A local environmental group on Wednesday filed a lawsuit seeking to overturn the South Coast Air Quality Management District’s recent approval of environmental reports for Tesoro Corp.’s plan to merge operations of its two refineries in Carson and Wilmington.

The expected lawsuit was filed in Los Angeles Superior Court by Communities for a Better Environment, a Huntington Park-based environmental justice group, which calls the merger an expansion that will import crude oil and add to the pollution burden borne by communities neighboring the two nearly-adjacent refinery complexes.

San Antonio-based Tesoro’s $460 million project would combine the operations of two refineries the company had purchased over the past 10 years from BP North America and Royal Dutch Shell, thereby creating the largest refinery on the West Coast. The AQMD approved the massive project’s environmental impact report last month.

Tesoro and project supporters in the business community say the project will modernize processing, safety and pollution control equipment at the refinery complex, allowing it to produce cleaner fuel more efficiently.

But Communities for a Better Environment and other community groups say the project’s main aim is to import “dirtier” crude oil from North Dakota’s Bakken oil field. They also note the region around Carson and Wilmington already has five refineries and thus suffers the disproportionate impacts of pollution from those refineries.

CBE alleges in the lawsuit that the air district failed to study the environmental impacts of such “dirtier” crude and other emissions from expanded operations at the merged refinery complex. The lawsuit seeks a court order to invalidate the air district’s approval of the environmental documents and conduct a new environmental review taking these factors into account.

“The District has a duty to investigate such projects with the utmost scrutiny, and we are very concerned that it dismissed evidence indicating that a core project purpose is to refine extreme, dangerous crudes, and also underestimated the project’s environmental impacts to communities already under siege by refineries and other polluting sources,” Gladys Limón, staff attorney with CBE, said in a statement.

The air district responded to the filing of the lawsuit in an emailed statement.

“Following extensive review and consideration of the document and comments received, SCAQMD’s executive officer certified the Tesoro EIR, recognizing the overall reduction in air pollution and reduced impacts to the neighboring community.”

On the dirtier crude oil issue, the air district response cited their response document to the environmental impact report: “The proposed project will not enable a change in crude oil processed.”

Public policy and energy reporter Howard Fine can be reached at hfine@labusinessjournal.com. Follow him on Twitter @howardafine.