The cost of repairing the landslide at Riverfront Park has increased by $35,000.

The Board of Mayor and Aldermen Wednesday approved a change order to its contract with Central Asphalt of Vicksburg totaling $35,850 to remove pieces of concrete found recently during excavations at the site of the slide area on the south end of the park. The extra cost will be split between the city and county, which jointly operate and maintain the park.

The discovery is the second problem affecting the project. Workers in January uncovered oil from an old storage site on the property, forcing the project to shut down until the oil could be removed from a shallow 8-foot diameter container, Brian Robbins with Stantec, the project engineer said. “It was not as bad as we thought,” he added.

Robbins said the concrete pieces are adjacent to the site where the oil was found.

“There’s some old slabs and concrete retaining walls that were unearthed as we excavated,” he said. “They need to be removed because it’s a safety hazard, and it’s a threat to the stability of the site as well.”

Robbins said he did not know what the slabs and walls of varying thickness were used for.

“It would be almost impossible to tell, unless you find somebody who has all the history of it,” he said. “It’s just a bunch of old stuff down there. Those are what we have to remove to get below grades so we can get our slope back in there.

“We’re going to get it all chipped off and knocked off and excavated and hauled away a couple of feet below grade,” he said. “So when we get the dirt back over it we can grass it.”

Robbins said the dirt removed from the area where the concrete was found will be returned to the site.

City and county officials closed Riverfront Park for 90 days in December to let Central Asphalt repair the slide area on the south end of the park and resurface the play areas. The board extended the work period by an additional 60 days after the oil was found.

A section of the bluff on the south end of the park began slowly sliding off the bank in April 2015, taking part of the park’s perimeter fence and walking trail, and threatening one play area, part of which sits on the slide.

The city and county boards have each contributed $150,000 to the project, which was delayed while the Mississippi River level fell so the repairs could be made.

The city and county also contributed the extra money to make up the $24,374 difference between the bid and the original amount set aside for the project.

To fix the slide, a contractor will have to excavate topsoil along the top bank of the river — a project that will require removing some playground equipment to provide enough room to make the repairs, which involves dirt work and rehabilitating underground drain pipes that were part of the cause of the slide.