The H.W. Hill landfill gas power plant is located alongside the Roosevelt Regional Landfill. Away from sight and hearing of other land uses, the plant is able to generate electricity with no adverse environmental impacts and a notable positive impact -- generating green, renewable electricity.
Thousands of feet of perforated pipe is buried right in the landfill. Blowers create a vacuum on this pipe to draw out the landfill gas. Landfill gas is 55 percent methane and 45 percent carbon dioxide (plus trace other compounds). Methane is a destructive greenhouse gas, 20 times more destructive than carbon dioxide. Two million tons of waste produces enough methane to generate 1 megawatt of electricity.
	Before the power plant, the gas was "flared" to neutralize the greenhouse gases and VOCs (volatile organic compounds) and reduce odors. Today, most of the landfill gas goes through the power plant, although excess gas is still flared.
When the gas is delivered to the power plant, its first stop is a water knock-out tank. Condensation in the tank removes impurities from the gas, which prolongs engine life.
	The gas enters the Compression Building, where it is compressed from 1 psi (pound/square inch) to 65 psi.
Air coolers lower the temperature of the gas from 190 to 100 degrees. A refrigeration unit chills the gas to 40 degrees to allow more contaminants to fall out with condensation. The gas is then re-heated for its underground trip to the Generation Building.
	The Generation Building houses five Waukesha spark-ignited turbo-charged engines modified to run on methane. Each engine consumes about 10,000 BTUs and 18 cubic feet of gas to produce each kilowatt hour of electricity.
A generator is mounted on the end of each engine. Each engine-generator set produces 2.1 megawatts of electricity, or 50,000 kilowatt hours per day. During the plant's first year of operation, with four engines in place, it generated 66 million kilowatt hours of electricity. That is enough power to serve 4,500 homes.
	Like over-sized car or truck engines, the power plant's engines produce exhaust and excess heat. Behind the Generation Building mufflers reduce engine noise and radiators cool intake air after it is turbo-charged and before it enters the engines. The plant exhausts pollutants equal to 100 cars driving down the highway.
A new substation steps the generation voltage (4,160 volts) to 69 kv. The substation is integrated into the PUD's SCADA system to track generation and provide alarms for engine problems. The substation is large enough to handle 12 engines, or power to serve 15,000 homes.
	Six miles of new transmission line connect the plant with the PUD's transmission system at Roosevelt. The power's first customers were Snohomish PUD (5 mw), Goldendale Aluminum Co. (1 mw), Benton PUD (1 mw) and Clallam PUD (1 mw).