This afternoon, we were dispatched for a possible chemical leak at the Mid Mon Valley Sewage Authority & Treatment Plant. Chief 17 arrived on scene and found a very strong smell of Chlorine in the treatment facility. Squad 17 arrived on scene and sent in masked personnel to investigate. It was found that a valve was opened and chlorine fumes was filling the facility. Firefighters closed the valve and then set up a PPV fan to ventilate the structure. After roughly 20 minutes had passed, crews went back in with both a fire department detector as well as a detector from the sewage authority and found the room was safely ventilated. The scene was turned back over to the plant operator & all units cleared without incident.