The sequencing batch reactor (SBR) plant was constructed on top of an existing facultative sewer lagoon site. The site conditions prohibited deep excavations, so the three basins for the SBRs are shallow, at only 12.5 ft (3.8 m), with a top operating water level of 8 ft to 10.5 ft (2.4 m to 3.2 m). The basins are 94 ft × 120 ft (29 m × 37 m) and have a 2.5:1 slope. They were designed and constructed like a diaphragm, so they can flex a bit without damaging the
structures. The steep slope and flexible walls require that a close eye be kept on settling, or solids could be decanted inadvertently.
The plant also required using horizontal drilling to install a 5300-ft (1600-m) outfall that reaches into the shipping channel of the Columbia River, which flows into the Pacific Ocean soon thereafter. The 18-in. (450- mm) steel outfall pipe was installed by a separate contractor that specializes in horizontal directional boring. The pipe extends 4400 ft (1340 m) underneath the river. Because the outfall pipe is steel and protrudes into salty water, it also includes a cathodic protection system. In addition to the treatment plant, the city has allowed a local seafood processor to
discharge into the outfall. This has enabled the processor to cease discharges into the Skipinon River, which had degraded in water quality.