Using Electronic Conductivity and Hardness Data for Rapid Assessment of Stream Water Quality

A graphical screening method was previously developed for rapidly assessing stream water quality utilizing a plot of specific conductance or electrical conductivity (EC) against concurrent alkalinity data. The plot is used to distinguish EC values for impacted or degraded streams from those that can be considered background values in a particular geologic setting. The method works well in areas underlain by carbonate bedrock, as streams in those areas characteristically have high EC and alkalinity values. However, in areas of low stream alkalinity (less than approximately 50 mg/L as CaCO₃), the method is much less effective. This paper extends the method by using the stream EC vs. total hardness (TH) correlation in regions of low alkalinity, specifically areas underlain by shale and other clastic sedimentary bedrock. A baseline relationship of EC vs. TH under baseflow conditions is created using surface water chemistry data from relatively undisturbed streams of the Catskill region of New York and northern Pennsylvania. The revised graphical screening method's usefulness is then demonstrated by application to stream chemistry data collected from the lower Delaware River basin. Although applied locally for demonstration, the method can generally be applied to other regions underlain by similar types of bedrock.