Every weekday, about a dozen large garbage trucks peel away from the oil boom that has spread through western North Dakota to bump along a gravel road to the McKenzie County landfill.

The trucks drive up to a scale flanked by something seldom found in rural dumps — two 8-foot-tall yellow panels that essentially form a giant Geiger counter.

Two or three times a day, the radiation detector blares like a squad car, because under tons of refuse someone has stashed yard-long filters clotted with radioactive dirt from drilling sites.

The "socks" are supposed to be shipped to out-of-state processing plants. But some oil field operators, hoping to save tens of thousands of dollars, dump the socks in fields, abandoned buildings and landfills.

"It's a game of cat-and-mouse now," said Rick Schreiber, the landfill's director. "They put the sock in a bag inside a bag inside a bag."

Nearly 1,000 radioactive filters were found last year at the landfill, part of a growing tide of often toxic waste produced by the state's oil and gas rush. Oil field waste includes drill cuttings — rock and earth that come up a well bore — along with drilling fluids and wastewater laced with chemicals used in fracking.

To many local and tribal officials, environmentalists and some industry managers in North Dakota, the dumping of the socks and the proliferation of other waste shows the government falling short in safeguarding the environment against oil field pollution.