Ground-Water Age Dating in Community Wells in Oswego County, New York
by Stephen C. Komor
U.S. GEOLOGICAL SURVEY
Open-File Report 01-232
ABSTRACT
Officials in Oswego County, in north-central
New York, have been concerned about potential
contamination of community wells. Many of
these wells are completed in unconfined glacial
sand-and-gravel aquifers, although some are
finished in till or in the underlying fractured and
jointed bedrock of Late Ordovician and Early
Silurian ages. Local shallow ground-water flow is
affected by the orientation and hydraulic
characteristics of the local topography and
surficial sediments, whereas deeper regional flow
is toward Lake Ontario. Concentrations of
chlorofluorocarbons and tritium in water samples
from 28 wells in the county were measured in
1999 for ground-water-age dating; results yield
recharge dates ranging from about 1955 to 1994.
The presence of water older than about 15
years in the sand-and-gravel aquifers differs from
previous concepts of recharge sources and
ground-water movement that were based on
numerical modeling of ground-water flow. Young
ground water (1 to 5 years old) probably
represents recharge from recent precipitation and
seepage from streams, whereas the oldest ground
water (more than 40 years old) probably is
derived from the fractured bedrock that underlies
the glacial sediments or has moved along long
flow paths in unconsolidated deposits, or through
poorly permeable material. Some sand-and-gravel
aquifers in Oswego County contain mixtures of
old and young water. Wellhead-protection efforts
need to focus on protection of the quality of
young water in the sand-and-gravel aquifers
because young water is more likely to be
contaminated than old water.
Citation: Komor, S.C., 2002,
Ground-Water Age Dating in Community Wells in Oswego County, New York:
U.S. Geological Survey Open-File Report 01-232, 16 p.
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