Chemical treatment of petroleum-contaminated soil in cold regions is generally regulated as an ex situ process. Contaminated soil is excavated and constructed as a lined heap, or is stockpiled for parceling in a liquid/solid contactor. In heaps, oxidative degradation of contaminants occurs with infusion of peroxide (O22-), hydrogen peroxide (H2O2), and/or ozone (O3). In a contactor, petroleum is liberated by electro-oxidation with use of an oxidizing agent that has a high redox potential, or from soil that is submerged in an alkaline solution amended with a surfactant. In such applications, efficiency of petroleum reduction is a function of slurry temperature and oxidizing agent/surfactant concentration (Riser-Roberts 1998). Although chemical treatment of petroleum-contaminated soil is slow, removal efficiencies can exceed 90% with sands and gravels (Suthersan 1997). A disadvantage of chemical treatment of petroleum-contaminated soil is that residual waste may require additional handling as a hazardous material.
In situ soil washing is not recommended for use at petroleum-contaminated sites in polar regions where subsurface controls on migration are not in place. Furthermore, this method is cost-prohibitive (Antarctica) or may be tightly restricted for arctic use (Canada, United States, and Norway). However, although seldom used, ex situ soil washing is a useful method for petroleum-contaminated sites in cold regions. Ex situ soil washing is a chemical treatment method that is performed in a reactor. Modern reactors are two-stage (hot-water surfactant washing and flotation processes) or three-stage (with addition of biological treatment of leachate). An advantage of compartmentalized reactors is that each stage can be optimized independently. However, treatment efficiency is highly dependent on surfactant concentration; concentrations exceeding 2% can reduce slurry hydraulic conductivity and significantly increase the amount of residual waste (Riser-Roberts 1998). Mobile reactors are available for remote use, mixing could be added to the initial washing stage to accommodate peaty and some clayey soils, and a diesel-electric generator or solar collection system (Livingstone 2007) could power physical and chemical processes through the May to September arctic operating season. Furthermore, petroleum-contaminated water from the site could be used as the base washing liquid.
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