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Data from a radioactive waste disposal area at Oak Ridge National Laboratory suggest that releases depend on site hydrology and waste containment. Loss of packaging integrity has apparently caused episodic increases in 90Sr source strength, followed by gradual reduction as runoff carries contaminants away. Most flow and transport occurs during January–April storms in response to site hydrology. Diversion of runoff from undisturbed areas upstream of the waste site (1983) reduced flow through the site by more than 65% and annual 90Sr release by more than 45%. However, between 1983 and 1994, increases in 90Sr source strength have partially offset the diversion effectiveness. Selective source control in 1996 further reduced annual 90Sr releases by more than 30% in the first two years, compared with pre-treatment conditions. The effectiveness of the grouting treatment should increase over the next 5–10 years, if new 90Sr sources are insignificant. [ABSTRACT FROM AUTHOR]