EE, PRIOR TO STARTING HIS WORKSHIFT, WENT TO THE PIT TO DUMP A LOAD OF TRASH. HE BACKED HIS PERSONAL TRUCK UP TO THE EDGE OF THE DRAGLINE BENCH CLOSE TO WHERE TRACTORS WERE STRIPPING. HE GOT INTO THE BACK OF HIS TRUCK AND WHEN HE THREW AN OLD ANTENNAE TOWER OUT, HE LOST HIS BALANCE AND FELL ABOUT 15-20'TO THE ROCKS BELOW. THE TAIL GATE OF THE PICK UP WAS DOWN & HANGING OVER VOID.