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The steel pipe that tunnel machine Bertha struck in December wasn’t just some scrap that a contractor forgot to remove in 2002 — but a crucial piece of equipment that engineers reused as recently as 2010, to learn how groundwater and construction affect each other.

The findings were shared with construction companies during the homestretch of the bidding competition to drill the world’s widest single-bore tunnel.

The pipe’s location and purpose are described in two documents the state Department of Transportation (DOT) provided to potential bidders, including Seattle Tunnel Partners (STP), which won the $1.44 billion Highway 99 tunnel contract.

Yet somehow, Bertha hit the pipe Dec. 3. Workers removed a 55-foot section that had been pushed upward, and the machine advanced for three more days, until the cutting teeth stopped grabbing soil. Operators turned off the tunnel machine to avoid damaging it.

The incident set off a round of finger-pointing between DOT and STP over who is to blame for leaving the 119-foot-long well casing buried near South Main Street. Transportation Secretary Lynn Peterson has told state lawmakers DOT had concerns about STP’s tunnel-machine operation since drilling began July 30.

Bertha is now entering its eighth week stranded. Workers have been cleaning and inspecting the rotary cutting face, which is flooded by groundwater, to learn whether steel fragments, a large rock, or other things are hindering the machine.

Officials say they don’t know when drilling will resume.

DOT waited until Jan. 3 to acknowledge that Bertha had struck its own research pipe, installed a dozen years ago, and spokesman Lars Erickson emphasized: “I don’t want people to say WSDOT didn’t know where its own pipe was, because it did.”

STP’s project director, Chris Dixon, responded: “If we had known the pipe was there, we would have removed it.”

The state is not disclosing an estimated cost of delay — which likely will be negotiated or litigated.

Highway 99 contract documents, released to The Seattle Times under a public-records request, show the pipe is discussed in two geotechnical reports. In addition, the state’s 2010 project requirements said it was the contractor’s responsibility to decommission groundwater monitoring wells after tunnel boring, “with WSDOT’s concurrence.”

Still, the pipe was overlooked in the early stages of construction.

“I really can’t say why this wasn’t discussed,” said Ron Paananen, who was DOT’s Highway 99 administrator in 2010. Linea Laird, who was then deputy administrator and later succeeded Paananen as administrator, said she doesn’t recall conversations about the pipe, but that sort of thing would have happened at a lower level.

Paananen added: “It’s not an unusual piece of equipment to be left in place, for a contractor to remove later.” Paananen is now Seattle manager for Parsons Brinckerhoff, longtime design consultant for the project.

Ironically, tests using this pipe helped yield information workers now need as they pump huge volumes of water away from the stalled machine.

Known as Test Well 2, the steel casing was installed in 2002 to study how pumping away groundwater to build a cut-and-cover tunnel along Elliott Bay — then the leading political option to replace the aging Alaskan Way Viaduct — might affect aquifers, buildings and the work itself.

The research was done by Seattle-based Shannon & Wilson, which knowingly left its pipe in place.

In 2009, Gov. Chris Gregoire chose a 1.7-mile, deep-bore tunnel to run mostly under downtown. Three new pumping wells were created to reflect the new alignment, but officials had moved the south end toward the waterfront, a block farther from fragile Pioneer Square brick buildings.

So waterfront pumpsite TW-2 was still in position to be reused, from March 20-23, 2010.

Crews simultaneously pumped from another well in Sodo, to see how that would affect a common aquifer.

Showing how large the issue loomed, the 2010 study included 52 wells where groundwater levels or pressures were measured.

After the water studies, steel caps were placed at street level to protect the tops of the test sites, most of them PVC tubes. (PVC fragments were found a week ago in the cutting face; a plastic sampling well had been installed near the steel pipe.)

The study didn’t specifically address decommissioning the steel pipe.

STP’s Dixon last month said he initially thought the pipe wasn’t especially deep, and that Ecology Department rules required such wells to be removed.

STP didn’t respond to an interview request last week.

The contractors’ understanding of the groundwater levels, based partly on these pipe tests, led STP to set concrete slabs above the tunnel’s far south end, to keep the tube from floating upward.

It’s no surprise groundwater flooded the cutting face, so much that STP is using 10 pumps to lower the levels enough so workers can inspect the top half of the 57-foot diameter rotary cutter.

If luck had prevailed, perhaps construction workers still would have found the well before Bertha did.

“We also now have the piece of the [steel] casing that’s from the very top, and there’s evidence that that was driven over repeatedly,” after control of the waterfront site was handed to STP, Todd Trepanier, DOT’s current tunnel administrator, told a state Senate committee Jan. 16.

At the same time it blames STP, the state also contends that the pipe alone doesn’t explain the tunneling delay.

Peterson, the transportation secretary, said in a letter to STP’s Dixon on Monday: “As to the cause of the current tunneling stoppage, we have all agreed that it is highly unlikely that the well casing is the only issue facing the machine.”

If her argument is true, the team confronts deeper troubles than unraveling some mangled steel.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom