Occurrence of 224Ra, 226Ra, 228Ra, gross alpha, and uranium in California groundwater.

One hundred and twelve groundwater wells sampled from all the major aquifers in California were analyzed for 224Ra, 226Ra, 228Ra, gross alpha, and uranium. The results showed that radium is found in relatively low concentration, 1.56 x 10(-2)-1.23 Bq L(-1) (0.42-33 pCi L(-1)) for 224Ra, 2.2 x 10(-3)-0.81 Bq L(-1) (0.06-22 pCi L(-1)) for 226Ra, and 8.5 x 10(-3)-1.31 Bq L(-1) (0.23-35 pCi L(-1)) for 228Ra in California groundwater. Uranium was found at the highest concentration on both mass and activity basis and was correlated with the gross alpha measurement. Short-lived radioisotopes showed no significant contribution to gross alpha measurements. There was a strong correlation between 224Ra and 228Ra activities, suggesting the latter to be an indicator for the occurrence of the former. Comparison of 226Ra to 238U, 224Ra to 226Ra, and 226Ra to 228Ra showed scattered data indicating no correlation between each of these isotope pairs. Approximately 4% of the wells were found to exceed the U.S. Environmental Protection Agency (EPA) established maximum contaminant level for total radium of 0.185 Bq L(-1) (5 pCi L(-1)). Analysis of 228Ra by gamma-ray spectroscopy was in good agreement with the U.S. EPA-approved procedure.