Contaminated Soil

The cleanup of contaminated soil can involve significant expense and environmental risk. In general, containment is cheaper and has fewer environmental consequences than soil treatment. The Superfund law establishes a preference for these supposedly permanents remedies, but many Superfund cleanups have occurred at sites that used both containment and treatment options. In cases where containment measures failed, or were never instituted, in situ treatment methods, such as groundwater pump-and-treat, are generally preferable to extractive approaches like soil incineration because they are often less expensive. Excavation and incineration of contaminated soil can cost $1,500 per ton, leading to total costs of many millions of dollars at large sites. (Superfund clean-ups have averaged about $26 million.) In contrast, small fuel spills at gasoline stations may be mitigated using vapor extraction at costs under $50,000. However, in situ options may not achieve cleanup goals.

Unlike air and water, which have specific federal laws and regulations detailing maximum allowable levels of contaminants, no levels have been set for contaminants in soil. Instead, the federal Environmental Protection Agency and state environmental agencies use subjective, case-specific criteria to set acceptable contaminant levels. For Superfund sites, cleanup standards must exceed applicable or relevant and appropriate requirements (ARARs) under federal environmental and public health laws. Cleanup standards are often determined by measuring background levels of the offending contaminant in similar, nearby, unpolluted soil. In some cases, soil contaminant levels may be acceptable if the soil does not produce leachate with concentration levels above drinking water standards. Such determinations are often based on a test called the Toxics Characteristic Leaching Procedure, which mildly acidifies and agitates the soil, followed by chemical analysis of the leachate. Contaminant levels in the leachate below the maximum contaminant levels (MCLs) in the federal Safe Drinking Water Act are considered acceptable. Finally, soil contaminant levels may be set in a determination of health risks based on typical or worst case exposures. Exposures can include the inhalation of soil as dust, ingestion (generally by small children), and direct skin contact. The flexible definition of acceptable toxicity levels reflects the complexity of contaminant mobility and toxicity in soil, and the difficulty of pinning down acceptable and safe levels.