BELLEVILLE — Developers are three weeks into the building of Kimball Plaza at Bicentennial Park and they've run into an unexpected problem: muck and debris in the area planned for the parking lot.

"They uncovered an old creek when they were digging out there and it's got a certain amount of soil underneath it," Mayor Mark Eckert said Friday. "There's going to be some additional costs to dredge it out."

Eckert did not have an estimate of the cost of the extra work on Friday, but he said Mettler Development will have a number by Monday.

The mayor plans to ask the Streets and Grades Committee to approve the extra work at a regularly scheduled meeting at 6 p.m. Monday.

The issue is also on the agenda of the City Council meeting scheduled for 7 p.m. in the City Council Chambers at Belleville City Hall, 101 S. Illinois St.

Eckert said he included the issue on the agendas after hearing from developers on Wednesday so the project won't be delayed.

Meanwhile, developers continue to assess how deep and widespread the muck goes and its impact on the project design, Eckert said.

"Anytime you do a project you always run the risk of running into something unexpected," Eckert said. "There's always those unforeseen things no matter how hard you try to forecast and plan."

Ward 7 Alderwoman Lillian Schneider said this is just the beginning of unexpected costs tied to this project.

"This is just going to lead into a big money pit, I already know," Schneider said.

In July, Schneider and other aldermen voted against building Bicentennial Park. They said city officials did not explain how they plan to develop the park in the long term and how the city would pay for the project.

Schneider said she was on the project grounds last week and saw tires and wheels in the muck, and developers told her the unstable ground was probably 15 feet deep.

Schneider also said aldermen should be informed immediately of such issues and not have to wait for a City Council agenda to learn the project calls for additional costs.

Aldermen do not have enough time between getting the agenda on Friday and voting on Monday to make an informed decision on whether to approve additional funds, Schneider said.

"They found a serious problem and they should have sent a memo out," she said. "They expect you to do this overnight and it's wrong."

Ward 5 Alderman Joseph Hayden said in email, "It is very disturbing that agenda has a motion to approve extra work at Kimball Plaza, and no detail in our council packet!"

Eckert said city officials aren't trying to keep information from aldermen and developers simply needed time to gather information about the issue.

"By Monday, we will have the facts," Eckert said. "It was important to get on the agenda so we don't have to wait another two weeks or so."

Eckert said the project is on time for its December completion date.

Work on the park began in August after the City Council approved an $845,083 contract with Mettler for the first two phases of the project.

The Mettler contract will be paid for in part by tax increment financing funds and what's left of a $400,000 family trust from the Kimballs.

As part of the agreement with the Kimballs, 2 acres of the park will be dedicated as Kimball Plaza to honor the late Dorothy May Kimball and Edgar Rollins Kimball. The plaza must be done by Dec. 15.

The first phase includes the plaza and a parking lot, gazebo, sculpture, nature garden and trails.

The park will be open to the public in spring 2013 after restrooms and lighting are installed in the second phase.

Contact reporter Jacqueline Lee at jlee@bnd.com or 239-2655. Follow her on Twitter at twitter.com/BNDBelleville.