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Construction on the Spring-Fishburne drainage system is underway between the Ashley River bridges on Wednesday, Dec. 5, 2018. Lauren Petracca/Staff

Charleston must spend $30 million more to complete the massive, deep-tunnel drainage system along the Septima P. Clark Parkway and it'll take another six years for the work to be done.

Original plans set the budget at $154 million, with a completion date of 2020. Now it's not expected to be done until at least 2024 and run about 20 percent more expensive than anticipated.

The peninsular parkway, also known as the Crosstown, connects West Ashley to the downtown medical district, Interstate 26 and the Arthur Ravenel Jr. Bridge. For about as long as it's existed, the six-lane road has flooded in almost every major storm, often shutting down traffic in one of the busiest thoroughfares in the Charleston region.

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The crosstown drainage project is millions over budget and projected to take four more years than expected. Flooding on the Septima P. Clark Parkway forced morning rush hour traffic to a stop on Friday, July 20, 2018. File/Matthew Fortner/Staff

In 2009, under then-Mayor Joe Riley, the city embarked on a plan to solve the problem, setting off the most ambitious and expensive drainage project in its history. 

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Crosstown drainage area

Staff/File

When completed, it will send stormwater to new 12-foot-diameter tunnels 140 feet underground. From there, the water will go to a new pumping station where three pumps capable of moving 120,000 gallons per minute will empty the water into the Ashley River, even when it's high tide.

But city officials now say that plan vastly underestimated how much the last phases of the project would cost. The fourth phase, which includes building the outfall to the Ashley River, will cost $24 million more than expected.

The fifth and final phase of installing the three large pumps in between the Ashley River bridges will cost about $6 million more than was budgeted. 

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Constuction on the Spring-Fishburne deep tunnel system is underway at the crosstown on Wednesday, Dec. 5, 2018. Lauren Petracca/Staff

All of this was revealed to City Council for the first time Tuesday when the Ways & Means Committee was asked to approve the $52 million contract with Conti Construction Co. to do the fourth phase, plus another $6.8 million for engineering.

The extra $24 million was covered by a special tax-increment financing district and the city's drainage fund.

Several council members began asking questions about where the project stood, and city staff struggled to explain.

When Councilman William Dudley Gregorie asked what led to the increased cost and timeline, Chief Financial Officer Amy Wharton said the project manager, Davis & Floyd, was going to work on answering that.

"Council's just finding this out?" Gregorie said. Silence followed.

Other council members were just as concerned. 

"This should have been before us a long time before now," Councilman Bill Moody said. "I don’t want this to be Charleston’s V.C. Summer nuclear plant."

That was a reference to the failed nuclear site in Fairfield pegged at a $9 billion debacle.

Councilman Keith Waring, who chairs the Public Service Committee, said he had no idea why the fourth phase would cost $24 million more than expected.

"I couldn't tell you that answer to save my life. We need to know that," he said. 

The next major drainage project on the city's horizon, Calhoun-West, is expected to cost even more than the one on the Crosstown. Councilman Mike Seekings said that's why council needs a full understanding of the budget and what's delaying the project.

"In some ways it’s a test case, and this test case is somewhat floundering," he said. "We need to get it in line so we can get other projects going and not go broke doing it."

Council deferred all financial decisions about the project and scheduled a special meeting to learn more about it on Dec. 18.

Mayor John Tecklenburg said the prices could escalate further if a decision isn't reached after that meeting.

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Floodwater inundates a home near President Street and Septima P. Clark Parkway. The crosstown drainage project is over-budget by millions and four years behind schedule. Matthew Fortner/Staff

City spokesman Jack O'Toole told The Post and Courier on Wednesday the city learned the fourth phase would cost much more when it put that portion of the project out to bid. The lowest bidders estimated about the same price tag for the work, which indicated that, for whatever reason, the original budget underestimated what the true cost would be.

"We have and will continue to look into why that would be, whether that involves construction costs, inflation or other items," he said. "We don’t know whether there were pieces that were left out of the original estimates."

The first three phases of the project remained on budget, so it's not that overspending has driven up the project's price, he said. 

Different contractors have been hired for each phase of the project and that approach has likely stretched out the timeline, he added. 

Phasing is a standard approach for the city's capital projects, he said, and it was necessary in this case because different sources of funding from the state and federal governments paid for certain things. 

He said the city expects to pay the extra $6 million to complete the final phase of the project.

Reach Abigail Darlington at 843-937-5906 and follow her on Twitter @A_Big_Gail.

Abigail Darlington is a local government reporter focusing primarily on the City of Charleston. She previously covered local arts & entertainment, technology, innovation, tourism and retail for the Post and Courier.