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T his report identifies individual contaminants and contaminant mixtures that have beenmeasured in the ground at 91 waste sites at 18 U.S. Department of Energy (DOE) facilities within the weapons complex. The inventory of chemicals and mixtures was used to identify generic chemical mixtures to be used by DOE’s Subsurface Science Program in basic research on the subsurface geochemical and microbiological behavior of mixed con-taminants (DOE 1990a and b). The generic mixtures contain specific radionuclides, metals, organic ligands, organic solvents, fuel hydrocarbons, and polychlorinated biphenyls (PCBS) in various binary and ternary combinations. The mixtures are representative of in-ground contaminant associations at DOE facilities that are likely to exhibit complex geochemical be-havior as a result of intercontaminant reactions and/or microbiologic activity stimulated by organic substances. Use of the generic mixtures will focus research on important mixed con-taminants that are likely to be long-term problems at DOE sites and that will require cleanup or remediation. The report provides information on the frequency of associations among different chemi-cals and compound classes at DOE waste sites that require remediation. For example, radionuclides such as uranium, plutonium, strontium, and cobalt were found, in some cases