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OCCURRENCE AND DISTRIBUTION OF 210Pb AND 210Po IN SELECTED CALIFORNIA GROUNDWATER WELLS

Groundwater wells from across the State of California were sampled and analyzed for 210Pb and 210Po. The separation method involved Fe(OH)3 precipitation from a 5-L groundwater sample followed by electrodeposition of 210Po on a nickel disk. The resulting solution was passed through an ion-exchange resin column for the isolation of 210Pb. De-ionized water spiked at a concentration range from 4.92 mBq L−1 to 755 mBq L−1 with these radionuclide standards showed excellent accuracy and precision of the method. In the groundwater wells, overall activity of 210Pb ranged from 3.7 mBq L−1 to 1,481 mBq L−1 and the 210Po activity ranged from 0.25 mBq L−1 to 555 mBq L−1. Of the select wells tested, 27% for 210Pb and 19% for 210Po were above the proposed maximum contamination limits for these radionuclides, which are set at 37 mBq L−1 and 26 mBq L−1, respectively. From a public health perspective this is a concern, since the drinking water screening levels for gross alpha is at 555 mBq L−1 and gross beta is at 1,850 mBq L−1. At such high screening levels 210Pb and 210Po will not be captured, and this situation was found in several of the wells studied. The occurrence of 210Pb and 210Po are not correlated within the sources, however; the polonium concentrations were always lower than the lead concentrations. Activities of 210Pb measured from wells two years apart clearly demonstrated the continuous flux of groundwater within aquifers.