5/29/2013 3:51:15 PM
GeoSyntec, the firm that engineered the wall Waste Management wants to build on the Highway 18 side of the dump, has assured DEQ (Oregon's Department of Environmental Quality, which decides whether or not the wall gets built) that the wall will be strong enough to withstand a magnitude 8.5 earthquake.
But are GenSyntec's assumptions really sound? Let's consider:
Under EPA requirements, if the horizontal acceleration generated by an anticipated earthquake is more than 0.1g, the entire landfill must be studied for stability before the wall or any other expansion can be approved. GeoSyntec found that the horizontal acceleration from the earthquake it studied would be exactly 0.1g.
Geosyntec reached the 0.1g figure by using:
• A peak ground acceleration of 0.415g instead of the 0.58g shown on US Geologic Survey (USGS) charts
• 75km distance from the site of the quake instead of the 50km distance USGS uses
• A theoretical return period of 2,357 years instead of the actual historical average of 400 years (five 9.0 magnitude quakes in the past 2000 years)
• The upper limit of 12" of bottom interface movement allowed under California Standards instead of the lower limit of 6" (using GeoSyntec numbers, the actual movement would be 10")
• A single selected bore hole on the uplands where there is 45 feet of better soil rather than a bore hole in the lowlands with 25 feet or less of good soil
• Ignoring failure of the liners at the top of the landfill due to amplification 2.5 times the "g" forces
If any one of these assumptions proves optimistic, the entire analysis fails. Clearly this is not "conservative" engineering. Moreover, even with these assumptions, the wall fails to meet the factor of safety for slope stability for earthquakes and will fail at 0.073g when 0.1g is predicted.
The landfill is not safe in even a moderate earthquake let alone the M9.0 Cascadia Subduction Zone earthquake experts predict. We should close Riverbend now.
Geosyntec reached the 0.1g figure by using:
• A peak ground acceleration of 0.415g instead of the 0.58g shown on US Geologic Survey (USGS) charts
• 75km distance from the site of the quake instead of the 50km distance USGS uses
• A theoretical return period of 2,357 years instead of the actual historical average of 400 years (five 9.0 magnitude quakes in the past 2000 years)
• The upper limit of 12" of bottom interface movement allowed under California Standards instead of the lower limit of 6" (using GeoSyntec numbers, the actual movement would be 10")
• A single selected bore hole on the uplands where there is 45 feet of better soil rather than a bore hole in the lowlands with 25 feet or less of good soil
• Ignoring failure of the liners at the top of the landfill due to amplification 2.5 times the "g" forces
If any one of these assumptions proves optimistic, the entire analysis fails. Clearly this is not "conservative" engineering. Moreover, even with these assumptions, the wall fails to meet the factor of safety for slope stability for earthquakes and will fail at 0.073g when 0.1g is predicted.
The landfill is not safe in even a moderate earthquake let alone the M9.0 Cascadia Subduction Zone earthquake experts predict. We should close Riverbend now.
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