Occurrence of chlorinated solvents in a pristine aquifer system

The occurrence of chlorinated solvents was studied in the groundwater from a pristine aquifer system at Klosterhede, Denmark. Although this location is remote from industrial emissions and free of point sources of soil and groundwater, high concentrations of chloroform (up to 1.6 mu g L-1) and low concentrations of trichloroethene, tetrachloroethene and 1,1,1-trichloroethane (less than 0.01 mu g L-1) were found. Supported by field and laboratory studies of the occurrence and release of chlorinated solvents from forest soil, a natural formation is suggested for chloroform whereas the other chlorinated compounds investigated probably resulted from atmospheric deposition. The natural formation in the soil caused chloroform concentrations in the groundwater that approached levels of public concern.