WHILE OPERATING EXCAVATOR W/ROCK BUCKET, A DUMP TRK OWNED BY H20 ENVIRONMENTAL WAS BACKING UO NEXT TO THE EXCAVATOR THE TAILGATE SWUNG OPEN ONTHE DUMP TRK PINNED EE'S LEG INSIDE THE CAB OF T HE EXCAVATOR. DURING THE CONTINUING BACK OF THE DUMP TRK EE'S LEG RECD A BIG GASH/WOUND HE WAS TAKEN TO MH VIEW HOSPITAL