chlorinated plume immediately downgradient of the source area. Permeable reactive barrier zones comprised of a mixture of zero-valent iron and organic carbon substrate were installed to take advantage of the anticipated higher groundwater temperatures and provide abiotic degradation in the event of temperature excursions beyond those at which subsurface biological activity shuts down. The system was installed in December of 2017 and run for approximately 180 days. Adjustments to the thermal model to account for winter conditions and the use of a quench line to protect nearby utilities will be discussed. Groundwater temperature and chemistry data available from post shutdown monitoring will be discussed and presented to evaluate modeling efforts and system effectiveness.