The Grant County Public Utility District says pressure from the water behind Wanapum Dam may have contributed to the big crack that has disrupted operations at the dam.
The utility said Wednesday that it has ruled out four other causes for the crack. Ruled out were seismic activity, foundation settlement, operation of spillway gates, and explosions at the nearby Yakima Training Center operated by the U.S. Army.
The 65-foot-long fracture was detected by divers on Feb. 27, three days after a dam worker noticed that the top of a spillway pier had shifted slightly. When the reservoir behind the dam was drawn down, the pressure on the spillway was reduced and the fracture closed, stabilizing the spillway pier.