CONTINUOUS MONITORING OF INCREASING ROAD SALT CONCENTRATION IN GROUND WATER IN AN ACTIVE PUMPING FIELD IN MASSACHUSETTS
Several important trends of de-icing contaminations can be presently identified: (1) lasting aquifer stratification; (2) seasonal variations; and (3) continually increasing concentration from year to year.
The data record show vertical stratification of the aquifer where the upper zone has larger amounts of dissolved deicing chemicals (250 ppm) than the lower zone (150 ppm). This superposition does not change over the study period (Mar ’11 – Aug ’12).
The data show an increase in specific conductance of 25% during the late summer and a minimum during early spring. Although this pattern appears in all sensors, it is particularly noted for the upper part of the aquifer which is likely due to increased evapotranspiration.
One of the most critical observations is the continual rise of the salinity in the lower zone of the Norwell aquifer. In March 2011 the chloride concentrations (calculated from calibrated chloride vs. specific conductance measurements) were 155 ppm of Cl and in the summer of 2012 the concentration of chloride for the first time exceeded 180 ppm. The 12 month increase equals to 11 ppm of Cl/y. At this rate the entire aquifer will eclipse the secondary drinking water standard for chloride in just 6 years!