An employee was operating an excavator to excavate coal combustion residual (CCR) from below ground to create a sump. The sump was being excavated to a lower elevation to allow water to be collected at the bottom and pumped into a ditch. The surface material the excavator was placed on set down vertically approximately 6 to 8 feet. The employee then jumped off the excavator and landed on the ground resulting in a fractured left tibia.