Oregon State Police are investigating a serious-injury crash involving a semi-truck and passenger car on Interstate 84 near Arlington.  The crash happened Thursday morning at about 6:49, near milepost 137.  State Police say a Freightliner towing three trailers, driven by 32-year-old Edwin Alexander Gomez of Pasco, Washington, left the eastbound lanes for an unknown reason, crossed the median, and struck a westbound Ford Edge.  The Ford rolled over.  Its driver, 51-year-old Pratapa Reddy Koppula of West Hills, California, suffered minor injuries.  Gomez also suffered minor injuries.  A passenger in the semi, 26-year-old Ashleigh Darlene Krupkat of Kennewick, was seriously injured and taken to an area hospital.  Police arrested Gomez on suspicion of DUII, reckless driving, recklessly endangering another person, and fourth-degree assault.  Westbound I-84 was affected for about eight hours while crews handled hazardous materials, investigated the crash, recovered the vehicles, cleared debris, and repaired the median.