Use of borehole scintillator probe total-field gamma scans in radioactive waste investigations, Hanford Site, Washington

Radioactive wastes have been stored in underground tanks or discharged to the unsaturated zone since the startup of Hanford chemical separation facilities in 1945. NaI (Tl) scintillator probe scans of approx. 1000 boreholes are routinely taken to measure the total-field gamma radiation intensity at waste storage and waste disposal sites. Conclusions are: (1) most radioactive contaminants are retained near the points of discharge; (2) downward redistribution essentially stops shortly after discharge has ceased; (3) radiation intensity decreases rapidly with depth due to selective sorption of radionuclides on the sediments; and (4) radiation intensity beneath retired facilities decreases with time due to radionuclide decay