STP has received proposals from various firms to design the shaft, which will be 100ft deep by 80ft wide.

"While STP has shared their preferred method for accessing the seal system, they are waiting until after their meeting with Hitachi to provide WSDOT with an official plan," WSDOT said in a release. "Because this is a design-build contract, STP and their machine manufacturer are responsible for developing and implementing the plan to fix the machine and resume tunnelling."

STP has not yet fully determined the cause of the seal problems, though anticipates the plan for repair to be finalized by end of February.

"We can’t forecast what the delay might be," said Chris Dixon, project manager for STP. "What we really need to do is determine what we need to do at this juncture and how soon we can resume tunnelling."

The 57.5ft diameter TBM stopped working on December 6, 2013. WSDOT and STP have identified two contributing factors: a clogged cutterhead and high-temperature readings indicating "there were other factors to explore." Tunnel workers performed 158 hours of hyperbaric inspections in January, the cutterhead clogged with dirt and other material.

After the cutterhead was unclogged, STP moved the machine forward an additional 2ft installed one ring of lining. On Jan. 28 and 29, higher-than-normal heat sensor readings appeared like they did in December. In the course of investigating the temperature readings, STP discovered damage to the seal system that protects the tunneling machine’s main bearing.