The accident Thursday morning in Gatlinburg happened at the same site where two workers were killed last year.
Gatlinburg officials said in a news release that the trench gave way as workers demolished a concrete basin that had collapsed last April. The accident last April killed two plant operators and dumped more than a million gallons of untreated sewage into the Little Pigeon River in the Smoky Mountains resort town.
State investigators were dispatched Thursday from Kingsport. Results of their investigation are likely in six to eight weeks, a spokesman in Nashville said.
City officials said they would release details later Thursday.
