Abstract: At approximately 12:30 p.m. on May 15, 2007, Employee #1 was working at a site near Spring Road and Route 94 in Spring Valley, CA. Also at the site were a coworker, who was a drill operator, and a foreman. All three employees were employed by a commercial contractor that specializes in street and traffic light installations in Southern California. Employee #1 was a locator, who walked on the ground surface to locate the underground directional drill head using a detector unit to track the horizontal and angle movement of the drill head. This information was communicated back to the coworker, who was the operator seated on the directional boring machine (a Vermeer Number D24x40 Horizontal Directional Drill). The horizontal directional drill was used to dig under cement, pavement, and earth to lay electrical lines for street and traffic lights. The head of the drill first made a path through the soil underneath the ground, until it arrived at its destination. A line was then pulled through it, so electrical lines could be installed to hookup traffic and signal lights for public streets and freeways. The front section of the horizontal directional boring machine was outfitted with a left and right anchor boring unit with stakes. The stakes were large auger units that tapped into the ground vertically to stabilize the machine when its drilling rods apparently ran horizontally, underneath the ground. The bolt holding the auger bit to the shaft on the main frame of the directional boring machine came off, and the coworker had to take it apart to get to the dislodged bolt. Apparently, the coworker tightened the bolt, got up on the directional boring machine, seated himself, and unsuccessfully attempted to line up the square piece fitting of the shaft over the top of the auger attachment. Employee #1 came over and used his left hand to try and line up the shaft, while the coworker manipulated the controls, in an attempt to attach the shaft to the auger bit. The shaft dropped on employee's #1 left thumb, causing the top one inch to be amputated. The foreman transported Employee #1 to U.S. HealthWorks First and later transported him to the Orthopedic Center in La Jolla. Employee #1 was hospitalized and required outpatient surgery the day after the accident. The Division was notified about the accident on May 18, 2007. During the initial investigation, Employee #1 had not yet returned to work, but the Division found he had returned to work during a subsequent visit to another of the employer's job sites on June 11, 2007.