THE EE WAS OPERATING HAUL TRUCK HT-801 ON SEPTEMBER 14. DURING THE SHIFT HE FELT SEVERAL BUMPS IN THE ROAD CAUSING A TINGLE IN THE LOWER BACK. HE DID NOT REPORT THIS AT THIS TIME. HE RETURNED TO WORK ON SEPT 15, CONTINUING TO DRIVE THE HAULTRUCK WHEN AT APPROX. 11:30 A.M. HE STOPPED THE TRUCK AND NOTIFIED HIS SUPERVISOR OF LOWER BACK PAIN.