Could the whole hill go crashing down? County and ODOT address local concerns with HWY 213 landslide
Clackamas County and the Oregon Department of Transportation together held two informational sessions at a public meeting on Tuesday, Feb. 13 to provide updates and answer questions regarding the Highway 213 landslide. It was a standing room only crowd during the first session at Arrowhead Golf Club's Payne's Stewart Meeting Room.
ODOT representatives offered some details on the status of the slide and ODOT's work to remediate the effects.
"As you all know, an ancient landslide has reactivated in the area near Spangler Hill," said ODOT community affairs representative Kimberly Dinwiddie. "And this slide has been dormant for several decades or more. However, the record-breaking rainfall that we had last winter overwhelmed the groundwater system."
Dinwiddie explained that the slide is still moving up to inches per day.
One crowd member bravely asked the question others were certainly thinking: could the whole hill go down in one swift movement?
Dinwiddie responded that they are monitoring the movement daily and are willing to close the highway if it becomes unsafe for travel. She expects that they would be able to close the highway before any drastic movement would pose a safety risk to drivers.
In response to the effects of the slide on the highway, in October, ODOT completed some pavement repairs. They dug down and installed geogrid, which is a high-strength plastic material. It strengthens the road and gives it some flexibility to accommodate landslide movement that ODOT expected, according to ODOT representative Katelyn Jackson.
While they worked on those repairs, they engineered a plan to address the landslide itself, and the solution they came up with is horizontal drains.
In January, ODOT began the work to install 40 drains 80 feet below the highway, which pour out into Milk Creek. At this point, 10 drains have been installed.
"What we are finding is that…each drain has pumped out nearly 300 gallons of water a minute," Dinwiddie said. "When the first drain got installed a couple of weeks ago, we had 20 gallons of water per minute. We were happy with that. So, we started pumping out 300 gallons. That was evidence that the system that we're putting in place is working."
For reference, a kitchen sink pours out approximately 2.5 gallons of water per minute.
But one area resident is concerned that draining groundwater may impact domestic wells.
"If they take the groundwater down, is that going to cause the wells at some point to need to be drilled deeper?" Bill Day said. "That's one of my main concerns."
Others expressed concern about flooding Milk Creek.
Dinwiddie said that they expect the drains to pump out less water as the weeks and months go on, which will reduce the potential for secondary effects.
All 40 drains should be installed by the end of spring and are expected to help stabilize the slope in the Highway 213 area.
ODOT is monitoring the highway daily. They have and will close lanes if pavement conditions become too bumpy for traffic. But ODOT representatives assured crowds on Tuesday that the road conditions are safe for travel.
For area residents concerned about the safety of their own homes, ODOT and the county suggest they seek the expert advice of a geotechnical engineer or comparable expert, since as government agencies, they cannot direct or suggest the appropriate measures to be taken on private property. However, ODOT has asked the Oregon Department of Geology and Mineral Industries to partner with them to study the larger area and help provide that information to area residents, according to Jackson. They are waiting for a response.
At least one concern still lingers: traffic. Eldorado Road remains closed at its southern intersection with the highway and will remain closed until drains can effectively improve conditions.
"It's not a big deal," said Day who lives on Eldorado Road. "It's about a 2-mile extra trip. It's just inconvenient."
The inconvenience may continue, especially as ODOT plans to begin construction nearby this winter on the Safety Improvements Project at South Union Mills Road, where they will level the crest of Highway 213, add a right-turn lane and shoulder at Union Mills and more. A full story on that project will follow.