The cost of the Oroville Dam spillway failure last February has risen to $870 million, according to a new tally released Friday by the Department of Water Resources that includes $210 million of work done by agency staff and consultants.
The department said in October that the cost of repairs by construction contractor Kiewitt would hit $500 million, but that estimate did not include the agency’s internal costs.
Heavy rains last year caused dam operators to release 55,000 cubic feet of water per second down the spillway, triggering the disintegration of the spillway and the evacuation of 188,000 nearby residents. An independent investigation found that the 1960s-era spillway had numerous defects, such as thin concrete, poor anchors to the underlying rock and the fact that it was set on weak rock.
Originally, the department estimated that the Kiewitt work would cost $275 million, but that was before greater damage was found in the foundation of the spillway. The initial design called for about 485,000 cubic yards of concrete, but as excavation of the loose rock proceeded, that was increased to 870,000 cubic yards.
The department said that it had spent $160 million responding to the crisis in the months after the damage. And it is spending an additional $210 million for debris removal, power line replacement, staff time and technical consultants, spokeswoman Erin Mellon said.
The Federal Emergency Management Agency is expected to cover 75% of the $870 million, with State Water Project agencies paying the rest, she said. So far, FEMA has reimbursed the department for $87 million.
The new cost estimate includes work that will be done later this year to rebuild an upper section of the spillway, along with additional work to the emergency spillway that also failed last February when dam operators tried to use it instead of the damaged main spillway.
Mellon said that the department is evaluating possible fixes to some of Kiewitt’s work, but it would be done within the $500 million contract. Three of the 234 concrete slabs have surface imperfections that may require fixes later this year. The concrete did not cure properly, because an outage at the concrete plant caused delays that let hot winds dry the concrete too quickly, the department said.
The department also noted that water pooling on the hillside has led to seepage through the spillway walls, but those walls were planned to be replaced later this year. It also noted a small section of a new wall is 1% out of vertical alignment and its engineers are examining whether fixes will be needed.