AUGUSTA – Cranes, earth-moving equipment and tons of construction materials are already on the site as a formal groundbreaking takes place today for MaineGeneral Medical Center’s new $312 million, 640,000-square-foot regional hospital.

It will be built on a 40-acre site just off Interstate 95 in a rural area of north Augusta, which will ease access for patients who now use downtown hospitals in the capital city and Waterville, about 20 miles away. The new hospital is being funded entirely with private sources, mostly 30-year bonds issued by MaineGeneral.

Funding also includes a $35 million grant from the Harold Alfond Foundation, named for the shoe company founder and philanthropist, which also provided major funding for the four-year-old Harold Alfond Center for Cancer Care that’s next to the new hospital’s site.

MaineGeneral says the project, due for completion in the summer of 2014, will be a huge economic boost to the region. At the peak of construction, it’s expected to employ 630 workers, bringing $266 million into the state in direct and indirect spending, according to the Maine Development Foundation.

Chuck Hays, president and chief executive officer of MaineGeneral Medical Center, said it became clear a few years ago that “we had to rethink our model and regionalize our approach, and make it more efficient.”

The new regional medical center will not only improve efficiency in buying and delivering services, but also in attracting physicians, he said.

Once it’s built, the hospital that is already the area’s largest employer will have more than 3,800 employees.

With an annual payroll exceeding $136 million, it’s estimated that $29 million will be spent yearly with central Maine businesses.

MaineGeneral will convert its Thayer campus in Waterville from an inpatient facility to an outpatient facility, and it will close both the downtown Augusta location and its Seton campus in Waterville, which currently provides rehabilitation and other services and offices.

MaineGeneral is working with officials in the two cities to find new users for the properties.