An employee was installing a grounding rod next to an electrical panel using an impact tool. He was standing at the edge of a trench which was approximately 2 feet deep. It had rained the previous day so the ground was damp and loose. The tool was placed on top of the grounding rod and it covered approximately 6 inches of the top of the rod. The employee would lift up the tool without exposing the top of the rod and then using a downward force, drive the rod into the ground. One of the times, after lifting up the tool, the ground underneath the employee shifted causing him to lift the tool off the rod as he pulled up on the tool. When the employee began the downward force with the tool, the ground under him gave way causing him to fall forward onto the grounding rod, striking part of his face and his eye.