Hydrogeology of Two Areas of the Tug Hill Glacial-Drift Aquifer, Oswego County, New York

Two water-production systems, one for the Village of Pulaski and the other for the Villages of Sandy Creek and Lacona in Oswego County, New York, withdraw water from the Tug Hill glacial-drift aquifer, a regional sand and gravel aquifer along the western flank of the Tug Hill Plateau, and provide the sole source of water for these villages. As a result of concerns about contamination of the aquifer, two studies were conducted during 2001 to 2004, one for each water-production system, to refine the understanding of ground-water flow surrounding these water-production systems. Also, these studies were conducted to determine the cause of the discrepancy between ground-water ages estimated from previously constructed numerical ground-water-flow models for the Pulaski and Sandy Creek/Lacona well fields and the apparent ground-water ages determined using concentrations of tritium and chlorofluorocarbons.

The Village of Pulaski withdrew 650,000 gallons per day in 2000 from four shallow, large-diameter, dug wells finished in glaciolacustrine deposits consisting of sand with some gravelly lenses 3 miles east of the village. Four 2-inch diameter test wells were installed upgradient from each production well, hydraulic heads were measured, and water samples collected and analyzed for physical properties, inorganic constituents, nutrients, bacteria, tritium, dissolved gases, and chlorofluorocarbons.

Recharge to the Tug Hill glacial-drift aquifer is from precipitation directly over the aquifer and from upland sources in the eastern part of the recharge area, including (1) unchannelized runoff from till and bedrock hills east of the aquifer, (2) seepage to the aquifer from streams that drain the Tug Hill Plateau, (3) ground-water inflow from the till and bedrock on the adjoining Tug Hill Plateau.

Water-quality data collected from four piezometers near the production wells in November 2003 indicated that the water is a calcium-bicarbonate type with iron concentrations that slightly exceeded the U.S. Environmental Protection Agency?s Secondary Maximum Contaminant Level in three of the four samples. The relatively small concentrations of major ions and nutrients in the samples indicate that there is no contamination from septic-tank effluent and dissolved road salt in the ground water at the Village of Pulaski well field. Three of the four samples were analyzed for total coliform bacteria and Escherichia coli (E. coli), and only total coliform bacteria were detected in all three samples. E. coli was not detected in any samples.

The Villages of Sandy Creek and Lacona use about 270,000 gallons of water per day for public consumption?alternating withdrawals from northern and southern well fields located in glaciolacustrine beach, glaciofluvial outwash, and alluvial inwash deposits consisting mostly of silty sand and gravel. Four test wells were drilled, hydraulic heads were measured, and water samples collected between 2001 and 2003 and analyzed for physical properties, inorganic constituents, nutrients, bacteria, tritium, dissolved gases, and chlorofluorocarbons.

The aquifer in the Sandy Creek/Lacona area is highly susceptible to contamination because the aquifer (1) is unconfined, (2) is highly transmissive, (3) is thin (10 to 25 feet) and narrow (about 0.5 miles wide), and (4) has relatively short ground-water flowpaths from recharge to discharge areas (including wells). Additionally, drainage ditches east of the southern well field intercept westward-flowing ground water, which then is routed to an area just upgradient from the production wells where some of the water seeps back into the aquifer and is captured by these wells, effectively shortcircuiting the ground-water-flow system.

Water-quality samples collected from three wells in the Sandy Creek/Lacona southern well field indicate that the ground water is a sodium-bicarbonate/sulfate type and of good quality; however, in one water sample, the sodium concentration of 6