An anonymous reader writes: A few weeks ago we discussed news that a tunnel boring machine measuring 57.5 feet in diameter was halted underneath Seattle after running into a mysterious object. Project engineers have now figured out what the object is: an 8-inch-diameter pipe. In 2002, researchers for another project — the replacement of the Alaskan Way viaduct — drilled down into the ground to take water samples. They used the 115-ft-long pipe as a well casing. As it turns out, this well site was listed in the contract specifications given to all bidders for the tunnel's construction. In addition, the crew manning the machine noticed that it was chewing up pieces of metal, and they removed part of the pipe and kept going. Only later did they realize that significant damage had been done to the machine's cutting face. Officials aren't sure how long repairs will take, or how much they will cost.