SEASONAL VARIATION OF GROUNDWATER CHEMISTRY IN NORTHWESTERN MONROE COUNTY, NEW YORK

A synoptic study of domestic well water supplies in northwestern Monroe County, NY reveals the range of major ion water chemistries at different sampling points within the lakeshore region, and apparent seasonal water-chemistry variations at some locations. Unconsolidated glacial till and outwash deposits form the shallow aquifer (< 20m) that supplies the screened intervals of the domestic supply wells in this study. These surficial deposits overlie Queenston Shale bedrock of the Upper Ordovician. Twelve sampling wells within region were monitored and sampled seasonally at approximately 2 month intervals. Surface water was sampled as available. Sites were analyzed for depth to water, total dissolved solids and major ion elemental analysis. Spatial and temporal changes in major ion chemistry may be due to upwelling of older groundwater diverted to the surface or the impact of road deicing salts commonly applied in the region. Spatial water chemistry trends within the region appear to be the result of upwelling associated with local fracture zones, possibly influenced by the regional Clarendon-Lyndon fault. The upwelling along the fractures supplies groundwater dominated by high TDS and chloride values in a limited area. Temporal variations, most pronounced in shallow wells located near roadsides, appear to be primarily due to changes caused by winter application of deicing salts or inversely the spring dilution of deicing residues. Results show a wide range of major ion concentrations within the study area. Total dissolved solids (TDS) and chloride, the dominant anion, were found to range from 88 to 3987 mg L-1 and 0.5 to 1887 mg L-1, respectively. Wells associated with a high TDS hot spot were found to increase in concentration from spring to summer while other wells showed decreasing concentrations. These results illustrate the inherent spatial and temporal variability of ground water chemistry in surficial aquifers due to upwelling of groundwater at depth and also displays the residence time of road deicing salts in groundwater supplies within highly transmissive glaciolacustrine surficial aquifers.