Castle Medical Center is proposing to turn Hawaii Pacific University’s sprawling Windward location into a medical campus with a cancer center, outpatient services and physician office buildings surrounding a new 160-bed hospital.

Adventist Health Castle, which operates the Kailua hospital, acquired the 132-acre campus in 2016 to expand health care services in Windward Oahu and is planning to repurpose or replace HPU’s existing structures sometime after 2021. That is the maximum time the school can extend an existing lease agreement, the company said in an environmental impact statement preparation notice that was released Friday by the state Department of Land and Natural Resources. The project will be built in three phases over 15 to 20 years.

The new hospital building will include a chapel, cafeteria, pharmacy and gift shop, the notice said.

The company said it reviewed future outpatient and inpatient demands and “identified that the inefficient, aging infrastructure of (the existing hospital) is not positioned to service the Windward community long term.”

“To best provide for health care into the future, AHC has determined it needs to create a new and improved inpatient care facility, provide treatments not currently offered in Windward Oahu, expand outpatient facilities to meet the projected increased demand, and consolidate its services in a centralized, natural healing environment,” Adventist said.

Castle hospital, which first opened in 1963, serves more than 130,000 area residents with an existing 160-bed facility staffed by more than 1,000 workers, 330 medical staff and 140 volunteers. The facility was originally built to meet a critical need for medical care in the region, where residents dealt with part-time ambulance service and unpredictable travel times to Honolulu hospitals.

“This is visioning for the future of our campus,” said Kathryn Raethel, Adventist president and CEO. “It’s not that we’re going out to bid next week with it. This is not set in concrete. These are just the things we think will come to be sometime in the future.”

Raethel didn’t have cost estimates or an exact time frame for the long-term project. She said the company had no plans for what it will do with the existing hospital at this point.

The first phase will remodel the existing HPU academic center to house a cancer center, with a 4,000-square-foot radiation treatment area. Existing parking lots parallel to the entrance to the site from Kamehameha Highway will be removed. Parking for 125 cars will be added southwest of the cancer center.

Two four-story buildings will be built in the current soccer field for ambulatory and outpatient services in the second phase of the project. The larger, 19,000-square-foot building will house primary care and wellness services, imaging including gastrointestinal and endoscopy, and outpatient surgical and minor procedures. A cafe and retail shop are proposed for the ambulatory building.

A new, 160-bed, four-story hospital measuring 92,650 square feet will be part of the final phase with a second entry and exit point created along Kamehameha Highway north of the existing entry for emergency vehicles.