Tritium in Ohio's Ground Water

Tritium is a radioactive isotope of hydrogen with a half-life of 12.43 years. It is produced naturally in the atmosphere by cosmic radiation (neutron bombardment of nitrogen). Tritium combines with oxygen to form tritiated water in the stratosphere and eventually falls to the earth as precipitation. It is estimated that the natural atmospheric tritium concentrations ranged from 2 to 8 Tritium Units depending on geographic location. Beginning in 1953 and continuing through the early 1960's, tritium concentrations in the atmosphere increased by up to three orders of magnitude in the northern hemisphere because of nuclear weapons testing. This increase in tritium makes it a useful tracer for at least 50 to 70 years.

Tritium analyses of ground water can be used to determine if the aquifer has been in contact with the atmosphere in the last 50 years. If the analyses is below detection, it may be concluded that the ground water has not been recharged with post-1950 "bomb enriched" tritium. Tritium cannot be used to precisely age date water; it can only illustrate if water contains pre-1950 or post-1950 precipitation.

A total of 160 raw water samples were collected from Ambient wells during the Spring 1997 sampling round and analyzed for tritium, as shown regionally on the tritium concentration map. These wells are all large capacity community public water systems utilizing ground water. The analytical results ranged from non-detect (histograms showing the distribution by aquifer type and by total well depth.

Histograms of Tritium Concentrations in Ohio's Ground Water

Tritium concentrations for the ambient ground water quality PWS's shown by (a) range of concentrations, (b) range of concentrations by aquifer type, and (c) range of concentrations by total depth of well. Note the bimodal distribution.