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The Billings Regional Landfill will soon be more than just a graveyard for potato peels, lawn clippings and old Christmas cards.

For 40 years, the landfill just south of Billings has been accepting truckloads of garbage. Last year, about 250,000 tons of garbage made the one-way trip into the landfill, with little to show for it but flocks of birds drawn by the odor. But the trash is about to start giving back.

The bugs and microbes that break down the garbage over time give off methane, or natural gas. With the rush to find alternative energy sources and the need to control methane emissions from the landfill, city officials recently teamed up with Montana-Dakota Utilities to trap the gas before it escapes into the air above or the water below.

MDU has drilled three test wells at the landfill and is monitoring the mix of gases brought to the surface. If the test wells confirm that methane extraction is a good idea, and most involved are convinced that it is, about 40 more wells will be drilled.

Both sides are thrilled with the agreement, as MDU can process and sell the gas to its customers and the city can turn a potentially expensive problem into a steady source of new revenue. Faced with government requirements to prevent methane emissions at landfills, other cities often burn off the gas or use it to generate electricity. Foreseeing this problem, city officials had saved $725,000 to deal with the methane, but they can now use that money elsewhere.

The contract is for 40 years, with automatic renewal every 10 years unless either side wants changes. The city will receive 15 percent of the net gas sales, and unless gas prices collapse unexpectedly, MDU estimates that the city will see an average return of at least $500,000 a year. That means a windfall of at least $20 million over 40 years for something that could have cost the city money.

For an upfront investment estimated at $8 million and annual operating costs of $600,000, MDU could easily earn more than $130 million over 40 years.

Layers of the past

Earlier this month, a specialized three-man crew from Terra Engineering in Madison, Wis., drilled holes 3 feet in diameter into the garbage in three areas of the landfill. At the first hole, using a telescoping drill rig with a massive inverted bucket manufactured in Italy, driller Chip Freshcorn brought up a giant pile of garbage, or what was left of it after decades underground.

Then his partner, Tony Gilbertson, dropped in a perforated pipe and loose rock around the pipe. Gilbertson and Freshcorn have visited landfills across the country with their drill, and they have plenty of business these days.

An engineer, Matt Anderson, then capped the holes with a wellhead and a vacuum system that sucks the gas into the pipe. Anderson works for Wenck Associates, the company hired by MDU for the technical parts of the project.

On a cold windy Wednesday, the day after Election Day, it still helped to stand upwind from the drilling. In the first few feet of drilling, the garbage was fresh and newsprint was still clean enough to read.

At first, Freshcorn's drill brought up detritus of American life circa 2006: Taco Bell bags, old tires, junk mail and lots of plastic bags. Looking down into the hole was like looking into the past, with a yellowed bale of hay on one side and a Guinness beer six-pack carton on another. There were plastic bags all around, shredded as fine as hair.

Farther down, the fresh, intact waste turned to brownish sludge, followed by jet-black dirt. Finally, at 118 feet, the drill brought up what looked like topsoil. The crew had drilled far enough. The unearthed garbage revealed nothing too exciting, although Gilbertson and Freshcorn have stories from other landfills, like when they came across an equipment burial ground near a naval base.

"He drilled through a submarine in Seattle," Gilbertson said as he pointed to Freshcorn. "They cut it up in four pieces, and he ended up hitting one of them."

After the Terra crew left the first hole, Anderson looked into the deep blackness and explained that, as garbage decomposes, oxygen disappears. For the first few years of decomposition, the oxygen is slowly used up. Once it's gone, the army of microbes that take over begin pumping out methane. The microbes digest the organic material, which contains carbon, so food and paper and natural material goes quickly. Plastics and other manmade garbage - such as a chunk of submarine - will take much longer to decompose.

Anderson, standing on an iron grid placed over the hole, said the crews who do this work must be careful not to slip.

"If the fall doesn't kill you, the methane will," Anderson said. "There's no air down there."

Warming

Methane is a greenhouse gas, which means that as it rises into the atmosphere, traps heat and contributes to global warming. According to the Environmental Protection Agency, methane is about 20 times as potent as carbon dioxide as a greenhouse gas, so methane is regulated more tightly.

The methane, which is odorless until gas companies add that rotten-egg smell later, makes up about 50 percent of the gas pumped from below. Carbon dioxide makes up another 47 percent, with other gases such as hydrogen sulfide making up the rest. Hydrogen sulfide is the nauseating gas that gives rotten garbage its smell.

After a few days of testing, Anderson said, methane levels had dropped to about 51 percent, right where they should be. Oxygen made up less than 1 percent of the gas, and carbon dioxide made up most of the rest. The temperature of the gas mix was 70 degrees, which indicates busy microbes deep below the surface.

Methane production in landfills looks like a bell curve: It builds slowly, has a long plateau and then slowly declines as garbage decomposes. But the 200-acre Billings landfill has room to expand four times over, as the city owns about 800 acres in the area. Methane production will continue as long as it remains a landfill.

Every landfill is different, depending on moisture levels and age. More water in the garbage means more methane, while dry landfills can preserve garbage for centuries. Rick Thompson, the head of the solid-waste section at the Montana Department of Environmental Quality, said there are small dumps in the Helena area from a century ago that contain readable newspapers. Some landfills inject water to boost methane output.

In another part of the Billings landfill, Anderson said, the Terra crew had reached 40 feet in depth and was bringing up paperwork from the 2000 U.S. Census.

The DEQ monitors landfills in Montana for air and groundwater quality. Eventually, all landfills are required to do something about their methane, Thompson said. Methane escapes into the air through the soil, and it can leach into groundwater, which is why new landfills are required to install a lining before dumping garbage.

"As part of general landfill compliance, they submit methane levels on a monthly basis," Thompson said. "They go in and test, primarily to make sure gas at the property boundary is below the explosive limit."

Methane levels near the edge of the landfill can't be more than 5 percent of the explosive limit, which is the concentration that can cause an explosion when methane and oxygen find an ignition source. Because there's little oxygen in the garbage underground, explosions don't often happen at landfills.

Air quality and groundwater regulations are involved, too. The air quality regulations restrict the amount of non-methane organic gases, called NMOCs.

Once a landfill emits 50 metric tons of NMOCs into the air each year, the DEQ requires mitigation. The Billings landfill emits about 30 tons of NMOCs a year; city officials think they'll hit 50 tons in about 12 years.

"It's part of the cost of running a landfill. It's almost inherent," Thompson said. "It's easier to get rid of gas than to clean up groundwater."

Many landfills drill wells and install pipelines to collect the gas so it can be burned off or converted to electricity in gas generators. The Environmental Protection Agency estimates that two-thirds of landfills that collect methane convert it to electricity. Others use it to power city vehicles.

The landfill in Missoula ships its gas to a nearby factory, which uses it to heat the building. In Flathead County, the gas is burned for electricity and sold to an electric co-op.

Selling the gas directly to consumers is a newer concept that other communities are watching, said Barb Butler, the environmental compliance officer for the Billings landfill.

"The Solid Waste Division has been putting money aside. I've been here 14 years, and we've been putting money aside knowing that the day would come when we'd have to build a gas collection system," Butler said. "It was just a matter of time. So MDU sort of came in from the side and said, 'We'll build your gas collection system because we want to make some money.' "

The future

It's almost certain that the Billings landfill produces enough methane to make this collection project feasible. Engineers from Wenck Associates did a study last December that said the landfill could produce 1,480 cubic feet per minute of methane.

"It's 200 homes' worth of heat for 45 years," said David Hood, MDU gas superintendent.

But it will be close to two years before MDU drills the remaining 40 wells throughout the landfill. Over the next two years, the company will monitor methane output in the three test wells, which are hooked up to vacuums run by generators. Marlon Mackowick, an engineer with Wenck Associates, said engineers will visit the wells periodically to test the gas. Samples are collected in steel canisters and sent to a lab for analysis.

If MDU decides to go ahead with the project, it will drill more wells and install a piping system to move the gas to a collection point, probably somewhere on the landfill property. The collection point will be a building that contains a big vacuum system to draw in the gas, as well as a pumping system to send it into the consumer gas pipeline.

Once the raw gas reaches the landfill collection point, water and carbon dioxide are removed and the gas is cleaned of impurities. MDU will chill the gas and compress it before sending it out to customers.

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