On its face, Oregon’s low-carbon fuel standard has a simple promise: it will reduce carbon emissions from transportation fuel used in the state by 10 percent over a decade, starting in 2016.

As it turns out, even supporters of the underlying law disagree over how the state should calculate that reduction. The standard is supposed to account for the total amount of carbon generated by gas, ethanol, electricity and other fuels across their life cycles, from the field or power plant to the tailpipe.

Fuel importers and producers will likely meet the standards through a combination of cleaner biofuels blended into gas and diesel, as well as carbon reduction credits the state will issue to owners of electric charging stations and other alternative fuel infrastructure.

The Oregon Department of Environmental Quality proposed rules last month that would follow California’s lead to include the impact of new demand for biofuels crops such as corn and soybeans. This factor is known as the indirect land-use change and as recently as January, Department of Environmental Quality staff said existing methodologies were inadequate to calculate it. However, Cory-Ann Wind, an air quality manager for the Department of Environmental Quality who works on implementation of the low-carbon fuels program, said on Oct. 14 that California recently updated the models it uses to calculate the carbon impact of land-use changes, based on extensive peer-reviewed research.

“I feel very comfortable with the work they’ve done to develop the most recent of their numbers, and that’s why we recommended including the California (carbon intensity) values into the Oregon program,” Wind said.

The deadline to submit comments on the latest proposed fuel standard rules is 4 p.m. Oct. 21. As of Thursday afternoon, no one had submitted comments on the rules.

California used two models to estimate land-use impacts: one is an economic model that calculates the impact of fuel policy on agricultural and other real estate prices, and the other quantifies the amount of carbon emissions that occurs when land is converted to grow biofuel feedstock. The carbon impact occurs when land where carbon was sequestered, such as a forest, is converted to farmland.

Geoff Cooper is senior vice president at the Renewable Fuels Association, a national ethanol industry group with offices in Washington, D.C. and St. Louis. Last month, Cooper told The Oregonian that if Oregon adopts the indirect land-use change model to calculate carbon emissions, the ethanol group will work with the petroleum industry to repeal the low-carbon fuel standard.

“They’re saying, ‘Well, land we use for soybeans and pasture here is now being used to grow corn for ethanol so a farmer somewhere else in the world now has to convert some land to make up for that lost soybean pasture here,” Cooper said on Oct. 14. “The real world data is showing that isn’t happening.”

Wind disagreed and said “satellite data for land use conversion now is great.”

The Department of Environmental Quality proposal would attribute a greater carbon impact to corn ethanol compared with existing rules, and Cooper said corn ethanol refineries such as Pacific Ethanol, Inc. in Boardman would face reduced demand from companies that import gas into the state.

“If you look at the ethanol that’s used in the state of Oregon today, it’s primarily corn-based ethanol produced at a facility there in Boardman, as well as facilities elsewhere in the United States,” Cooper said. Cooper said if Oregon is going to include the indirect land-use impact, it should rely on modeling by researchers at the U.S. Department of Energy’s Argonne National Laboratory in Illinois, rather than models from California.

Two other groups that pushed for lawmakers to make the low-carbon fuel standard permanent are supportive of the state’s proposal to include land-use impacts in carbon values.

“These measures of overall carbon pollution are the result of years of input from numerous businesses, organizations and scientific experts,” Oregon Environmental Council communications director Jessica Moskovitz wrote in an email. Moskovitz said the models the environmental agency plans to use are “the most accurate and honest way to assess the carbon pollution of transportation fuels.”

Kristen Sheeran, Oregon director for Climate Solutions, wrote in an email that one reason the group supports the low-carbon fuel standard is the “incentives it provides to grow clean fuels markets in our region.” Climate Solutions is a nonprofit with offices in Oregon and Washington that promotes renewable energy and other policies to address global warming.

“The Clean Fuels Program is an important part of Oregon’s plan to meet its legislated greenhouse gas reduction targets,” Sheeran wrote. “The program is designed to reward the cleanest fuels. For this reason, it is important to consider the full life cycle of carbon impacts of fuels in the program.”

Wind said the inclusion of the indirect land-use impact is not the only change in the latest proposed rules to implement the fuel standard. The Department of Environmental Quality also wants to update the carbon value for natural gas, because of new research that shows more “fugitive methane” escaping from fracked wells.

And although palm oil cannot currently be used to meet Oregon’s existing renewable fuel mandate, which calls for 10 percent ethanol blended into gasoline and a 5 percent biodiesel blend for diesel, Wind said there are ongoing discussions about whether Oregon should allow biodiesel palm oil if it comes from certified sustainable plantations. Palm farmers have cleared large areas of tropical rainforest, and smoke from fires used to clear forests in Indonesia has caused health concerns even in neighboring countries in Southeast Asia.

There is a public hearing on the proposed rules 9:30 a.m. Monday, at DEQ Headquarters in Portland, on the 10th floor of 811 Southwest Sixth Avenue. People can also submit comments online at www.oregon.gov/deq/RulesandRegulations/Pages/comments/Ccleanfuelsupdate.aspx.