Dehalococcoides, a little microorganism with a long name, will start breaking down a nearly two-mile long plume of a carcinogenic pollutant from downtown to the North Platte River this year.

For more than a century, an "orphan plume" of perchoroethylene (PCE) drifted from the area of the former Lobell Refinery -- in the vicinity of South Wolcott and South Center streets, and West Collins Drive -- and other businesses. It's an "orphan" because nobody knows for sure who's responsible for it.

The Wyoming Department of Environmental Quality began testing for PCE in 1989, and it took years to map its size and location, and issue reports: It cuts a 150-acre swath to the south by Yellowstone Highway, to the west by Elm Street, and to the east by Washington Street, and to the river on the north.

"Now we're in the stage of actually trying to clean it up," DEQ Project Manager Matt Buchholz said at an open house at the University of Wyoming Agricultural Extension Building on Tuesday.

"We're going to implement some remediation strategies, and try and knock down the plume," Buchholz said. "It's a carcinogen, so it's definitely serious."

The volatile organic compound PCE, used in drycleaning and cleaning tools, does not pose an immediate threat. But in 2009, the DEQ found about 10 houses along the plume with unsafe contamination levels, so it installed mitigation systems, he said.

In April, the DEQ and Geosyntec Consultants will go to work to bioremediate the area with the help of glorified vacuum cleaners to suck out perchloroethylene in soil vapor.

They'll also enlist the help of the bacterium, dehalococcoides, commonly used to break down the PCE, Buchholz said.

"We put vegetable oil in with those," he said. "You want a healthy population of bugs, so you give them a lot of food, a lot of nutrients, and help them thrive. And by them thriving you actually help them break down the PCE faster."

Dehalococcoides breaks down the carcinogenic PCE to harmless chemicals, Buchholz said.

The DEQ and Geosyntec Consultants hope to see a dramatic decline in the PCE over the next decade, he said.

This phase of the remediation will cost about $550,000, Buchholz said. The costs cover high-resolution site characterization efforts, implementation of soil vapor extraction and enhanced in-situ bioremediation remedies, and follow-up monitoring, he said.

Geosyntec Consultants environmental engineer Emily Stockwell said the PCE has settled into the soil and the ground water to the bedrock about 25 to 40 feet under the city.

"Nobody is drinking that ground water, so it's not going to present a hazard to everyday people in Casper," Stockwell said.

Work crews will install injection wells and other equipment on sidewalks and maybe streets starting in the source area of the plume and work toward the river, she said. "There might be a little bit of sidewalk closures and road closures, but not more than a couple of weeks worth."