Background/Objectives. Remediation of bedrock sites is gaining more and more traction, as the development in remediation technologies allows bedrock contamination to be targeted, that just a few years ago would have been considered technically infeasible to clean-up. One in-situ technology that has repeatedly shown to be very effective in meeting remedial goals in bedrock is Thermal Conduction Heating (TCH). TCH has been shown to address DNAPL even in competent bedrock on several sites in recent years. At many sites, where bedrock is not located to surface, the majority of contamination is located in the overburden above the bedrock surface; however, in many cases the bedrock/overburden interface is found to be home for DNAPL source zones. Coupling that with an ever-changing bedrock surface, that can undulate substantially across a source zone, it is clear that an adaptive approach is needed when installing in-situ remediation system to target bedrock contaminations.    

Approach/Activities. Utilizing TCH, the remediation boring pattern can be flexible, and heater boring depths can be adjusted on a well by well basis as needed, as opposed to some of the other thermal technologies widely used. Therefore, the technology allows for a flexible system installation. Coupled with TCH well spacings of approximately 14-17 ft, well installation reveals details of local contaminant distribution and geology, otherwise not typically delineated at the same resolution prior to well installation. When drilling on TCH bedrock sites, bedrock is tagged and contaminant results are evaluated in near real time. The data is used to adjust the design on-the-fly and to make sure to extend the heated treatment zone down below the DNAPL source zone to prevent downward mobilization. The DNAPL source zones have changed dramatically as a result of the collected data. This adaptive design approach has been utilized on several bedrock/overburden sites, to surgically target a source zone that otherwise would only have been partly remediated.

Results/Lessons Learned.  In this presentation, three sites will be presented where an adaptive design approach has been utilized to surgically treat to the bedrock/overburden interface, based on information gained during well installation. Both small and big sites are presented, with treatment volumes ranging from 5,000 to 57,000 cy, and contaminations ranging from MGP waste over solvent mixes to regular CVOC contamination. Bedrock variations ranged from just a few feet across one of the sites to up to 25 ft feet between two borings installed just 15 ft apart at another site. The great variation posed some design challenges that were addressed during the well installation. This presentation will present the adaptive installation and design adjustment approach, key thermal operational data and results showing that the remedial goals were met on all three sites, even at the undulating bedrock/overburden interface.