Estimation of Recharge Rates to the Sand and Gravel Aquifer Using Environmental Tritium, Nantucket Island, Massachusetts

U.S. Geological Survey, Water-Supply Paper 2297

Jayne Fifield Knott and Julio C. Olimpio

Table of Contents




Purpose and Scope

Location and physical setting


Geohydrology of the sand and gravel aquifer on Nantucket

Choice of the aquifer

Description of the study sites

Field instrumentation

Hydrologic factors influencing well design and sampling interval

Description of observation wells and water samplers

Estimation of recharge rates using tritium

Source of tritium

Tritium as a ground-water tracer


Tritium input function

Tritium concentrations in Nantucket ground water

Calculation of the average annual recharge rate

Evaluation of the results of the tritium method

Discrepancy between calculated and observed tritium concentrations

Statistical uncertainty

Comparison of the tritium estimates with other recharge-rate estimates

Analysis of water-table fluctuations

Thornthwaite method

Recharge rates in southeastern Massachusetts

Summary and conclusions

Selected references

Metric conversion factors


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