St. Tammany Parish has reached an agreement in principle to sell part of the Southeast Louisiana Hospital campus near Mandeville to Northlake Behavioral Health Systems for $6.7 million, officials announced Friday.

The sale, which is expected to be completed early next year, will turn over 35 acres and 13 buildings to the private company, which already operates a mental and behavioral health hospital at the site.

The purchase will allow the company to invest in improving the facility to expand its offerings, said Richard Kramer, Northlake’s chief executive officer.

“There are a couple of additional units we intend to open” after the purchase, he said. They include a crisis center and more space to treat people who pose an immediate threat to themselves or others.

The hospital now houses about 130 patients per day and offers some outpatient services, he said. It employs about 340 people at the site.

“It’s a good deal for us because we can continue building what we started at the campus,” Kramer said.

The sale includes 13 buildings with about 230,000 square feet of space. The land and buildings were appraised at $6.7 million, the purchase price, officials said.

The campus is zoned for health care, and by purchasing the property, Northlake signifies its commitment to remaining there long term, Kramer said.

Although the hospital will be private, an agreement with the state requires it to treat patients who can’t afford to pay for services, Kramer said. That agreement runs for two more years, and he said he expects it will be renewed.

The sale is another step in Parish President Pat Brister’s effort to make the site a “one-stop shop” for those who need mental or behavioral health services. The parish plans to renovate 62,000 square feet of vacant buildings, known as the “quad complex,” into a facility offering an array of addiction and mental health treatment services.

Those plans are still in the early stages, but Brister said the facility, which she calls “Safe Haven,” is beginning to take shape.

Friday’s announcement marks the continuing transition of the site from state control to operation by a coalition of public and private partners led by parish authorities.

The parish finalized its $15.4 million purchase of 293-acre Southeast Louisiana Hospital — which the state had announced plans to privatize — in March.

Not all of the site will be used for mental health treatment. Some will be used to build a connector road from U.S. 190 to La. 1088, some will be put into the parish’s wetlands mitigation bank and about 100 acres will go to Pelican Park for the public recreation complex’s expansion.

But selling part of the campus to Northlake is key, Brister said.

“This hospital is, and will continue to be, a model of a private-public partnership,” she said.

Follow Faimon A. Roberts III on Twitter, @faimon.