ExxonMobil Corp. has started mixing petroleum-derived and renewable diesel fuels together here at its first biodiesel blending project in the U.S., says the Irving, Texas-based oil giant.

The $3.1 million blending operation, located at ExxonMobil's 15-acre Spokane Terminal, at 6311 E. Sharp, in Spokane Valley, was constructed in response to a 2006 Washington state law that required 2 percent of diesel fuel an oil company sells in the state be biodiesel, says Patricia Errico, a spokeswoman for ExxonMobil.

The law, which went into effect Nov. 30, is somewhat symbolic, because it doesn't identify an enforcement authority, says Peter Moulton, the state's Olympia-based bioenergy coordinator.

Moulton says, however, that other petroleum terminals in Seattle and Portland, Ore., also plan to install biodiesel-blending equipment.

Biodiesel is a nonpetroleum diesel fuel produced from renewable sources. Most biodiesel produced in the U.S. is derived from soybeans, Errico says. Other sources of biodiesel include canola seed, palm oil, and recycled cooking oil.

Biodiesel can be mixed at any ratio with petroleum diesel to create a biodiesel blend, although some vehicle manufacturers don't recommend blends that contain more than 5 percent biodiesel, also known as B5, she says.

Exxon Mobil's Spokane Terminal biodiesel-blending project included installation of valves, pipes, pumps, and related equipment that ensures precisely controlled blending of biodiesel at an area of the terminal where tanker trucks are loaded with fuel for delivery to service stations, Errico says. A pump system allows both biodiesel and petroleum diesel to enter simultaneously the overhead pipe—called the loading arm—that fills the delivery trucks.

She declines to name the contractor on the project, but says a work force and vendors for the contractor were selected from the Inland Northwest and surrounding areas.

Records on file with the city of Spokane Valley list SPEC Consulting LLC, of Albany, N.Y., as the engineer on the project.

ExxonMobil's Spokane Terminal is supplied with conventional fuel via the Yellowstone Pipeline, which transports petroleum products between Billings, Mont., and Moses Lake, Wash. Moulton says most other forms of diesel fuel are made in the Midwest and will be transported to the terminal via rail and trucks.

The terminal employs six full-time workers, and fuel is delivered from there to service stations in Central Washington to western Montana, she says.

ExxonMobil declines to disclose how blending will affect the cost of diesel.

Two years ago, the rule of thumb was that a B5 blend cost 5 cents more a gallon to produce than conventional diesel, Moulton says. Following recent fluctuations in both petroleum and commodity prices, "that rule may be out the window," he adds.