AN INVESTIGATION OF THE INORGANIC GEOCHEMISTRY AND DRINKING WATER QUALITY OF GROUNDWATER IN ST. LAWRENCE COUNTY, NEW YORK

A multi-element study of groundwater quality in St. Lawrence County, a large (7306 km2) and sparsely populated (112,000), rural, largely forested county in northern New York, has been carried out. Bedrock varies from south to north across the county from Precambrian crystalline granulite facies gneisses of the Adirondack Highlands, to mid-upper amphibolites facies metasedimentary rocks and intrusive granitoids of the Adirondack Lowlands, to flat-lying Paleozoic sandstones and dolostones of the St. Lawrence River Valley. A total of 99 groundwater samples were collected from private well owners between July and August 2008. The samples have been analyzed for seventy-two inorganic metal and trace elements by Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). ICP-MS results have been incorporated into an existing ArcGIS geodatabase containing data from 60 previously analyzed samples collected in June and July of 2007. Element concentration trend maps have been produced for the entire county on ArcGIS using Inverse Distance Weighted (IDW) interpolation and have been superimposed onto a St. Lawrence County bedrock map to determine the influence of the underlying bedrock on groundwater geochemistry and quality. Preliminary results suggest that the bedrock has a strong influence on groundwater geochemistry in many areas of St. Lawrence County. Examples include elevated B, Br, Li and Sr in dolostones with evaporitic layers; Na, Cl, S, and Zn associated with metamorphosed evaporate-carbonate hosted zinc deposits at Balmat; As along the Precambrian-Cambrian contact; and B and Li associated with world-class tourmaline deposits at Power's Farm. In addition, Ca and Mg are abundant in groundwater derived from marbles and dolostones which underlie large areas of the county. Results have been compared to the Environmental Protection Agency's (EPA) Maximum Contaminant Levels (MCLs) of primary and secondary standard regulations for drinking water. One sample exceeded the primary drinking water regulation for Arsenic while a total of thirty samples exceeded secondary drinking water standards: aluminum (n = 1), chlorine (n = 7), copper (n =5), iron (n = 1), manganese (n = 10), and total dissolved solids (n = 6). A pilot strontium isotope study is planned for January 2009 to further constrain the source of various waters.