Charleston's drainage project along Septima P. Clark Parkway is actually $43 million over budget, not $30 million as City Council was told last week. 

The project administrator, outside engineering firm Davis & Floyd, identified the higher costs over the past week while preparing a budget breakdown for Tuesday's special meeting with council. 

The cost estimates for the project's last two phases increased by $7 million in the last week, and the price was adjusted to include a $6 million cost for work that's already been completed and paid for by the Charleston Water System.

That puts the total project cost at $197 million. When it was designed in 2009, it was expected to cost $154 million.

Council learned last week that the original budget grossly underestimated what the final phases would cost, and that the timeline was off by about four years. The meeting on Tuesday was scheduled so Davis & Floyd could explain why.

The project, also called the Spring-Fishburne Drainage Improvement Project, covers two drainage basins on the western portion of the peninsula, and is meant to fix the flooding problems along the six-lane parkway, also known as the Crosstown, that runs through them.  

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 during a high tide.

The firm's chief engineering officer, Michael Horton, said the project was originally designed when it was expected to be fully funded by the federal government and completed by one contractor within a three-year period.

Those plans didn't pan out, and the project was ultimately split into five phases to be done from 2012-20. Horton told council that the cost estimate wasn't adjusted to account for inflation, or possible construction cost increases, or anything else that might drive up the cost over time. The budget stayed the same, and for a while, that didn't seem to be a problem, Horton said.

There weren't any unexpected cost increases during the past three phases, and in fact some ended up costing a bit less than expected. So there wasn't any reason to anticipate higher costs for the other phases, he said.

"There was not a call or cause for concern that we needed to be tight going forward," he said. "We didn’t see there was a need to look at things from a cost standpoint."

Then, earlier this year, the Public Service Department requested a full cost estimate for the fourth phase before the city put the contract out to bid. That's when the firm discovered all the additional costs, which were reported to the department and Mayor John Tecklenburg in October, according to Horton and the mayor.

Some, but not all, of those added costs were explained to council in a balance sheet. They included $10.5 million for engineering, $10.3 million for higher construction costs and $18.6 million in design improvements.

Councilman Keith Waring said he still didn't understand why those costs weren't accounted for to begin with, and why most on council only found out about them last week. 

"It has to be a different reporting process going forward," he said. "We were just sorely lacking in information on this project."

Right now, the contract for the next phase is on hold pending more information. 

The first two phases have been completed, and the third is expected to wrap up in 2020. But none of them will have any substantial impact on the flooding until the fourth phase is done, which includes building the outfall to the Ashley River.

"We, in fact, have pipes to nowhere in the ground," Horton said.

Tecklenburg said the city can cover the $31 million higher cost for phase four, but it's unclear at this point where the extra $11 million will come from to complete phase five. 

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.