WWTP Outfall Replacement City of Pasco
Project Details
Owner: City of Pasco
Location: Pasco, WA | August 2023 – April 2024
Advanced American Construction (AAC) completed Phase 2B of the Wastewater Treatment Plant Improvements project for the City of Pasco, replacing an undersized outfall pipeline to increase system capacity and improve water quality. The project involved removing the existing 1,250-foot, 24-inch outfall pipe and installing approximately 1,600 feet of new 42-inch high-density polyethylene (HDPE) outfall pipe to convey treated effluent to the Columbia River.
AAC constructed a sheet pile–lined trench at the river’s edge to provide a controlled transition from land-based excavation to in-water work. The outfall pipeline extended approximately 1,250 feet into the Columbia River, where a derrick barge was utilized for pipe installation. AAC assembled the HDPE pipe string, launched it into the river, and carefully sank it into its final alignment before completing dredging and backfilling operations.
Tapani Inc., AAC’s subcontractor, performed the majority of the landside excavation and HDPE fusion work. Once the new outfall was installed and effluent flow was successfully transferred, AAC backfilled the trench, demolished the existing outfall pipe, and restored the site. The project also included the construction of sheet pile and retaining walls, as well as the removal and reinstallation of a temporary pedestrian pathway.
Despite challenging winter weather conditions and working within the Columbia River, AAC executed the dredging, material handling, stockpiling, and backfilling operations safely, efficiently, and on schedule.
Project Highlights
- 1,250 feet of pipe was installed underwater in the Columbia River.
- Finished pile driving and removal in the required in-water work window
- Completed the system swap out during the two day window given on project with no issues
- Dredged and installed 42” pipe, backfilled, set concrete anchors, and demobilized existing concrete WWTP pipe and outfall in the required IWWW.
- Replace existing 1,250 foot long 24-inch outfall pipe with 1,600 feet of 24-inch HDPE outfall pipe.
- 25,120 CY of Backfill and Fish Mix Placed in the Columbia River.