Anticipating ground-water contamination by new technologies and chemicals:The case of chlorinated solvents in California

The discovery of the widespread contamination of the Californian alluvial-b asin aquifers by plumes of dissolved-phase chlorinated solvents (TCE, CFCs, TCA, PCE) in the period 1979-1981 was partly the result of recommended ind ustrial waste-disposal practices during the preceding decades. In order for the present contamination to have been anticipated and minimized, several conditions would all have to have been met by about 1950, First, chlorinate d solvents would have to have been identified as potential drinking-water c ontaminants such that the disposal of chlorinated solvents on dry soil woul d have been prohibited (or strictly regulated) and accidental spills rapidl y cleaned up. Second, monitor-well networks would have to have been operati onal up-gradient of water-supply wells and near solvent-using facilities, a nd gas-chromatographic methods capable of detecting aqueous contamination w ell below 1 ppm would have to have been in widespread use. Third, a paradig m explaining the subsurface migration and fate of dense nonaqueous phase li quids would have to have been published and widely accepted at approximatel y the same time as the identification of chlorinated solvents as potential drinking-water contaminants. Unfortunately, the first two of these conditio ns were not met until the 1970s and the third not until the 1980s, Furtherm ore, all three conditions were not only necessary, but also were complement ary requirements for the anticipation of ground-water contamination in the Californian basins.