DETERMINATION OF BACKGROUND CONCENTRATIONS OF INORGANICS IN SOILS ANDSEDIMENTS AT HAZARDOUS-WASTE SITES

Hazardous waste sites may pose a threat to human health and the enviro nment when toxic substances are released. However, the contaminants pr esent at a waste site may have originated 'on-site' (i.e., resulting f rom releases attributable to site activities) or 'off-site' (i.e., res ulting from sources not on-site). Off-site substances may result eithe r from natural sources (e.g., erosion of naturally occurring mineral d eposits) or anthropogenic sources (e.g., widespread contamination from automobile exhaust in urban areas). To determine the appropriate acti on to take at a hazardous waste site, the U.S. Environmental Protectio n Agency (EPA) must distinguish between substances directly attributab le to the hazardous waste site (i.e., site contaminants) and those att ributable to natural background concentrations. The most important fac tor to consider when determining background concentrations is to ensur e that the physical, chemical, and biological aspects of the media to be sampled at both the contaminated site and the background site are a s similar as possible. Inorganics, in particular metals, are addressed . Radionuclides are not specifically addressed; however, metals with r adioactive isotopes that may be encountered at hazardous waste sites a re included. There are references and data included in this paper that provide average concentrations and reference values for selected soil s and sediments in the United States. Suggested sampling and monitorin g design approaches that could be used by scientists and engineers fac ed with how to determine background concentrations are identified. The issues discussed include the selection of background sampling locatio ns, considerations in the selection of sampling procedures, and statis tical analyses for determining whether contaminant levels are signific antly different on a potential waste site compared with a background s ite.