AQUIFER STRATIFICATIONS OF WATER QUALITY PARAMETERS IN URBANIZED AREAS OF EASTERN MASSACHUSETTS

Salinization of aquifers and deterioration of water quality in the public water supply areas has been attributed to road salt applications on road surfaces during the winter seasons in many northern tier states of the continental USA. Of interest to this study is the imbalance between the annual road salt input into the watersheds and road salt removal as annual dissolved load by the stream flow. Approximately 50% of the applied annual road salt load cannot be accounted for by the present models.

We report on data from a suite of direct-push drill holes sampled at 10 ft intervals throughout the groundwater section constituting up to 80 ft deep vertical profiles. The drill holes are located a short distance downgradient from a Department of Public Works road salt storage and maintenance yard used for storage and loading trucks during the winter months. Road salt is stored year round. Three of the most proximal wells have steep chloride gradients: from low levels (2 to 200 ppm) at the GW surface increasing sharply with depth to 760 and 1178 ppm, respectively, at the base, 70 to 90 ft below GW surface. Highly concentrated saline solutions predictably percolate into the aquifer environment, and when they reach the groundwater surface, they will continue to migrate further through the GW column due to their higher saline solution density until the solutions reach the aquifer base (unconsolidated glacial deposits). Reasonably estimates based on observed concentrations and temperatures the percolating saline solutions have densities in the 1.02 to 1.08 range. It is likely that similar saline densities may form near highways and parking lots and that the saline solutions accumulate near the aquifer base. Such process would explain the observed disparities between the annual road salt loading and the deficit of annual road salt removed as dissolved load. The model is also consistent with the observed gradual annual increase of 1 to 4 ppm of chloride concentration in monitored streams despite a level road salt application rates in the recent years.