Superfund Innovative Technology Evaluation (SITE)
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Situ Electrokinetic Extraction System
Sandia National Laboratories (SNL) has developed an in situ soil remediation system that uses electrokinetic principles to remediate hexavalent chromium-contaminated unsaturated or partially saturated soils. The technology involves the in situ application of direct current to the soil, which results in dissolved chromate ions migrating through water in soil pores to the oppositely charged electrode, a phenomenon known as electromigration. Chromate ions are extracted in the anode effluent. The In Situ Electrokinetic Extraction (ISEE) technology was demonstrated at SNL's Unlined Chromic Acid Pit (UCAP) from May 15 to November 24, 1996. The target contaminant was hexavalent chromium in the form of chromate ions.
The ISEE technology developed by SNL is applicable for treating unsaturated soil contaminated with chromate ions. According to SNL, this technology can be modified to treat saturated contaminated soils and to remove contaminants besides chromate dissolved in the pore water.
During the SITE demonstration, 13 tests were performed during six phases. The test areas ranged from 36 to 72 square feet over a zone of contaminated soil from 8 to 14 feet below ground surface.
At the system's preferred operating conditions determined by SNL (test 13), (1) approximately 200 grams (g) of hexavalent chromium were removed during about 700 hours of operation (0.29 g per hour), and (2) the overall removal efficiency for the system was approximately 0.13 g of hexavalent chromium per kilowatt hour.
Within the test areas, 18 out of 43 pre-demonstration soil samples exceeded the TCLP limit of 5 milligrams per liter (mg/L) of total chromium.