Residents of Lewis County are no strangers to natural disasters.
Along with flooding, seasonal heavy rain brings another natural risk many often don’t think about — landslides.
For residents on Swanson Drive just off of Cooks Hill Road in Centralia, that risk is something they have to live with every day, said Patrick McPeak, who has been there for nearly 20 years.
Though Swanson Drive is used by McPeak’s neighbors to access their own homes, the land the road is on is actually part of his property.
The areas including McPeak’s property vary between “possible landslide in the area” and “high confidence in extent or nature of landslide” on the U.S. Geological Survey’s (USGS) landslide inventory and susceptibility map.
Swanson Drive is right at the foot of a slope on the east end of the Cooks Hill area near the banks of the Chehalis River. The elevation above the slope’s toe rises from about 290 feet to 350 feet in the span of less than 140 feet, a slope averaging approximately 23 degrees, according to topographical maps of the area.
“The toe of the slope is a really important area. It is the point where if it’s disturbed, it’s really the last thing holding the slope back,” McPeak said.
And the slope apparently has been disturbed, he said.
“My neighbors up there, they’ve found cracks that have appeared,” McPeak said.
Swanson Drive had work done to widen it in 2006 as was required when the area was incorporated into Centralia’s urban growth area (UGA).
McPeak believes the slope’s toe was disturbed at that time and that the landslide threat has been exacerbated.
One of McPeak’s neighbors who also uses Swanson Drive, Dennis Shimmel, obtained the permits from the city and hired the contractor to widen the road.
McPeak believes that instead of preserving the shape of the slope’s toe during road widening, construction crews dug directly into the toe in order to expand the road.
“The permit was only for widening, and if you read the permit, it says they weren’t supposed to remove more than 499 cubic yards (of earth),” McPeak said. “The volume of earth that was removed from here was way beyond that number” under the description of work.
On both the building permit and excavating and grading permit issued by the city in 2006, it simply says “up to 499 cu. yards of fill for road widening.”
Ever since the earth was removed from the toe of the slope to widen the road, McPeak has been noticing evidence of increased erosion, from crumbling sandstone, accelerated erosion and leaning trees, he said.
According to McPeak, more than 20 mature trees were removed and the cut into the toe of the slope is nearly verticle, approximately 70 degrees.
Water seepage occurs on Cooks Hill, too, as springs exist in the area, and this water increases the risk, he said. Many large old trees, with roots that helped stabilize the soil, were also removed for the road expansion.
“You would think the city would really say, ‘We need to send somebody out to look at the situation, show us exactly what you’re doing,’” McPeak said. “They did nothing. For the sake of growth, they basically just said, ‘Fine, go ahead and do whatever you want to do.’ Not realizing the potential risk.”
After years of noticing more erosion on the toe of the slope, McPeak paid for a landslide assessment to be done by Pacific Testing & Inspection in 2014.
The results of that inspection found natural slopes in the area with grades of at least 50% and soil along Swanson Drive generally was composed of 4 to 6 feet of silty clay with sand overlying dense, fissured sandstone. The sandstone had fractures with discoloration, indicating groundwater seepage, McPeak said.
That underlying sandstone is now visible along Swanson Drive.
The report concluded that the road widening had increased landslide risk in the area and additional geotechnical investigation was needed.
“We believe that the development of the driveway created intensified, unstable slope conditions,” the 2014 inspection report said.
The report also cited Washington state Department of Natural Resources maps which have the hillside listed as an area with medium and high slope instability. Given this knowledge, McPeak believes the City of Centralia should have demanded a geological survey and civil engineering study from the contractors before granting them permits to work.
He met with city staff following the Pacific Testing report to talk about the results.
“We gave them a copy of it, thinking something was going to happen. Absolute crickets,” McPeak said.
In 2017, McPeak wrote a letter about the report and landslide threat to the Centralia city attorney at the time, but again received no response.
The city has approved contracts for other minor work in the area including adding rip rap stone to help stop erosion happening from rain runoff. But nothing has been done to address the landslide threat, McPeak said.
City staff have been responsive with both McPeak and his neighbors concerning the addition of rip rap stone, among other issues, but not the landslide threat, he said.
At this point, though, McPeak isn’t sure anything can be done to avert the threat, but he said he is still tired of being ignored.
However, he understands why city staff may not be chomping at the bit to address the issue, as mitigating landslide risks is never easy.
Often there isn’t much that can be done, aside from replanting trees and plant-ground cover or diverting water and debris flow — and there isn’t much room to do so on Swanson Drive. Any further disturbances to the ground only add to the landslide risk, McPeak said.
“There have been other cities that have tried to remediate the problem, and they made it worse,” McPeak said.
He hopes the city carefully considers any possible future development it permits in the area as he does not want any further damage done to the slope toe’s integrity.
On top of a public records request for permits and emails between the city and McPeak and his neighbors, The Chronicle reached out to Centralia city staff members in the public works and community development departments, along with City Attorney Kyle Manley, for comment.
Questions included whether a followup inspection to the 2006 road-widening work was ever completed, whether the city was considering attempting any landslide mitigation in the area, and if the city has a map listing landslide danger areas or utilizes the USGS landslide inventory and susceptibility map for projects.
According to Manley, the city does have maps including landslide risk zones included within its comprehensive plan, and both the city’s municipal code and Lewis County code have sections regulating construction within hazardous areas.
“Neither of these chapters completely prohibit all development activities within critical areas, but additional requirements, technical reports, or studies may be required,” Manley said in an email to The Chronicle. “When the development activities are happening on private property, the property owner is responsible for completing the reports or studies and performing any mitigation work recommended by them.”
As for the post-2006 road widening inspection, since Swanson Drive is not a public street in the UGA and considered a “shared driveway,” the city has limited regulatory authority over activities within it.
Manley added any authority the city does have is delegated via an interlocal agreement with Lewis County.
According to that interlocal agreement, the city’s building code and development standards apply to the construction of any structures or infrastructure improvements relating to water and sewer service, first responder access and frontage improvements on public streets.
“However, Lewis County's critical areas regulations apply instead of the city's,” Manley said. “Any geological assessments or (landslide) mitigation efforts would be under the laws and jurisdiction of Lewis County, and any unauthorized work the Shimmels did on the McPeaks' property, and the ramifications/effects thereof, is a private civil matter between the parties.”
Centralia Municipal Code on geologically hazardous areas can be found online at https://tinyurl.com/5cvyym2r.
Lewis County Code on hazardous areas can be found online at https://tinyurl.com/3t2mpbha.
To view the USGS landslide inventory and susceptibility map, visit the USGS’ website at https://tinyurl.com/yhxrn8rp.
For the geological hazard area maps utilized by the City of Centralia, visit the city’s website at https://tinyurl.com/22rzrard.
