This chart (click chart for larger version) shows the levels of tritium in Ferry Creek on the Fermilab site since April 2006. To date, Fermilab has not detected tritium in Ferry Creek. The detection limit is one picocurie per milliliter (see footnote). During droughts, Ferry Creek can be dry at the Fermilab site boundary and we can not take water samples.
Increased monitoring began on Ferry Creek following the detection of low levels of tritium in Indian Creek in November 2005. The levels of tritium in the Fermilab cooling ponds and in Indian Creek are well below the federal water standards for tritium. Fermilab continues to monitor the ponds and creeks on its site and take steps to keep the levels of tritium as low as reasonably achievable.
State of Illinois agencies have taken water samples from Indian Creek in the past. Comparing those results with Fermilab's results for Indian Creek confirmed the accuracy of Fermilab's measurement system.
About the graph: A solid dot appears on every day in which a sample has been taken and analyzed. For samples in which a level of tritium above the limit of detection has been measured, the uncertainty of the measurement is indicated by an error bar attached to the solid dot. Samples with no detectable level of tritium are represented by a solid dot without error bar at the bottom of the graph.
Footnote: A picocurie is the unit used to specify how many tritium particles in a water sample decay into helium particles each second. Standard tests can detect levels of tritium in water that are larger than about 1 picocurie per milliliter. The Department of Energy surface water standards specify a limit of 1900 picocuries per milliliter.