By Nicole Montesano • Staff Writer • 

Landfill leachate report on tonight's agenda

The Yamhill County Solid Waste Advisory Committee met Jan. 20 to discuss a report suggesting leachate may be escaping from portions of the Riverbend Landfill pre-dating the requirement for modern liners.

The landfill is required to collect all liquid that leaches from the landfill and dispose of it as hazardous waste. It has installed a system of collection pipes to move leachate to a holding pond, pending trucking offsite for disposal.

However, the Stop the Dump Coalition, formed to oppose expansion of the local landfill operation, commissioned a report suggesting leachate is slipping through. It was compiled by Mark Yinger, a professional landfill hydrologist.

The review comes against a backdrop of continued infighting over a proposed landfill expansion.

Last year, the county commissioners approved an expansion designed to enable the rapidly filling landfill to continue operating. However, the decision was remanded for reconsideration in November by the state Land Use Board of Appeals.

LUBA ruled the county erred in determining the landfill did not have a significant impact on local farmers. The county has not yet taken any action in response.

Yinger reviewed the landfill’s 2013 and 2014 Annual Environmental Monitoring Reports, its 2007 and 2013 Environmental Monitoring Plans, a 1993 remedial investigation report and test results from the landfill’s monitoring wells. He said they show the monitoring wells have been detecting increasing contamination in landfill leachate and suggest strongly that some of that leachate is escaping from the site.

Yinger said the leakage is coming from the oldest cells at the landfill, which are lined only with compacted soil. At monitoring well 5A, located down-gradient from the landfill in a shallow aquifer, three volatile organic compounds were detected in 2013 and 2014 — chlorobenzene, 1,4-dichlorobenzene and cis-1,2-dichloroethene.

“These three VOCs have consistently been detected at MW-5A, starting as early as 1992, when the well was installed,” he said. “From 1992 through 2014, the concentrations of chlorobenzene and 1,4-dichlorobenzene have not decreased, but have in fact at times increased. ... Landfill gas extraction, which began in 1997, has not reduced the concentration of chlorobenzene and 1,4-dichlorobenzene in groundwater at MW-5A.”

He went on, “At MW-5A, the concentration of the leachate indicators sodium and magnesium are statistically elevated with respect to background water quality. The concentrations of sodium and magnesium detected in water samples collected from MW-5A in 2013 exceed the UPLs ... This indicates that groundwater at MW-5A is impacted by leachate from the landfill.”

Although newer parts of the landfill include leachate collection systems designed to prevent off-site migration, the remedial investigation report indicates there is no collection system at the base of Cell 1 because that cell had been partially filled when the landfill began installing the system. “Because the bottom of Cell 1 is beneath the water table, and there is no leachate collection sump at the base of Cell 1, it is reasonable to conclude that the bottom of Cell 1 is saturated with leachate that cannot be recovered,” he wrote.

Yinger indicated in the report, “There are statistically significant upward trends in the concentrations of bicarbonate alkalinity and magnesium in groundwater.”

These increasing trends were not reported in the 2014 Annual Monitoring Repport, he said, because “detection well MW-5A is not included in Table 6-3 ... as it should have been. If MW-5A had been included ... , it would have shown that the concentrations of leachate indicators are increasing.”

Yinger said that concentrations of sodium and magnesium also are increasing at the next well down from MW-5A, which is MW-12A. He said the annual environmental monitoring reports failed to show, but should have shown, “increasing trends for chloride and total dissolved solids at MW-12A, in addition to the increasing trends of bicarbonate alkalinity, calcium, magnesium, nitrate and sodium.”

Those weren’t the only lapses in the report, Yinger said.

“Other statistically significant increasing trends were not identified (either),” he said. “At compliance well MW-14A, the concentration of magnesium is increasing. At compliance monitoring well MW-16A, sulfate is increasing. At compliance well MW- 21A, ammonia as nitrogen is increasing.”

As a result, Yinger concluded, “Prior to further consideration of a permit to expand (the landfill), the DEQ should require a remedial investigation into the release of leachate from the older unlined landfill cells.”


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