Technology:
In Situ Thermal Treatment (Electrical Resistive Heating)
- Field demonstration of resistive heating - source zone test plot was 75 ft by 50 ft by 45 ft deep
- 13 electrodes, each consisted of two conductive intervals (25-30 ft bgs and 38-45 ft bgs); lower heating interval configured to provide a “hot floor” for the treated aquifer; total of 1.7 million kW-hrs of energy applied to the subsurface (10 to 400 amps)
- Novel design for the electrodes used for the demonstration - an electrical cable attached to a ground rod within a graphite backfill rather than the traditional pipe electode
- 12 SVE wells installed with 2-ft screens to depth of 4-6 ft bgs; off-gases treated with GAC
- Two major system interruptions during the demonstration - hurricane in September 1999 and replacement of a transformer in March 2000
- Excessive rainfall from the hurricane caused the water table to rise, resulting in insufficient heating of the shallow portion of the test plot; to address the problem, ground rods were installed near the electrodes to heat the 5-10 ft bgs interval
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Cleanup Authority:
Not Provided
Contacts:
Arun Gavaskar
Project Manager
Battelle Memorial Institute
505 King Avenue
Columbus, OH 43201
William Heath
Concurrent Environmental Solutions |
Contaminants:
Halogenated VOCs
- TCE - Estimated mass of 11,313 kg in test plot
- DNAPL - 10,490 kg of the TCE mass was estimated to be DNAPL |
Waste Source:
Wastes from rocket engine and parts cleaning operations |
Type/Quantity of Media Treated:
Soil and Groundwater
- Test plot size - 75 ft by 50 ft by 45 ft |
Purpose/Significance of Application:
Field demonstration of resistive heating using a novel electrode design to treat a DNAPL source area |
Regulatory Requirements/Cleanup Goals:
- The objective of the field demonstration was to reduce the contaminant mass by 90 percent |
Results:
- The mass of TCE and DNAPL in the soil in the test plot was reduced by 90 percent and 97 percent, respectively, exceeding the target of 90 percent mass removal
- Heating was found to be more efficient in the deeper portion of the aquifer, with less heating observed in the shallow portion
- Limitations in the new electrode design and the loss of the vadose zone during the high rainfall event may have contributed to lower heating of the shallow zone
- Sampling hot cores of soil (90°C) may have resulted in some losses of chlorinated VOCs during post- demonstration |
Cost Factors:
- The total cost for the project was $613,000, including $569,000 for resistive heating by the vendor and $44,000 in waste disposal costs paid by NASA
- The $569,000 costs for the resistive heating demonstration included costs for design, equipment, mobilization/demobilization, and operation |
Description:
A 1998 site investigation at the Cape Canaveral Air Force Station in Florida identified a large DNAPL source at Launch Complex 34. Historical activities at the site included discharging wastes generated from rocket engine and parts cleaning operations into discharge pits. Chlorinated solvents, including TCE, were used in these cleaning operations. The Interagency DNAPL Consortium selected this site for demonstrating DNAPL treatment technologies. One of the technologies tested was resistive heating.
A field demonstration of resistive heating was performed from August 18, 1999 to July 12, 2000, with the post-demonstration assessment performed from August to December 2000. The resistive heating system included 13 electrodes with a novel design - an electrical cable attached to a ground rod within a graphite backfill rather than the traditional pipe electode. During system operation, excessive rainfall resulting from a hurricane raised the water table, resulting in the loss of the vadose zone, and insufficient heating of the shallow portion of the aquifer. Ground rods were installed near the electrodes to heat the 5-10 ft bgs interval. Resistive heating reduced the contaminant mass in the test plot by 90 percent for TCE and 97 percent for DNAPL, exceeding the target of 90 percent mass removal. The vendor used a numebr of techniques, including capping the ends of the core sample, to reduce the potential for loss of VOCs during sampling of hot cores. |
