Salem draws water from the North Santiam River, downstream from Detroit Reservoir. Nutrient runoff from agriculture and industry, temperature fluctuations and other factors could have created cyanotoxins in the water. Cyanotoxins release a blue-green algae bloom upstream of Salem’s water intake.
Salem's water travels through a fine-sand filtration system to remove impurities such as algae, sediment and pathogens. The water trickles down through the filter beds and through a biological layer called a Schmutzdecke, which is full of good algae, insects and bacteria. Some, but not all, cyanotoxins can be removed in this step.
Salem is piloting a new treatment system that will add activated carbon to the water at the river intake to absorb cyanotoxins. Mixers floating in the canal keep the carbon suspended in the water to maintain contact throughout. After treatment, water flows into a basin where the carbon settles out with the help of accelerating agents. The water then flows through a roughing filter to remove any remaining carbon.
Salem can reduce the concentration of cyanotoxins by diluting treated river water with ground water. The city has several wells near its treatment plant on the river, and can also connect to the drinking water systems in the nearby cities of Keizer and Stayton, which use well water.
After treatment, Salem adds three chemicals to the finished water: Fluoride helps prevent tooth decay in children. Soda ash adjusts the pH, to keep lead and copper from leaching from household plumbing. And chlorine disinfects the water. Chlorine can also help reduce cyanotoxins.
The water is then sent to a water reservoir, where is stays until it is needed.
NOTE: Not all cyanotoxins lead to all of these health impacts.