The city of Columbus' most expensive public works project just got more expensive.
Construction delays have pushed back the completion of the city's underground tunnel.
The tunnel is designed to prevent storm water overflows that result in raw sewage dumped into the Scioto River.
Since 2011, Columbus taxpayers have paid higher water and sewer rates to help fund this drilling project.
The massive drill is now 170 feet below Whittier street in the Brewery District.
But construction delays have driven up the cost and the city isn't sure just how much more it will take to get the job done.
A 95 ton drill is chewing through rock under the city of Columbus at a cost of $341 million dollars.
But two miles into the 4 mile project, problems arose when engineers, "started noticing a year ago that progress in the tunnel wasn't as we hoped," said George Zonders, spokesperson for the Department of Public Utilities for the City of Columbus.
The city says progress began to slow when the giant drill encountered too much water.
Then the rocks it was tearing off were coming in chunks bigger than the equipment could crush causing the drill to stop.
"When you get 20 stories underground you're going to find things that are different than what you anticipated," said Zonders.
He says the project is now a year- and- a-half behind schedule.
The question is: Will the delay cost taxpayers? And how much?
The answer is, no one really knows.
"It's really going to depend on when we get to the end of the project and we look back what have we incurred what do we need to do. In all likelihood it will cost more than we originally projected," he says.
The tunnel is designed to stop a persistent problem downtown.
When heavy rains fall, the downtown combined storm water/sewer system gets overwhelmed.
As a result, raw sewage is dumped into the Scioto River. It happens 38 times a year.
The tunnel is designed to prevent that by capturing billions of gallons of storm water and sewage and pump it to the waste water treatment plant before sending to the river.
But that won't happen until later than expected, and at a higher cost.
For now, the city says it's goal is simple, "The main goal is to get the thing finished," said Zonders.
The city has a contingency fund built into the contract for cost overruns but says it isn't sure if it will cover the delays.