One of the great things about Portland’s water system is that we have a second high-quality water source, the Columbia South Shore Well Field (CSSWF), that we can use to supplement or replace the Bull Run supply during especially dry summers or during emergencies. Over the last year, the bureau has been working on a project to ensure that water from one of the three aquifers in the CSSWF, the Blue Lake Aquifer (BLA), continues to be available for years to come.
The BLA is a small yet productive aquifer in the eastern part of the well field with five production wells (Wells 12, 13, 17, 18, and 19) that can produce over 45 million gallons per day. That’s almost as much as all the other 22 wells in the CSSWF combined. Unfortunately, three of these wells have developed a water quality issue, increasing concentrations of manganese, that has lead these wells to be used less often or only during emergencies. Manganese is a common metal found in rock and soil. Manganese can cause water to become discolored, and at higher concentrations is known to have negative health effects.
Historically, two wells (17 and 18) have had high concentrations of manganese and have been studied for several decades. However, during the 2018 summer augmentation operation, a third well, Well 12, showed a steady increase in manganese. This trend, if it continued, threatened the ability to use Well 12 as a normal part of future supply operations and our ability to meet customer needs.
In order to better understand the risk to Well 12 and the other two low-manganese wells in the BLA (Wells 13 and 19), the Water Bureau hired a team from Stantec and Groundwater Solutions Inc., experts in the fields of hydrogeology, hydraulic modeling, geochemistry, and engineering, to determine the source of manganese at Well 12, determine if running certain wells together increased the risk to the remaining low manganese wells, and identify short- and long-term solutions.
The project team presented their findings to the Groundwater Steering Committee, a group of stakeholders from across the bureau, earlier this year. Through modeling and isotope analysis, it was determined that the Sandy River Delta deposits to the north and east of the BLA are the likely source of manganese at Well 12. This is the same source that has historically plagued Wells 17 and 18. Modeling showed that manganese will continue to be an issue at Well 12 and will likely get worse if nothing is done. Furthermore, modeling showed that there is risk of elevated manganese to the other two low-manganese wells (13 and 19), especially if the bureau stops using Well 12 for supply.
The project team presented a number of long-term alternatives for addressing the manganese problems in the BLA that include: maintaining the status quo; pumping water from Well 18 to hydraulically protect the other wells; pumping in filtered water from the Bull Run or clean water from another well to reduce manganese in the aquifer; replacing the affected wells with a new well in the western BLA; and treating the manganese via filtration. The project team also identified short-term alternatives that the bureau will be implementing while additional data is collected to identify the best long-term alternative.
Over the next several months, the bureau will be finalizing this project and moving forward with collecting additional data and initiating new work that will ultimately inform which approach the bureau chooses to ensure that we continue to have plentiful, high-quality water from the BLA for years to come.