The incident happened at approximately 11:30 a.m. Thursday at a pumping station at 100 Team Road in Aston, Pa.
Authorities tell Action News four Southwest Delaware County Municipal Authority employees were working on a wet well when at least two fell in.
One employee has died and another was treated and released from Crozer Chester Medical Center.
The two other employees were not injured.
"No words can express the sadness that comes when such a tragic event occurs. On behalf of everyone at Southwest, my deepest sympathies go out to the families and friends of Larry Fisher, a 13 year employee at the Authority. They have suffered a devastating loss," Operations Manager Fred Tasker said.
The incident is currently under investigation by the Aston Township Police Department. Find out about Breaking News as it happens. Sign up for 6abc.com Breaking News Alerts.