Publication Summary

Recent information indicates the presence of several Whidbey Island wells producing water with high chloride levels from aquifer zones above sea level. Seventeen suspect wells, six control wells, and two ocean locations were sampled during the investigation. Field measurements indicate that only 20 of the 23 sampled wells are actually completed above sea level. Several methods were utilized to analyze for the presence of seawater. These included constructing Stiff diagrams, hardness and chloride versus specific conductivity plots, and Piper diagrams. Study results suggest that 16 of the 23 wells produce water with chemical compositions resembling very hard ground water rather than dilute seawater. Of the various methods used during the study, Stiff diagrams and chloride hardness versus conductivity plots appear to be the simplest and most reliable for distinguishing very hard ground water from ground water influenced by seawater. It is possible to produce chemistry resembling that of dilute seawater by contaminating very hard water with man induced nutrients. Consequently, water samples were analyzed for nitrates and other nutrients. Of the 23 sampled wells, seven produced water with nitrite plus nitrate nitrogen concentrations exceeding 2 mg/L. A comparison indicated that three of these seven wells were also included as one of the seven wells which produced water with chemical compositions resembling dilute seawater. Of the remaining four wells, two are completed significantly below sea level, and one appeared to be seawater influenced according to only one of the four graphical techniques. Taking into consideration all known well information, it appears likely no more than one or two of the 20 above sea level wells may actually be influenced by seawater. The source(s) of the seawater component(s) for these wells is unknown, but possibilities include irrigation with saline water, sea spray, and dilution with relict water.