On February 10, 2014, landfill personnel observed leachate escaping from the landfill’s northern boundary. Waste Management reported that this leachate reached a creek approximately 300 feet from the landfill. This leachate was primarily liquid that had collected in the landfill’s gas extraction wells. To keep the extraction wells working properly, this leachate is routinely pumped from the wells to three 22,000-gallon storage tanks near the north side of the landfill. This leachate is kept separate from the majority of the landfill’s leachate, which is pumped to the onsite leachate pond. This reason for this separation is that leachate associated with the gas extraction wells is more concentrated than the rest of the landfill leachate, and is therefore sent to a different offsite facility for treatment and disposal. Tanker trucks that routinely haul this leachate to an offsite treatment plant were unable to get to the site because of heavy snow and icy roads. Flow of leachate from the landfill to the tanks was stopped because the tanks were full. This is believed to be the reason leachate began seeping from the landfill. To prevent this problem in the future, Waste Management has connected these tanks to the pipeline leading to the onsite leachate storage pond.
Impacts to the creek were evaluated in a March 13, 2014 report prepared by Waste Management’s consultant, CH2M HILL. The CH2M HILL’s report concludes that “No mortality of aquatic flora or fauna was observed during either site visit [conducted on February 12 and 21, 2014]. Overall, the impact to aquatic biota was estimated to be minimal on the basis of the high flows of the unnamed creek and the South Yamhill River, and the comparison to aquatic water quality criteria and human health criteria.”
DEQ inspected the site on February 12, 2014. View the inspection report, along with photographs. DEQ concurs with the findings of the consultant's report. However, in light of the release of leachate to the creek, DEQ is pursuing enforcement action against the landfill.
Another consultant for Waste Management, SCS Engineers, sampled soil in the area between the landfill and the creek through which the leachate traveled. View the results of the SCS study.
A previous seep was found on January 28, 2014, approximately 400 feet west of the February 10 seep. This leachate migrated beyond the perimeter of the landfill, but did not travel far from the landfill perimeter. This release was from an old perimeter French drain that was clogged as the result of recent construction of a stormwater diversion swale. The drain had been installed during construction of the landfill cell to convey leachate to the leachate collection line that runs to the onsite leachate storage pond. To address this problem, the landfill contractor removed all drain rock from the French drain along that portion beneath the stormwater diversion berm. Between January 28 and 29, this rock was removed and the area was backfilled with compacted clay. Four vertical 12-inch sump pipes were installed and backfilled with drain rock. Soil from the impacted area north of the landfill was sampled on January 29. Soil impacted by the leachate release was then excavated, and a vacuum truck was used to remove standing stormwater that may have been contaminated by the release. Soil from this area was resampled on January 31. Results were provided in a technical memorandum dated March 14, 2014, prepared by SCS Engineers. These results indicate that residual contaminant concentrations are below safe levels.
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.
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.
Closure and post-closure financing
Landfills are required to set aside funds sufficient for proper closure of the landfill and 30 years of post-closure maintenance and monitoring. Estimates of the necessary funding must be revised every year.
Financial assurance documents: