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Scientific Investigations Report 2009–5173

Prepared in cooperation with the
Town of Caroline and Tompkins County Planning Department

Geohydrology and Water Quality of the Valley-Fill Aquifer System in the Upper Sixmile Creek and West Branch Owego Creek Valleys in the Town of Caroline, Tompkins County, New York

By Todd S. Miller


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In 2002, the U.S. Geological Survey, in cooperation with the Town of Caroline and Tompkins County Planning Department, began a study of the valley-fill aquifer system in upper Sixmile Creek and headwaters of West Branch Owego Creek valleys in the Town of Caroline, NY. The purpose of the study is to provide geohydrologic data to county and town planners as they develop a strategy to manage and protect their water resources. The first aquifer reach investigated in this series is in the Town of Caroline and includes the upper Sixmile Creek valley and part of West Branch Owego Creek valley. The portions of the valley-fill aquifer system that are comprised of saturated coarse-grained sediments including medium to coarse sand and sandy gravel form the major aquifers. Confined sand and gravel units form the major aquifers in the western and central portions of the upper Sixmile Creek valley, and an unconfined sand and gravel unit forms the major aquifer in the eastern portion of the upper Sixmile Creek valley and in the headwaters of the West Branch Owego Creek valley.

The valley-fill deposits are thinnest near the edges of the valley where they pinch out along the till-mantled bedrock valley walls. The thickness of the valley fill in the deepest part of the valley, at the western end of the study area, is about 100 feet (ft); the thickness is greater than 165 ft on top of the Valley Heads Moraine in the central part of the valley.

An estimated 750 people live over and rely on groundwater from the valley-fill aquifers in upper Sixmile Creek and West Branch Owego Creek valleys. Most groundwater withdrawn from the valley-fill aquifers is pumped from wells with open-ended 6-inch diameter casings; the remaining withdrawals are from shallow dug wells or cisterns that collect groundwater that discharges to springs (especially in the Brooktondale area). The valley-fill aquifers are the sources of water for about 200 households, several apartment complexes, two mobile home parks, a school, and several farms and small businesses. Most groundwater that is withdrawn from pumped wells is returned to the groundwater system via septic systems.

Groundwater in the upper and basal confined aquifers in the upper Sixmile Creek valley is under artesian conditions everywhere except where the water discharges to springs along bluffs in the western end of the Sixmile Creek valley. Principal sources of recharge to the confined aquifers are (1) the sides of the valley where the confined aquifers may extend up along the flank of the bedrock valley wall and crop out at land surface or are overlain and in contact with surficial coarse-grained deltaic and fluvial sediments that provide a pathway through which direct precipitation and seepage losses from tributary streams can reach the buried aquifers, or (2) where the buried aquifers are isolated and receive recharge only from adjacent fine-grained sediment and bedrock.

The base-flow and runoff components of total streamflow at two streamgages, Sixmile Creek at Brooktondale and Sixmile Creek at Bethel Grove, were calculated using hydrograph-separation techniques from 2003 to 2007 discharge records. Base flow constituted 64 and 56 percent of the total annual flow at the Brooktondale and Bethel Grove streamgages, respectively.

Water-quality samples were collected from 2003 to 2005, with 10 surface-water samples collected seasonally during base-flow conditions at the Sixmile Creek at Brooktondale streamgage, and 12 samples were collected during base-flow conditions at several selected tributaries from 2004 to 2005. The predominant cation detected in the surface-water samples was calcium, but moderate amounts of magnesium, silica, and sodium were also detected; the major anions were bicarbonate, chloride, and sulfate. Sodium and chloride concentrations were relatively low in all samples but increased downstream from the Sixmile Creek sampling site at Six Hundred Road near Slaterville Springs, NY, to Brooktondale, NY; some of the increases may be attributed to road salt, but most are probably natural discharge of brackish water originating from deep zones in the bedrock that discharge upward into the valley-fill aquifer. The concentration of nitrate was less than 1.0 milligram per liter (mg/L) in all stream samples taken during base-flow periods except in the tributary to Sixmile Creek at Slaterville Springs on July 19, 2005, when the concentration was 1.91 mg/L. Flow in this tributary during the summer originates from groundwater discharging from Valley Heads Moraine, which has large areas used for agriculture.

Groundwater samples were collected from 10 wells—9 finished in sand and gravel aquifers and 1 finished in bedrock. Results of the groundwater sample analyses indicate the water is generally of good quality. Water in the sand and gravel aquifers is predominantly of the calcium-bicarbonate type. The cation detected in the highest concentrations was calcium; values ranged from 25.8 to 80.1 mg/L. Sodium values ranged from 2.6 to 106 mg/L; two samples exceeded the U.S. Environmental Protection Agency Drinking Water Advisory (30 to 60 mg/L) for sodium. Variations in sodium concentrations were probably due to either local enrichment through road de-icing salts or brackish water from bedrock that locally discharges to the valley. Nitrate concentrations in five of nine samples collected from the valley-fill aquifer were below the detection limit of 0.060 mg/L; concentrations ranged from 0.239 to 2.68 mg/L in the four wells that had concentrations above the detection limit.

Three groundwater samples were collected and analyzed for chlorofluorocarbons (CFCs) and 3H to determine groundwater age. The results of the CFC and 3H samples indicated that the apparent age of the water from the flowing well at the Caroline Town Hall was early to late 1950s; in the shallow test well (39 ft deep) at the Caroline Elementary School, early-to-late 1970s; and from the deep test well (TM1967) at the school, early-to-late 1950s.

The reported yields by water-well drillers were greater for the unconfined sand and gravel aquifer—a median of 15 gallons per minute—than for the confined aquifers—a median of 12 gallons per minute. Bedrock wells generally had smaller yields (median 6 gallons per minute) than the valley-fill aquifers. The mean well depths for the various aquifer types were: 42 ft for the unconfined sand and gravel aquifer, 64 ft for the confined sand and gravel aquifers, and 149 ft for bedrock aquifers.

First posted December 2009

For additional information contact:
U.S. Geological Survey
New York Water Science Center
425 Jordan Road
Troy, NY 12180

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Suggested citation:

Miller, T.S., 2009, Geohydrology and water quality of the valley-fill aquifer system in the upper Sixmile Creek and West Branch Owego Creek valleys in the Town of Caroline, Tompkins County, New York: U.S. Geological Survey Scientific Investigations Report 2009–5173, 56 p.




Purpose and Scope

Description of Study Area

Previous Studies

Data Collection

Geologic Data

Seismic-Refraction Surveys

Well Inventory, Test Drilling, Groundwater-Level and Streamflow Measurements

Water-Quality Sampling and Analysis


Bedrock Scouring

Wisconsinan Drift

Depositional Facies

Facies 1—Ice-Contact Deposits

Facies 2—Proglacial Lake Deposits

Facies 3—Late- and Post-Glacial Deposits

Valley Heads Readvance

Hydrology of the Valley-Fill Aquifer System

Aquifer Geometry

Unconfined Aquifers

Confined Aquifers and Confining Units

Bedrock Aquifers

Groundwater Levels and Flow Paths

Climate Response Network Well

Groundwater Recharge

Unconfined Aquifers

Direct Infiltration of Precipitation on the Valley Floor

Unchanneled Runoff and Groundwater Inflow from Adjacent Hillsides

Seepage Losses from Upland Tributaries

Confined Aquifers

Groundwater Discharge

Seepage to Streams


Sixmile Creek

Pumped Withdrawals and Water Availability

Breaching of the Confining Unit at Slaterville Springs

Water Quality

Surface Water

Physical Properties

Common Inorganic Constituents



Physical Properties

Common Inorganic Constituents


Groundwater Age Dating


References Cited

Appendix 1

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