Filters used to strain wastewater from oil wells that test positive for low-level radiation are being rejected at municipal landfills in the oil patch.

Williston landfill operator Brad Septka said since June he's rejected 23 oilfield loads that set off the landfill's Geiger counter.

Septka said the filters as well as the empty bags used to haul fracture treatment sand set off the counter.

Radioactive waste is regulated by the North Dakota Health Department. Scott Radig, who manages the state's solid waste program, said radioactive waste that exceeds the allowable level is supposed to be shipped to Colorado, where there's an approved disposal facility.

Radig said the detectors also are used at municipal landfills in Dickinson and in McKenzie County, as well as at four special waste facilities. He said operators there also have turned away loads.

He said the state's acceptable level for radioactivity is one of the lowest in the country, so low it can be found in some soils near where uranium and other radioactive materials occur naturally.

The radioactivity is showing up on tubular filters used to strain wastewater from oil wells before it's injected into deep disposal wells. There are hundreds of such disposal wells in the oil patch, where oil field fluids like the salty water that comes up with oil and fracture treatment water are injected.

Septka said he doesn't know where the rejected loads are going and Radig said the state doesn't have a manifest or tracking system to follow those truck loads.

"The waste generator can either take it and have it analyzed, or he can send it out of state," Radig said. He said the detectors used at Williston indicate that the radioactivity coming off the load is two times the normal background for radiation, not whether it exceeds the state's allowable level.

The department plans to meet with landfill operators in Williston next week to teach them more about the state's guidelines.

"We're getting started. Like so much in the oil field, this is catching us a little off guard," Radig said.

Some of the sand used in fracture treating oil wells also contains trace amounts of radiation, particularly the fracking sand from China made from aluminum oxide ore, he said.

Radig said Williston collected samples of various fracking sands and other oilfield materials for analysis to learn more about its radioactive content.

Radig said he isn't concerned about radiation in frack sand.

"Frankly, if it's two miles below the surface, it's not going to hurt a thing. There's no health risk that we can see," he said.

He said bottom sludge from oil tanks and scale from oil pipe also are sources of low-level radioactivity.

Reach reporter Lauren Donovan at 220-5511 or lauren@westriv.com.

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