delek us holdings inc reported an operational disruption and excessive gas emissions at its oil refinery in big spring texas a process unit upset resulted in exceeding the so2 sulfur dioxide 500 lbs per 24hr reportable quantity the west texas refinery said in a statement tuesday night to the texas commission on environmental quality operational moves were made to immediately minimize emissions delek said the emissions lasted about 16 hours on tuesday and affected units included a diesel hydrotreater and a fluid catalytic cracking unit the 73000barreladay big spring refinery is located in west texas 44 miles east of midland