Use low temperature RFH to accelerate in situ degradation of pure solvent via reduction in thermal half-life from years to days at a target temperature of 50o to 60oC — abatement of the solvent source area in fractured bedrock to cause plume regression and enable monitored natural attenuation of residual impact.
Application of this new thermal treatment method beneath an active facility required careful planning and execution to meet project objectives and ensure safety of workers and building occupants- achieved through phased, systematic application and monitoring to document adherence to safety requirements at each level prior to proceeding to the next phase. Antenna design and modular deployment of a four antenna square array in lifts enabled the flexibility necessary to heat over an 80 foot thickness of saturated gneissic bedrock to depths of 100 feet to achieve the volumetric coverage of 11,000 cyds (8,000 cubic meters) to the target temperature of 50 to 60 C. The treatment system includes a network of nine, 30.5-meter deep, 20-cm diameter boreholes, an RF generator, a four-probe transmitter array, and a soil vapor extraction (SVE) system for control and treatment of vapors.
The RF heating system employed at the site consists of a 27 Megahertz (MHz) four channel, 20-kilowatt (kW) RF equipment trailer, transmission lines, four water-tight antennae, applicators, and fiber optic thermometry. The antennae are placed in the boreholes and are spaced approximately 4.5 meters apart in a square array. Each antenna was typically 3 meters long and 6.5 centimeters in diameter and received a maximum of 5 kW from the RF generator module. The antennae were placed in eight boreholes at a depth of 30.5 meters in deep open bedrock and produced a vertical and a horizontal electrical field distribution of 4.6 meters. The electrical field generated from the RF heating system simultaneously targeted 860 cubic meters of fractured bedrock. The RF heating system was operated for 36 months at a maximum output of 19 kW.
Pre and Post Treatment Contours of Radiofrequency Fractured Bedrock Heating Results (Significant TCA Reductions within contours) near I-91 near Boston after 36 months.