From the 1920's until 1980, Southern California Edison (SCE) treated wood power poles with creosote and pentachlorophenal wood preservatives to lengthen their useful lives by decades. During this time, some of the preservatives leaked into the ground. At SCE's former pole treating facility in Visalia, a total of 160,000 gallons of wood preservatives leaked out and penetrated roughly 100 feet into the ground water beneath the site.
In 1989, the former Visalia plant was added to the list of sites to be cleaned up under the federal Superfund law passed in 1980. Initially, a "pump-and-treat" strategy was approved and used at Visalia as the best way to remove the contaminants. The process pumped the contaminated ground water through a treatment system, then returned the clean water back to the environment. While effective, the "pump-and-treat" process did not assure the Visalia site would ever be returned to productive use.
Joining forces with the Lawrence Livermore National Laboratory and the University of California at Berkeley, SCE implemented an emerging technology called Dynamic Underground Stripping (DUS) that has greatly accelerated the rate of contaminant removal at the Visalia site.
This technology uses steam injection and vacuum extraction in soil and groundwater to remove the wood preservative chemicals. Edison also used an innovative thermal imaging technology called Electrical Resistance Tomography (ERT) to monitor and control the subsurface soil and groundwater temperatures in order to maximize the extraction of contaminants.
