The reopening of the portion of West River Parkway in Minneapolis that was closed by a mudslide last year won’t happen until December at the earliest.

That’s the new schedule announced Friday by Minneapolis park staff following the latest setback in a complicated, nearly $4 million construction project that is attempting to install four walls to stabilize the steep slope above the parkway.

The contractor has been using a mobile drill on a temporary bench of soil to install pilings before pouring one of the upper walls. But water seeping from the limestone saturated the soil, causing it to slump and sending more soil onto the parkway. That forced the contractor to pull back the machine.

The Sept. 16 incident set back a schedule already lagging behind the planned October completion date for the project, according to Cliff Swenson, director of design and project management for the Minneapolis Park and Recreation Board. He said the new completion date tentatively is the end of the year “if everything goes OK.”

The moisture, steep slope and complex geology caused both extensive testing and a lengthy construction schedule. Contractor Veit & Co. is drilling now on a different portion of the bench and will use additional techniques to try to hold a rebuilt portion of the bench in place, Swenson said.

The parkway has been closed since heavy rain caused about 4,000 cubic yards of soil and debris to tumble onto the parkway in June, 2014. The section of parkway across from the University of Minnesota had been used by about 6,000 motor vehicles a day.

“It’s an emergency repair and a difficult site,” Swenson said. “We want to project completed correctly.”