Additional Drinking Water Treatment in Algal Season (April to October)
Additional monitoring and water quality sampling occurs above Geren Island, in the North Santiam River watershed (Salem's drinking water source) during algal season. Based on information learned in 2018, the City can now adjust drinking water treatment processes based on watershed conditions and the water quality data received. Additional treatment processes used to remove cyanotoxins and to ensure safe drinking water include:
- Acetic Acid (added to Slow Sand Filtration)
- Increased chlorine dosage
- Powdered Activated Carbon (PAC)
In addition, the City is now investing close to $50 million dollars for the design and construction of an ozone treatment facility on Geren Island. This new facility is anticipated to be completed in the Spring of 2021.
Preparation for algae season
In May 2018, for the first time, cyanotoxins from the die off of a certain type of blue-green algae made their way through the slow sand filters and were detected at Aldersgate, the entrance to our distribution system. As the algal season progressed, the City began to add Acetic Acid (vinegar) to the water as it flowed into the slow sand filters. This helped the biological surface layer to grow, and boosted the ability of the Schmutzdecke to remove cyanotoxins from the water. As a result, and in preparation for the coming algal season, the City will begin to add acetic acid to the slow sand filters in April.
Added treatment steps to manage cyanotoxins
We have added treatment steps—increasing chlorine dosage and using powdered activated carbon to control cyanotoxins. These additional barriers, along with slow sand filtration, reduce and eliminate cyanotoxins if they enter the water treatment plant. Until ozone treatment is available, increased levels of chlorine coupled with powdered activated carbon are the most effective way for us to protect our community from cyanotoxins. These treatment steps will be used until the long-term solution—ozone treatment—is in place in spring 2021.
Increased chlorine dose
The Environmental Protection Agency requires that chlorine be added to drinking water treatment processes for disinfection when surface waters (streams, rivers, lakes, etc.) are the source. For this reason, chlorine is always used at Geren Island as final step in the treatment process.
If cyanotoxins are present, the level of chlorine used in our water treatment will be slightly increased, enough to destroy the cyanotoxins. Then, using a type of salt (sodium bisulfite), chlorine levels are reduced to the normal levels as the treated water leaves the plant.
We anticipate the changes to how the water tastes and smells due to the additional treatment steps will not be noticed by most residential customers. Nor will these changes impact our industrial or commercial users. We will be conducting water quality and tastye studies to ensure our customers continue to receive the highest quality water and consistent aesthetics.