Controlled vadose zone saturation and remediation (CVSR) is essentially a long overdue advancement of standard in situ treatment methods that have been traditionally used in the saturated zone. Unsaturated zone treatment technologies are not new, but they normally revolve around mechanical operations such as soil vapor extraction (SVE). While the cost of CVSR is comparable to SVE, it can generally be performed within a much shorter timeframe (6 months). To our knowledge, this is only the second published report combining CVSR with in situ chemical oxidation (ISCO). CVSR technology was successfully applied to an active industrial site in Illinois. Alkaline activated sodium persulfate using sodium hydroxide was used to treat the shallow soils to a depth of 15 feet. The vadose zone soils were contaminated with a variety of VOC constituents including PCE, TCE, methylene chloride, ethylbenzene, toluene, and total xylenes. Prior to the field injections, a soil buffering test was performed in the laboratory in order to determine the amount of sodium hydroxide needed to raise the pH of the soil to above 10.5 units and maintain it for five days. Because chemical oxidation relies on diffusion of oxidants in an aqueous medium, the vadose zone soils were saturated using a combination of vertical injection wells, an infiltration gallery, and horizontal injection wells installed beneath two small buildings. The infiltration gallery and the horizontal wells were initially used to percolate water into the vadose zone to achieve saturation. The vertical and horizontal wells were then used to inject the hydroxide and oxidant. A total of 12 vertical injection wells where installed in two treatment areas along with the infiltration gallery. Due to the presence of low permeability silts and clays, each vertical injection well had an estimated radius of influence of 10 feet. Approximately 4,700 gallons of sodium hydroxide (25% concentration) and 11,500 pounds of sodium persulfate were injected over a 27 day period in November and December of 2008. A second injection of activated persulfate was performed in Area 1 in August 2009. The concentrations of the compounds of concern, PCE, TCE, methylene chloride, ethylbenzene, toluene, and total xylenes, all decreased from 88% to 99% within 180 days after treatment. The ISCO injections attained the site-specific soil cleanup criteria, in conjunction with an engineered barrier, established by the State of Illinois EPA.
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