The City of Selah wastewater facilities consist of a sewage collection system and a wastewater treatment facility. The sewage collection system consists of approximately 110,000 linear feet (LF) of pipe, with a majority of the pipe being 8-inch diameter. The wastewater treatment facility was originally constructed in 1936, with upgrades and expansions in 1949,1968,1975 and 1987. Today the plant is an activated sludge plant operated in an extended aeration configuration. The wastewater flow path through the treatment plant begins at the influent building where wastewaters pass through a sewage grinder and are then pumped to one or both of the two aeration basins for biological treatment. Aeration basin effluent gravity flows to the chlorine contact chamber for disinfection prior to discharge to Selah Ditch. Solids which settle in the clarifiers are either pumped back to the aeration basins(return activated sludge) for use in treating influent waste, or are removed from the process (waste activated sludge) by pumping to the aerobic digester where solids undergo additional biological decomposition and stabilization. Wet sludge is removed from the aerobic digester by hauling in a tanker truck to the sludge storage and land application site located at the Yakima County Cheyne Landfill.

An industrial pretreatment facility for the pretreatment of food processing wastes was constructed in 1985. Pretreated industrial wastes flow into the main Selah wastewater treatment facility and are mixed with domestic waste where they undergo further treatment.

Within the last few years, Selah has developed a number of studies to identify system needs and improvements. These include:

  • Wastewater Facilities Comprehensive Sewer Plan – 1996
  • Wastewater Treatment Facilities Plan for maintaining Adequate Capacity – 1996
  • Wastewater Treatment Facilities Biosolids Disposal and Composting Plan – 1996
  • Wastewater Treatment Facilities Disinfection Report – 1997
  • Wastewater Treatment Facilities Residual Solids Management Plan – 1997