(AP) — The Air Force is raising its cost estimate to $420 million to repair and replace structures damaged at Nebraska’s Offutt Air Force Base following severe flooding that inundated buildings with water.

Air Force official John Henderson tells the Omaha World-Herald that about 60 structures must be demolished after Missouri River flooding overwhelmed the air base in March. The buildings were destroyed by floodwaters up to 9 feet (2.7 meters) high, as well as a toxic sludge left behind when the waters receded.

The latest estimate is $70 million more than the initial estimate issued last month as part of a $4.9 billion federal funding request for disaster relief.

Henderson says $300 million would be designated to design and build new structures, while $120 million will go toward cleanup and repairs.