Valero Energy reported a first-quarter loss compared with a year-ago profit on Thursday, weighed down by lower refining margins and around $1 billion in impairment charges related to its West Coast assets.

The San Antonio company says it’s intent on shuttering a major California refinery on the heels of refining losses of $530 million so far this year.

Valero approved plans to either idle, restructure or shut down the Benicia refinery following concerns over California's dwindling fuel supplies and soaring gasoline prices.