Capacity limitations in Tacoma’s existing stormwater system were responsible for flooding in the lower downtown area during significant rain events. Coupled with expected population growth in the coming years, the City hired the team of JWF and Kennedy-Jenks as the design-builder for 2,988 feet of storm and sewer pipelines including 1,900 feet of RCP and PVC via open cut and 1,088 of 72″ microtunnel.
The project includes the installation of 2,988 LF of storm and sewer pipelines, including 1,251 LF of 60” RCP, 394 LF of 48” RCP, and 255 LF of 12” PVC through open cut excavation. Additionally, 1,088 LF of pipe was installed via microtunneling in three separate drives. The first drive was 483 LF of 72” RCP, the second drive was 265 LF of 72” steel casing, and the third drive was 340 LF of 72” RCP. Microtunneling was used to navigate around a BNSF rail corridor and a major arterial/light-rail corridor. The section where tunneling was used was also upgraded to complete the Prairie Line Trail multi-use path.
The outfall, designed to support stormwater drainage of more than 90,000 gallons per minute, provides stormwater conveyance capacity for future growth in the downtown area. At that flow rate, it would take about seven minutes to fill an Olympic-size swimming pool.