A STUDY OF THE DRASTIC METHODOLOGY WITH EMPHASIS ON SWEDISH CONDITIONS

A study of the DRASTIC classification methodology, with special emphasis on Swedish conditions, indicated both favorable and unfavorable properties of the system. The study showed that the fairly large number of parameters (seven) and the correlations between these parameters give DRASTIC some advantageous statistical properties. A comparison of the DRASTIC parameters with parameters found to determine the effects on ground-water quality in surficial aquifers in southwestern Sweden from acid deposition showed a good agreement between these two parameter sets; the study thus indicated that the selection of parameters is relevant for general ground-water vulnerability assessments in Sweden. The concept of hydrogeologic settings and the possibility to trace results backwards in the system is excellent, but the qualitative weight functions in DRASTIC result in a simplistic index of unclear meaning that is less useful and less distinctive than desired. The system tends to overestimate the vulnerability of porous media aquifers compared to aquifers in fractured media; the rating tables need to be revised so that more weight is given to specific surface and effective porosity, and less to hydraulic conductivity. The applicability of the results would be enhanced and the risk of misuse reduced if the results were more clearly directed toward scientifically defined factors, e.g. sorption capacity, travel time, and dilution.