Groundwater is often found in aquifers, which are expanses of underground fractured rock between impermeable bedrock, allowing water to seep into the ground and be kept within the fractured rock with some amount of flow through the open space. While the City uses surface water for most of its drinking water, we also operate an Aquifer Storage and Recovery (ASR) well system, located in South Salem to store and recover treated water.

During the winter months when river flows are high and water demand is low, treated drinking water is injected into the naturally formed aquifer 350 feet below Woodmansee Park. Then, during the summer months when river flow is typically at its lowest and water demand is high, water in the aquifer is pumped back to the surface, sampled for quality, and sent back into the distribution system to be used by customers. The ASR facility treats the recovered water with sodium hypochlorite (chlorine) for disinfection and adds sodium hydroxide for pH adjustment before it enters the distribution system.

This map shows the general boundary area for the aquifer. The City takes extra precaution in this area for contaminants such as gas and oil spills, underground storage tanks and sewer systems.

Cross-section diagram of the aquifer storage and recovery system at Woodmansee Park, showing a well pipe extending through soil and basalt rock layers to store treated drinking water underground and recover it later for city use.