Background/Objectives. Deep fractured rock sites with DNAPL contamination were considered almost impossible to treat just a few years ago, however. Thermal Conductive Heating (TCH) has been proven to be an effective technology to remediate these sites. TerraTherm’s TCH technology was first utilized in 2007 in bedrock to treat a Trichloroethene (TCE) source zone located to a total depth of 90 ft bgs in a saprolite underlain by weathered bedrock and fractured gneiss. Since then, electrical TCH has been utilized to successfully remediate bedrock at more than 10 sites in both the eastern and western portions of the United States and in the northern part of Europe; many of these sites included remediating bedrock DNAPL source zones.
Approach/Activities. In this presentation, lessons learned from more than 10 bedrock remedies will be presented. TCH has been implemented in full-scale applications to treat both saprolite, fractured and more competent granite, gneiss, sand-, silt- and mudstones. The effect of bedrock’s key physical parameters, such as porosity and saturation on heat-up rates and performance, will be discussed. At some sites, the groundwater table has been located deeper than 50 ft bgs, while at others, groundwater was located a few feet from the surface. For all sites and contaminants, a proper extraction strategy for maintaining pneumatic and hydraulic control in the bedrock is key. In addition, the potential for excess groundwater flow in fracture zones must be adequately addressed during design to ensure sufficient heating and treatment. Specific extraction approaches for fracture-dominated settings will be discussed, and examples from sites will be shared where operational data such as temperature profiles have been used to identify high-flowing groundwater zones. Potential mitigation measures to address the cooling effects of high groundwater flux zones will also be discussed. TCH has been implemented at bedrock sites as deep as 170 ft bgs and strategies and approaches for proper well installation in deep bedrock settings will also be discussed.
Results/Lessons Learned. The basics for utilizing TCH to treat fractured bedrock and dual porosity systems will be presented, backed up by real-life examples from completed sites. The focus of the presentation will be on describing the heating approach as well as factors determining the efficiency of the thermal remedy. Also, well installation strategies and how to properly utilize information gained in the installation process to optimize the thermal remedy will be presented, along with examples from sites where heating was impacted by location hydrogeology and fracture systems. Documenting and verifying remedial performance at bedrock sites can be challenging. Approaches utilizing both vapor concentrations, groundwater concentrations, and rock concentrations or combinations thereof will be discussed along with monitoring data showing continued decreasing concentration trends several years after the thermal remedy was completed.