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Soil background concentrations are important to consider when conducting human health and ecological risk assessments. Regulators use soil values specific to contaminants commonly found in soil to evaluate whether they will pose risks to people or the environment. These soil values are risk-based values; they are derived using toxicity data, exposure parameters, and chemical specific parameters. For some chemicals, purely risk-based values are below what is found in our soils from natural or ambient sources. In these cases, since it is not common practice to require regulated parties to take action if the amount of the chemical in soil is less than background, regulators often allow soil background values to be used instead of the risk-based values.
There is inconsistency in the way stakeholders define background, use sampling methods, and apply statistical methods in risk assessment. Other sources of valuable information such as geochemical evaluations and forensic methods are not widely used or accepted. Although some states, federal agencies, and other entities have guidance documents regarding this subject, there is no comprehensive up-to-date guidance or a summary of existing resources applicable widely to most sites. The ITRC guidance document and training resources produced by this team will provide a useful framework for using soil background concentrations in risk assessment and its application to soil-like materials and mining sites.
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