If you live in the Portland area and haven’t explored the Columbia River Slough for yourself, you’ve probably at least seen signs for the little waterway en route to PDX. The slough is an 18-mile creek/wetland that flows from Fairview Lake into the Willamette River near Kelly Point Park.
It’s also home to the Columbia South Shore Well Field, a system of 27 drinking water wells. On this 90-degree afternoon, I took a tour of the slough with a few folks from the Portland Water Bureau and the Columbia Slough Watershed Council.
The wells in the slough provide 3 to 5 percent of the drinking water for Portland. But I learned that they’re a pretty important backup to the surface water that the city relies on most of the time. During a “scouring event”— basically a big storm or snow melt — nearby rivers and reservoirs can become too silty for the city to draw from for drinking water.
That’s when the bureau turns to the wells on the slough. When surface water becomes undrinkable, the city can pump 2,500 gallons of water per minute from each well.
The well field is protected by a city ordinance to prevent drinking water contamination.
Without the wells, Portlanders would have to boil their drinking water after a major storm event.
“Portland is pretty lucky to be home to two sources of water — lucrative surface water and protected, productive groundwater,” Sarah Santner with the Water Bureau told me. “The wells provide almost complete backup.”