The Department of Ecology now says an unusual reading of radioactivity at Tank C-101 may have been in a transfer system.

Wednesday night workers were evacuated as a precaution after the unusual reading.  Workers left the C Tank farm, which has 16 underground tanks, around 9:35 p.m.

The DOE says the leak may have occurred near what is called sluice box, which contains equipment used to help remove waste. The equipment is used to spray contaminated liquid onto the waste so it's easier to remove. By using already contaminated liquid instead of water, less new waste is created.

Crews found no evidence of a traditional leak, but still found higher-than-normal radiation levels this morning near the sluice box.

No injuries or public threats were recorded. Hanford was on an "alert" -- the lowest form of activation issued by the DOE -- from 9:35 p.m. until just after 5 a.m. Thursday.

The C-tank farm is currently being worked on, as crews are attempting to have all of the single-shell tanks emptied of waste by September 2014.

The C-farm is the only collection of single-shell tanks currently being worked on. Single shell tanks are considered the most volatile and likely to leak and waste is being pumped into newer double-shell tanks until the completion of the vit plant where the waste will be treated.