AutoNation BMW of Bellevue is currently expanding storage of inventory vehicles by redeveloping a plot of land to construct a new multi-story parking garage. This large three cell vault was constructed to facilitate storm water runoff from the newly developed site. The design and construction of this detention vault was unique in that site-cast tilt up wall panels were utilized in lieu of cast in place wall panels. The vault’s capacity is nearly 600 thousand gallons to meet a 100 year storm design. The lid is constructed of 165 pieces of 12 ½” thick by 4’ wide prestressed, precast untopped hollow core slabs. The slabs span in length from 14’ to 21’ and are designed to support a 45 kip outrigger loading from a Fire Truck or a 250 psf uniform live load with up to 5.0’ of soil and asphalt cover.