Amazon already occupies nearly a fifth of Seattle office space. And according to commercial real estate watchers, that slice of the pie is about to get even bigger. The company is rumored to have a pending lease on the office portion forthcoming Rainier Square project, a 58-story structure set to open in 2019 next to Rainier Tower. This would add 710,000 square feet of office space to the Seattle-based giant. Both Amazon and development company Wright Runstad & Co. have been cagey about the lease, but sources state that the major issues have been worked out, and only final details remain. Construction will commence on the project within the next few months.