EARLY-INDICATOR SIGNALS OF GROUNDWATER CONTAMINATION - THE CASE OF SEAWATER ENCROACHMENT

An early indication of groundwater contamination occurs when pollutant concentrations start to fluctuate and exceed background values of amb ient fresh groundwater. An analysis of a characteristic situation of t his type uses data from Israel's coastal phreatic granular aquifer. Th e pollutant is generally seawater, and the contamination process invol ves replacement of freshwater by encroaching sea-or other saltwater, a process augmented by human activity. The contamination process involv es three stages: (1) groundwater composition remains relatively stable with small salinity content; (2) small salinity changes are perceptib le with reversible fluctuations; and (3) salinity concentration increa ses at a sharply higher rate. The second stage is a useful early-indic ator signal of contamination. Early-indicator signals of groundwater p ollutant concentrations involve ''minor'' fluctuations in water chemis try at the advent of the contamination process. The intensity and magn itude of such a salinization/pollution process at any given location d epends upon lithologic matrix, aquifer heterogeneity, and resultant fl ow domain characteristics, as well as contaminant properties. If such ''signs'' are detected at a sufficiently early stage, appropriate mana gement steps may be taken to rectify further seawater and/or saltwater encroachment.