[en] Three unlined impoundments were formerly used to collect and, in some instances, treat wastewater generated at Oak Ridge National Laboratory (ORNL). They are (1) the 3513 Waste Holding Basin, (2) the Old Hydrofracture Facility (OHF) impoundment, and (3) the Homogeneous Reactor Experiment No. 2 (HRE) impoundment. To determine if the migration of contaminants from these impoundments presents a threat to groundwater quality, at least one upgradient groundwater monitoring well and three downgradient monitoring wells were installed in 1985. Groundwater monitoring during 1986 and 1987 revealed that the principal contaminants found in groundwater downgradient from the impoundments were radionuclides, namely ⁹⁰Sr and tritium. Previous groundwater monitoring was focused largely on analyses of groundwater for toxic metals (Ag, As, Ba, Cd, Cr, Hg, Pb, Se), other constituents contained in EPA's primary drinking water standards, and radionuclides. Other than the analyses for total organic carbon and total organic halides, little attention was given to the detection of hazardous organic compounds in groundwater. The major objective in the 1988 sampling at these impoundments was to determine if hazardous organic compounds, namely volatile and semivolatile organics, are leaching into groundwater from these impoundments