Work on the $46.6 million Lake Hefner Water Treatment Plant Expansion began in February 2011. The project involved the construction of two 130 foot diameter clarifiers, each capable of processing 25 million gallons of water daily, a recarbonation basin, a 24,700 square foot filter building housing 12 new filters, a 3,500 square foot filter backwash building, a 1,200 square foot carbon dioxide building, and a 2,800 square foot carbon dioxide storage facility. The project was completed in July 2013. The existing plant remained in service during the construction. The completed expansion project, which contained 22,000 cubic yards of structural concrete, increased the plant’s processing capacity from 75 million gallons to 100 million gallons daily.