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Polk County resource‑recovery facility reports dioxin exceedance on Unit 2; board approves retest and engineering run
Summary
County staff told commissioners that the facility’s Unit 2 exceeded a federal dioxin‑furan standard on one run during a recent required stack test. The board authorized a $26,685 testing and engineering contract and staff said a retest is already underway.
Polk County staff told commissioners on July 2 that a recent three‑year stack test at the county’s resource‑recovery facility recorded a dioxin‑furan spike on Unit 2 that exceeded the federal limit on the averaged result from three test runs.
The county’s testing firm returned laboratory results showing Unit 1 met limits and Unit 2 had two acceptable runs followed by a third “spike” that pushed the averaged value over the federal threshold. County staff said they filed a notice of deviation with state regulators and have been negotiating with the Minnesota Pollution Control Agency (MPCA).
“Unit 2, the first two runs looked very good. And the third one, we hit something in there and it spiked badly. It spiked about three times higher than our historic spikes during the test,” county staff said during the meeting. Staff described the likely cause as material in the fuel stream — an intermittent, unobservable contaminant such as PVC or another chloride source — rather than a mechanical failure of the combustion unit.
County staff noted the federal dioxin‑furan limit referenced in the meeting material is 125 nanograms (average) whereas the state standard cited is 500 nanograms. Staff said the spike moved Unit 2 above the federal limit on the average that counts for federal reporting.
To address the exceedance and better understand formation conditions, commissioners approved a $26,685 vendor quote that covers additional full stack testing plus an engineering run to test a lower temperature set point into the electrostatic precipitator (ESP). The vendor also proposed an hourly rate for any extra time should tests need to be extended because of equipment or sampling delays.
Staff said the initial notice and failed run were not apparently caused by a mechanical breakdown: “We’re unaware of any breakdown. The units, everything in the unit performed flawlessly…We believe it was something in the fuel…which makes it really hard to make any adjustment going forward,” staff said.
A retest schedule was described as already underway: staff said they began follow‑up testing immediately and expected to complete remaining runs in a matter of days, with laboratory analysis taking approximately two months. The county also reported that a grant‑funded bag‑opener project due in September should reduce the potential for large bags and contaminants entering the combustion stream in the future.
The board’s approval authorizes tests and the engineering run; staff said they will continue to work with the MPCA on possible noncompliance findings and any related fines, and will brief the board when final laboratory results arrive.
The county emphasized that the engineering run aims to evaluate whether slightly lower ESP inlet temperatures move the operating range away from the temperature window where dioxin formation is more likely to occur.
