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

The quality of groundwater used by rural residents of St. Lawrence County, New York is largely unknown. While some residents may have tested domestic well and spring water for contaminants such as coliform bacteria during property transactions, the diverse geology of St. Lawrence County creates a potential for contamination from natural inorganic trace elements and metals. The first phase of this countywide pilot study, completed in August 2007, sampled groundwater from 60 private wells and springs in 16 of the 33 county municipalities. Water samples were obtained from interested homeowners who answered a groundwater questionnaire. Samples were analyzed for 72 inorganic metal and trace elements using Inductively Coupled Plasma Mass Spectrometry. Overall, the first 60 samples imply that the county's groundwater is generally of good quality with only three wells exceeding the U.S. EPA's Primary Maximum Contaminant Level (MCL) for arsenic (10.2 ppb), copper (1435.1 ppb), and uranium (30.6 ppb), respectively. Nuisance metals such as manganese (n = 6), however, were sometimes present at concentrations that may aesthetically alter drinking water and are above the EPA secondary MCLs. Use of Geographic Information Systems (ESRI ArcGIS 9.2) to build a geodatabase and later analyze trends shows the potential for geochemical differences between the more carbonate-rich Paleozoic rocks of St. Lawrence Lowlands and the Precambrian crystalline rocks of the Adirondack Lowlands and Highlands. Because of the variable thickness of glacial and post-glacial fluvial deposits, deriving correlations between bedrock geology and groundwater geochemistry are difficult without accurate well depth measurements and boring logs. Nonetheless, elevated concentrations above background levels of boron (1191 ppb), lithium (32.2 ppb), and strontium (8214.86 ppb) in groundwater near the Power's Farm tourmaline deposit suggest that groundwater studies may be an effective tool for understanding the spatial distribution of minerals and rock units in this area despite the glacial cover. Preliminary results also have identified a band of wells with elevated (but largely below EPA MCLs) concentrations of arsenic within the Lower Paleozoic units of the St. Lawrence Lowlands.