Numerous studies of hydrogeologic conditions have been conducted by Waste Management's consultants. These are based on boring logs that are recorded each time a well or piezometer is drilled. Monitoring wells are used to draw water samples for lab analysis, and to measure the elevation of the groundwater surface.
Elevations of groundwater relative to bottom of waste
Waste Management's consultant prepared a report in November 2012 that assesses groundwater elevations relative to the elevation of the bottom of waste at the landfill. As shown in this report, the elevation of groundwater is higher than the bottom of waste in portions of the landfill. It is important to note that the waste lies above a liner that prevents the escape of contaminants. The liner system has become increasingly substantial as new sections of the landfill have been built, to provide a more effective barrier between waste and groundwater.
The report does not evaluate the three oldest cells (Modules 1 through 3), whose liner systems consist of low-permeable soil but do not include plastic geomembranes. This is because the consultant was unable to find base grade information for these older landfill cells.
Water quality 1200-Z permit
Documents related to the 1200-Z permit for Riverbend Landfill include:
There is localized groundwater contamination, as indicated by the presence of volatile organic compounds in one groundwater monitoring well. Volatile organic compounds are of particular importance in evaluating a landfill's effects on groundwater for a couple of reasons. They move fairly quickly through groundwater and therefore provide an early indication of a problem. Unlike other contaminants, such as metals, most volatile organic compounds do not occur in nature, so if they are detected, they are likely from the landfill. We suspect the contaminants found in this well may have been carried by landfill gas moving under the ground. Concentrations have dropped over the years, primarily because the owner has installed an extensive landfill gas removal system.
Low concentrations of volatile organic compounds have also been detected in other wells but subsequent sampling has not found the compounds in these wells. The permit requires that if a volatile organic compound is detected and is not due to sample handling or lab contamination, the well must be resampled to confirm the presence of that contaminant. Confirmation sampling has not shown the presence of volatile organic compounds in any of the wells, other than the one mentioned above.
DEQ officials inspect Riverbend Landfill in accordance with the facility's air, land and water quality permits.
Air quality inspection reports
The U.S. Environmental Protection Agency and the Title V operating permit program require that inspections of the facility occur at least every other year. Prior inspections of the facility have shown it to be in compliance with the Title V permit conditions. The inspection reports for 2010 and 2012 are found below:Solid Waste inspection reports
Water quality inspection reports
The NPDES 1200-Z General Stormwater Permit compliance can also be evaluated through an on site compliance inspection.
Nuisance odor investigation
The goal of DEQ’s Nuisance Odor Strategy is to resolve odor complaints with cooperative voluntary remedies instead of using enforcement actions to address the issue. DEQ staff identified possible violations at Riverbend Landfill and referred those violations to EPA for further investigation and potential enforcement action. In September 2021, EPA completed its investigation and enforcement action which resulted in a consent agreement between EPA and Riverbend Landfill and assessed a civil penalty of $104,482. Since enforcement action has been taken, use of the Nuisance Odor Strategy is no longer appropriate and the nuisance odor study has been closed.
Potential for migration of the South Yamhill River
Residents have expressed concern about the potential for the South Yamhill River to migrate over time, because it could therefore move closer to the landfill. This issue was evaluated in a September 2012 report by Waterways Consulting, Inc. The report concludes that the river has not migrated in this direction substantially in the past. Among the factors considered, the report points to the presence of 3,000-year-old Native American artifacts found in the land between the river and the landfill.
Landfill contours are documented using aerial photography every year.