An affiliate of Houston-based Hines Interests has purchased a four-acre parcel of land at 36 River St. in Waltham for $13.5 million, with plans to build a luxury apartment complex on the site.

Acadia on the Charles LLC, a joint venture of Boston-based Saracen Properties LLC and Gate Residential, had received approval and permits last year for 200 residential units and 400 garage parking spaces on the Charles River site. Hines MIP River Street LLC will undertake construction of the project.

Amenities in the project will include both active and passive outdoor courtyards, one with a pool and deck, the other with a resident-only accessible courtyard with patios, according to a news release.

In-house amenities will include a resident’ clubhouse area with a kitchen, dining room, library, game room and 20 seat-theater. A health facility, computer lounge and coffee bar are also planned. An indoor/outdoor fireplace with deck will overlook the Charles River. Many units will have private balconies or patios that will open to the pool and courtyard areas.

Saracen President Ted Saraceno said in a statement: "Acadia will be a very successful project for Hines. This is a vibrant neighborhood experiencing strong growth in commercial, residential and retail businesses. Ultimately, the project was able to attract a top-tier buyer because it was designed to the highest standard and the project team was first-class."