Castle Medical Center plans to buy Hawaii Pacific University’s sprawling Windward Oahu campus to expand its health-care offerings.

Kathryn Raethel, president and CEO of the Kailua hospital, said the medical center has executed a purchase agreement and is embarking on a four-month due diligence phase before finalizing a sale for the 130-acre site at the base of the Pali. She declined to disclose terms of the sale at this time.

“We have a purchase and sale agreement, we have an intent to buy the property, we have an intent to expand our footprint in Windward Oahu using that property,” Raethel said in an interview today. “Certainly, as I look at what potential there is for that land, I think this is one of the best possible options for Windward Oahu — to have a better established and more accessible healthcare campus for the Windward community.”

The hospital operates a 160-bed facility with 1,000 employees and 300 physicians on Ulukahiki Street. In calendar year 2015, Castle reported more than 8,500 inpatient discharges and 64,000 outpatient visits, while its emergency department received 34,500 visits.

Raethel said the hospital, which is owned and operated by Adventist Health, a Seventh-day Adventist health care system, plans to retain its existing site, located about 2 miles away from HPU’s campus.

“Castle has been successful for 53 years. We’re sitting on a 10-care campus and … when you’re building a new hospital today, you need probably closer to 40 acres, so we’re very land-locked here at Castle,” Raethel said. “We’ve been thinking about how we can approach that problem, and then this opportunity just presented itself to us and it just seemed like a really good future solution for that problem.”

She said the hospital expects to lease back the site to HPU for three to five years or more, which will give Castle time to complete master planning for the property.

School officials told the Honolulu Star-Advertiser in April that the decision to pare down to one campus was the result of a years-long planning process, adding that it has been costly to run two campuses.

“The Hawaii Loa campus is more than a piece of land,” HPU President Geoffrey Bannister said in a statement. “This campus has been a place of learning for over 40 years, and we are pleased to have identified a buyer that will continue to use it in providing for the needs of our community.”