This project consists of two separate underground storm water detention vaults for storm water runoff for a new apartment complex in Edgewood, WA. The two vaults have a total footprint of 1,200 S.F. and 25,600 S.F., respectively, and range in depth from 7’ to 10’. Due to site restrictions, the larger vault is configured in a “U” shape such that it is kept under parking areas and does not interfere with the apartment building foundations. The lids for these vault are constructed with 352 pieces of 12 ½” thick x 4’ wide prestressed, precast untopped hollow core slabs. The hollow core slab lengths range from 14’ to 23’, and are designed to support HS25 truck loading and, at some locations, up to 9’ of soil and asphalt cover.