About 50 people have been treated for breathing problems following a leak from a chemical company in Jefferson County. The chlorine leak from the DPC Enterprises plant in the Festus-Crystal City area of the County occurred around 9:30 this morning. The leaking valve was finally shut off just before 12:30 this afternoon. Authorities say a hose from a railway tanker ruptured, causing the problem. The leak forced the evacuation of several hundred families in the area. About 30 people were sent to the hospital. The cause of the leak is under investigation.