Soil vapor extraction, electrical heating

A network of 107 electrodes covering two-thirds of an acre was established. To treat beneath a warehouse, 85 of those electrodes were constructed directly through the floor of the building. Electrically conductive from 11-21 ft bg, the electrodes actively heated the depth interval from 5-24 ft bg. Once subsurface temperatures reach boiling, steam laden wifli chlorinated solvents was collected by a network of 37 soil vapor extraction wells screened to 5 ft bg. 

Recalcitrant organic contaminants in the unsaturated zone, those that are difficult to remediate by vapor extraction, biodegradation, or other biological-chemical processes, can be removed via vitrification and electrical heating. This process involves heating the soil by electrical resistance or applied electrical fields to vaporize semi-volatile and volatile compounds, thermally to break down larger organic molecules, and (if heated sufficiently) to vitrify the mineral matter in the soil. 

A 4-month vapor extraction project in which the soil was heated to 160°F would require approximately 200,000 Bm/yd. According to the vendor, the energy cost for electricity-provided heat would be about 6.00/yd. For natural gas and propane, the cost would be lowered to 1.00 and 1.60/yd, respectively (D15838X, p. 2). 

---