Methane gas
A man unloads his garbage at the Tangerine Landfill early last year. The landfill could soon generate 1,400 kilowatts of electricity each hour from methane gas. Explorer file photo

If all goes according to plan, by the summer of 2012, Pima County’s Tangerine Landfill will be generating 1,400 kilowatts of electricity an hour from methane gas trapped under its 80 acres.

Pima County has signed a contract with Sexton Energy of Bannockburn, Ill., to install a methane gas collection system and turn the collected gas into energy that would be fed into Tucson Electric Power grid.

“The good thing about the contract is that there is no risk to the county,” said Ursula Kramer, director of the county’s Department of Environmental Quality. “The contractor is paying for all of the installation and will operate the equipment at the landfill. And if they find that they are not able to extract enough methane gas to generate power, the county will not have lost anything because no taxpayer money is at risk.”

Pima County would receive a royalty of 1 percent of the gross revenue that Sexton Energy makes from the power generation, she noted.

Mike Carolan, Sexton Energy’s owner, said his firm has an agreement with TEP to purchase energy produced by the operation and currently is working to get an interconnection agreement with TEP to tie into the electric grid.

Carolan said the program should qualify for the state’s Renewable Energy Standards Tariff program, which encourages utilities to use renewable sources of energy to generate power. He said a probe well will be drilled soon to get a sample of the gas in order to determine its quality. He added he expects the quality to be good, which would be consistent with typical landfills.

“We’ll drill 30 to 40 feet with a two-inch diameter probe to capture the gas,” he said.

Once the methane quality is verified, Sexton Energy will drill approximately 60 wells over the 80-acre landfill. Wells will vary in depth depending on their location, Carolan noted, because the landfill is deeper in the center than on its ends.

“Wells typically are drilled to about 10 feet above the bottom of the landfill,” he said. “We don’t want to pierce the liner, so we stay well above the bottom.”

After the wells are drilled, valves on top of the wells will be connected to a series of lateral pipes that connect to a blower, which produces a vacuum in the well pipes to bring up the methane. The blower then will direct the methane into another series of pipes to an engine that turns a generator, producing electricity. The generator would be connected to the TEP electric grid.

Carolan said the project cost is estimated at $4 million and the contract term is 15 years.

Kramer pointed out that the Tangerine Landfill is the only county landfill large enough to produce enough gas for such a project. The others—Ina Road (temporarily closed), Ajo and Sahuarita landfills—are too small.

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