Water Treatment & Water Quality

The intake for the water system is located on the Naches River about 6 miles west of Yakima. Water is diverted from the Naches River at the confluence of the Tieton and the Naches Rivers by the Bureau of Reclamation through the Wapatox Canal. The intake structure has a number of fish protection facilities. Water leaves the intake and travels to the Water Treatment Plant through a 54-inch diameter concrete main.

Water Treatment Plant

At the Water Treatment Plant, ACH, aluminum chlorohydrate, is added to the water in the “flash mix” to cause microscopic impurities in the water to clump together. The ACH and the water are mixed rapidly by the flash mixer. The resulting larger particles will be removed by filtration. A cationic polymer is also added to enhance the coagulation process.

The water is slowly mixed in two contact basin, 500,000 gallons each, allowing the coagulated particles to become larger and stronger and are now called “floc.” As these floc particles mix in the water, bacteria and other microorganisms are caught in the floc structure. A non-ionic polymer is added at the end of the basins to improve the next process.

The water flows by gravity through four large filters of anthracite coal and silica. The floc particles are removed in these filters. The filters are sized for a flow of 25 million gallons of water each day. The rate of filtration is adjusted to meet water consumption needs.

Fluoride is added to the water to aide in the prevention of dental cavities.

Chlorine is added to the water at the flash mix for pre-disinfection. The chlorine kills or inactivates harmful microorganisms. Chlorine is added again after filtration for post-disinfection. The water is held in the 48-inch transmission main between the plant and Gleed for a specified time to allow the chlorine to disinfect the water. Chlorine is generated on site as a 1% bleach solution.

Corrosion Control
The pH of the water is adjusted with sodium hydroxide, commonly called caustic soda. Caustic soda is fed into the water after filtration.

Taste and Odor Control
Powdered activated carbon (PAC) is occasionally added for taste and odor control. PAC is added to the flash mix.

Water Quality
Water testing is conducted throughout the treatment process. Items like turbidity, pH and chlorine residual are monitored and recorded continuously. Some items are tested several times per day, some once per quarter and others once per year.

Getting the Water to You
As the water leaves the Water Treatment Plant, it flows by gravity through a 48-inch pipeline. Several pumping stations in the distribution system deliver the water to one of five covered reservoirs at higher elevations and/or to homes, businesses or for industrial use.

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