The concentrations of tritium, helium isotopes, and neon have been mea
sured in ground mater from a fractured bedrock aquifer in a densely po
pulated suburban area near New York City, Samples were obtained from h
eavily pumped production wells of a regional water supply company. Hel
ium and neon concentrations exceed the values for air-saturated water,
which is explained by the addition of unfractionated atmospheric air,
radiogenic helium, and tritiogenic He-3. The identification of the co
mposition of these excess components allows reliable separation of the
tritiogenic He-3 concentration, and hence the calculation of the H-3/
He-3 ages of the ground water, Comparison of the combined tritium plus
tritiogenic He-3 concentrations with the historical record of tritium
input from precipitation confirms that the H-3/He-3 data are self-con
sistent and provides constraints on the degree of mixing or helium los
s. The distribution of H-3/He-3 ages is related to the large-scale top
ography of the study area and the depth of the wells. Furthermore, cor
relations between the H-3/He-3 ages and concentrations of total dissol
ved solids and total CO2 show that the ages contain meaningful informa
tion related to the temporal changes of the ground water chemistry.