The full report with the longer message (linked elsewhere in this thread; page 214 or F-125) explicitly notes that the 10,000 year point is when it matches the

The full report with the longer message (linked elsewhere in this thread; page 214 or F-125) explicitly notes that the 10,000 year point is when it matches the ore: > Radioactivity declines exponentially with time. By 10,000 years after the waste was buried here, the waste will be no more hazardous than the ore from which the radioactive material was taken [see 50 FR 38071a].