TEMPORAL AND SPATIAL TRENDS IN THE SALT CONTENT OF CONNECTICUT'S GROUNDWATER OVER THE LAST 100 YEARS

Groundwater impacts from road and sidewalk salting, landfill discharges and salt water intrusion have been ongoing for decades as the population of Connecticut has grown and land use changes have occurred. More recently efforts to reduce runoff through the use of rain gardens, permeable pavement, and evaporation ponds may also contribute salt to groundwater. To evaluate the salt impact of these measures, we are compiling and synthesizing in ArcGIS statewide groundwater quality data going back to 1895. The historical turn of the century data reveal a baseline trend of decreasing salt content northward from Long Island Sound, with a range in chloride concentration from about 1 to 4 mg/l, averaging about 2 mg/l. Recent raw water quality data from public drinking water wells demonstrate the change in chloride concentrations which range from 1 to 1500 mg/l, averaging about 44 mg/l. In addition to point sources of salt, large areas are exhibiting elevated salt levels, especially in the central portion of the State. The increase in salt concentration is not just confined to shallow stratified drift aquifers but also can been seen in data for bedrock wells in fractured crystalline bedrock. In the latter case, concentrations of salt appear to increase in the summer months, perhaps owing to the lowering of the water table where salt concentrations decrease with depth in the overburden. Spatial trends also show that that the groundwater salt content in some rural areas has not change in over a hundred years.