South Carolina Electric & Gas Co, said today it has completed a six-foot-thick foundation for a second reactor at the V.C. Summer Nuclear Station in Fairfield County.

“This major milestone is the first new construction nuclear concrete to be poured in the U.S. in three decades,” SCE&G said in a statement.

The “nuclear island basemat” provides a foundation for the containment and auxiliary buildings. It required enough concrete to cover an area about 250 feet long and 160 feet at its widest section.

It maked the end of a continuous pour that lasted slightly more than two days. The projected was completed at about 10 a.m.

About 1,550 workers are involved in constructing two reactors at V.C. Summer near Jenkinsville, north of Columbia. The project will peak at about 3,000 workers over the next three to four years.

The two 1,117-megawatt units will cost about $10 billion and create 600 to 800 permanent jobs. They are expected to start generating electricity in 2017 and 2018, respectively.