Tar sands refining in Southern California needs scrutiny, say environmentalists

Oil refiners are sending greater amounts of an especially dirty crude oil product called “tar sands” to their Southern California refineries.

Now environmental groups want regulators to take a closer look

Tar sands hold a kind of semi-solid petroleum. To refine it enough for California standards takes more processing. Oil companies – including Valero, Tesoro and Conoco Phillips – say they’re bringing in more of this raw material because liquid petroleum in California is drying up.