George Mahfouz joined the Manhattan Project in 1943 when he was offered a job at the Houdaille-Hershey nickel plant in Decatur, Illinois. Mahfouz helped produce the nickel barrier material for the massive K-25 gaseous diffusion plant in Oak Ridge. When District officials decided on a different barrier material and the plant closed, Mahfouz left Decatur and joined the Monsanto Chemical Company in Dayton, Ohio, which the MED tasked with separating and purifying polonium-210 to be used as the initiator for the plutonium bomb.
Mahfouz joined the Process Engineering Group at Runnymede Playhouse, a leisure facility that was converted into a top-secret laboratory in early 1944. After the war, Mahfouz was tasked with cleaning up the Playhouse, which had become so radioactive that it had to be dismantled and buried in 1950. Mahfouz spent the rest of his career with Monsanto at Mound Laboratories in Miamisburg, Ohio.