Scientific Investigations Report 2007–5169
By Todd S. Miller, Edward F. Bugliosi, Kari K. Hetcher-Aguila, and David A. Eckhardt
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 63 milligrams per liter slightly exceeded the U.S. Environmental Protection Agency’s Secondary Maximum Contaminant Level of 60 milligrams per liter. Five samples were collected from test and production wells near, and in, the southern well field and analyzed for concentrations of chlorofluorocarbons and tritium, to determine ground-water ages that ranged from approximately 25 years old or less.
Results from a three-dimensional, finite-difference, ground-water-flow model used to simulate ground-water flow in the Sandy Creek/Lacona study area indicated that (1) about 61 percent of recharge to the aquifer is from precipitation directly on the aquifer, 38 percent of recharge is from streamflow seeping into the aquifer, one percent is from unchanneled runoff and ground-water inflow from uplands, and (2) the majority (86 percent) of discharge from the aquifer is from ground-water seepage to the headwater tributaries west (downgradient) from the well fields with the remaining 14 percent discharging to streams, manmade ditches, and the two production wells in the central part of the aquifer. Little or no water pumped from the production well in the sand and gravel aquifer appears to be derived from bedrock because (1) a till layer on top of bedrock impedes flow between the sand and gravel aquifer and the underlying bedrock, (2) the hydraulic-head gradient between the two is downward, not upward, and (3) the water chemistry in each is different.
Ground-water particle-tracking results indicate that ground-water traveltimes are relatively short, generally taking less than 1.5 years for most of the water to flow from the eastern boundary of the aquifer to the southern well field. This is in contrast to geochemical age dates that indicate that water withdrawn from the southern well field is 13 to 17 years old. A plausible reason for the discrepancy in ground-water age might be that much of the recharge is relatively older water from upland sources. Possible upland sources of the relatively old water are (1) ground-water discharge from till and bedrock units that enters streams that drain the Tug Hill uplands during base-flow conditions, then lose water to the sand and gravel where they flow over the aquifer, and (2) ground-water inflow from adjacent till and bedrock uplands. Similarly, this discrepancy in ground-water age has been noted in another area of the state with a similar hydrogeologic setting where older stream water from the adjacent till and bedrock uplands was a source of recharge to the adjacent sand and gravel aquifer and contributed to the apparent age of the ground water.
1–2. Maps showing—
1. Location of Sandy Creek/Lacona and Pulaski study areas, physiographic provinces, and Tug Hill glacial aquifer
2. Surficial geology and location of production wells for the Village of Pulaski in Richland, N.Y.
3. Diagram of generalized geologic section A-A’ through part of Tug Hill glacial-drift aquifer at Richland, N.Y.
4. Map showing water table in the vicinity of the Pulaski well fields during fall of 2003
5–6. Graphs showing—
5. Temperature of water in Village of Pulaski dug well OW 493, piezometer OW 501, and adjacent stream from July 2003 through November 2004
6. Tritium decay curves for Ottawa, Canada and value of tritium in wells OW 497, OW 499, and OW 500 sampled on May 7, 2004 near Pulaski, N.Y.
7. Map showing surficial and bedrock geology, model boundary, and productionand test-well locations, and location of line of geologic section in the Sandy Creek/Lacona, N.Y. study area
8. Diagram of generalized hydrogeologic section B-B’ near Sandy Creek/ Lacona, N.Y.
9. Map showing streamflow measurements, ground-water-flow directions, surface-water seepage area, and production wells in the southern part of the Sandy Creek/Lacona aquifer, N.Y.
10. Diagram of wells and apparent ages of ground water determined by concentrations of chlorofluorocarbons in the villages of Sandy Creek and Lacona’s well field near Lacona, N.Y.
11. Map showing three-dimensional-flow model cells, simulated cell types, and location of conceptual section C-C’ for the Sandy Creek/Lacona, N.Y., study area
12. Diagram of conceptual generalized, cross-sectional representation of ground-water-flow model showing cell types and directions of recharge and discharge to the aquifer in the Sandy Creek and Lacona, N.Y. area
13–14. Maps showing—
13. Hydraulic conductivities for different aquifer deposits and model layers used in ground-water-flow model calibration
14. Water-table contours based on the calibrated, three-dimensional-flow-model output in the Sandy Creek/Lacona, N.Y. study area
15. Graph showing results of sensitivity analyses of hydraulic head in the sand and gravel aquifer in the Sandy Creek/Lacona, N.Y. study area
16a–b. Maps showing—
a. Simulated areas contributing to production wells pumping at 100 gallons per minute, derived from particle-tracking results based on calibrated, threedimensional- flow-model output in the Sandy Creek/Lacona, N.Y. study area
b. Simulated areas contributing to the southernmost production wells pumping at 200 gallons per minute, derived from particle-tracking results based on calibrated, three-dimensional-flow-model output in the Sandy Creek/Lacona, N.Y. study area
17. Conceptual diagram showing possible sources of older ground water recharging
the sand and gravel aquifer near Lacona, N.Y.
1. Inorganic and physical constituents of water samples from selected wells in the Pulaski, N.Y. study area, 2003–04
2. Concentrations of tritium, chlorofluorocarbon (CFC), and air-temperature correction data for wells in the Pulaski, N.Y. study area, 2003-04
3. Inorganic and physical constituents of ground water from wells in the villages of Sandy Creek and Lacona, N.Y. study area
4. Tritium, chlorofluorocarbon (CFC), and air-temperature correction data for wells in the Sandy Creek and Lacona, N.Y. study area
5a. Difference between measured and simulated heads at 11 selected non-pumped wells in the Sandy Creek/Lacona, N.Y. model study area
5b. Difference between measured and simulated streamflow in the Sandy Creek/Lacona, N.Y. model study area
6. Steady-state ground-water budget for the ground-water-flow model of the Tug Hill glacial-drift for average annual recharge conditions
Miller, T.S., Bugliosi, E.F., Hetcher-Aguila, K.K., Eckhardt, D.A., 2007, Hydrogeology of two areas of the Tug Hill glacial-drift aquifer, Oswego County, New York: U.S. Geological Survey Scientific Investigations Report 2007–5169, 42 p, online only.
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