Coffin Butte Landfill is situated in one of the wettest parts of the Willamette Valley, on geologically complex land. This poses significant environmental problems. The wetter the climate, the more methane (potent greenhouse gas; 80-plus times more potent than carbon dioxide) and leachate (“garbage juice”) it generates; the complex geology creates potential risk of ground and surface water contamination. A properly situated landfill would be in a dry climate, on clay soils, and away from human habitation. Coffin Butte Landfill is none of these.
VERY WET CLIMATE
Coffin Butte is in one of the wettest parts of the Willamette Valley… averaging more than 65 inches of rain per year. That’s nearly 2 feet more rain per year than downtown Corvallis! It’s wetter than Eugene, wetter than Salem, and wetter than Portland. (For comparison: the Columbia Ridge Landfill in Gilliam County, Oregon averages 13 inches per year, and the Roosevelt Landfill in Klickitat County Washington, averages less than 8.5 inches per year.)
Why is Coffin Butte so wet?
(a) Coffin Butte is north of the rain shadow of Marys Peak, and
(b) Coffin Butte is part of of a “salient” of the Coast Range, seen as a patch of blue on this map of rainfall.
Methane leakage. Wetter = worse. The microbes that produce methane from trash depend on water. Water seeping into garbage becomes acidic, allowing it to leach nitrogen and phosphorus from the waste, and then making these nutrients available to the anaerobic bacteria that produce methane. More water = more methane. While carbon dioxide is longer-lived, methane is far more effective at trapping heat in the atmosphere. Over the first two decades after its release, methane is more than 80 times more potent than carbon dioxide in terms of warming the climate system.
Leachate =“garbage juice”. Wetter = worse.
What is leachate?
Leachate is water that has been contaminated with dissolved chemicals after seeping through garbage. Dangerous contaminants in leachate can include dissolved metals such as lead and manganese, toxics such as arsenic, and carcinogenic industrial solvents such as TCE (trichloroethylene) as well as PFAS (“forever chemicals”).
What do they do with the leachate?
Currently leachate from Coffin Butte is hauled away in tanker trucks — over 30 million gallons per year. Most goes to the municipal wastewater treatment plant in Corvallis, where has to be mixed with city sewage before it’s treated to levels are allowed to be discharged into the Willamette River.
Why can’t they just leave leachate in the landfill?
If leachate levels build up inside the landfill, this allows water pressure to build up inside, just like water above a dam. High water pressure can cause leaks, either out the sides of the landfill where it contaminates surface waters [this has happened at two of Republic’s landfills in California], or through the bottom of the landfill where it contaminates groundwater.
Can’t they just keep rainwater out of the landfill?
The operators try to minimize rainwater infiltration by keeping most areas covered with a system of tarps. But there’s no way to keep water out of the active disposal area, which is at least two acres at any one time.
COMPOSITION OF ROCK AND SOILS ON WHICH IT SITS
Coffin Butte is complex geology on a steep hillside
What kind of geology?
The bedrock forming Coffin Butte, and Tampico Ridge to the south, is mainly marine basalts. These rocks, part of the Siletz River Volcanics formation, are understood to have formed by lava flowing out of undersea volcanoes, about 58 million years ago (early in the Eocene epoch). As hot lava cooled rapidly in the salt water of the ocean, it formed piles of irregular shapes known as “pillow basalts.”
Over the next 20 million years, as that slab of seafloor gradually slid beneath the edge of North America, the top layers were scraped off the top of the slab. The pillow basalts, along with layers of seafloor sediments, piled up on the edge of the continent to form the Coast Range, as part of what geologists call an “accretionary wedge” [see https://www.usgs.gov/glossary/earthquake-hazards-program#A for an illustration].
So these rocks started off complicated, and became even more jumbled during formation of the Coast Range mountains.
Can water really flow through basalt?
Groundwater moves through basalt mainly through cracks also known as “fractures.” Most households and farms in the Tampico area draw their water from wells drilled into “fracture zones” in the basalt. These are parts of the rock with more fractures than other parts.
Why is this a problem?
Water moving through fractured basalt is much more difficult to predict than water moving through sediments such as sand or gravel. This is because the networks of cracks and fracture zones are very irregular.
Also, scientists have learned that contaminants moving through fractured bedrock have less chance to “disperse” (spread out and become more diluted) with distance from a pollution source, such as a leaking landfill.
This means that contaminants could possibly reach wells in dangerous concentrations, even farther away than would be expected in sand or gravel aquifers.
Can’t they just “monitor” it?
The same things that make ground water flow hard to predict also make it hard to design a monitoring program to detect polluted water leaking out from a landfill through this type of rock.
If you don’t know where the main fracture zones are, or how they’re connected underground, you don’t know where you need to put monitoring wells to check for leaks. There might be no way to detect a problem until after contaminants reach household wells, and residents have already been exposed to carcinogens and other toxics for months or years.
Why is the steep hillside a problem?
Locating a landfill on a steep hillside gives another way for water to get into the landfill, causing more methane and leachate problems.
This is because groundwater levels will be higher on the uphill side of the landfill, especially during the rainy months when the water table is close to ground surface.
High groundwater levels outside the landfill could result in high pressures pushing water into the landfill from the uphill side, possibly creating new leaks in liners that were mainly designed to keep contaminated water from leaking out of the landfill.
The risk of this type of problem continues for many years, even after the landfill closes, the main corporate owners have left town, and drainage and liner systems begin to fail with age.
Benton County could be left with no options but to deal with a smaller “shell” company, with limited resources to handle liability for future problems.
What about earthquakes?
Coffin Butte, like our entire region, is at risk from a “megaquake” of magnitude 9.0 or greater from slip on the Cascadia Subduction Zone.
Impacts on the landfill could include:
– Slope failures and liner failures caused by intense shaking that could last up to 4 minutes.
– Leakage of contaminated water into surface waters and groundwater.
– Shearing off of methane wells and rupture of liners meant to contain methane.
– Fires fueled by methane leaks.
– Loss of electrical power to maintain critical systems, for a period of weeks.
– Additional fires and leaks spawned by aftershocks.
The consequences of these impacts will add complications and hazard to what would already be a major crisis in the region.
Coffin Butte is also within 2 miles of the Corvallis Fault. [https://www.corvallisoregon.gov/ds/page/earthquake-preparedness] At this time, it is not known if this fault is active, or if it could be triggered by a megaquake on the Cascadia Subduction Zone.