The 362 MW Potrero Generating Station--long the subject of concern about air pollution in San Francisco--can finally close down at the stroke of midnight on February 28. The plant\u2019s owner, GenOn, can shutter the more-than-35-year-old plant under final regulatory clearance the California Public Utilities Commission granted Feb. 24 with no comment. GenOn, and its predecessor Mirant, have operated the plant under a reliability must-run contract with the California Independent System Operator for years to provide San Francisco with power. The plant was necessary, the grid operator maintained, because transmission capacity into San Francisco was insufficient to meet all of the city\u2019s power needs. That changed late last year with commercial operation of the 230 kV Trans Bay Cable. The new underwater line delivers up to 400 MW of power from several generating plants on the east side of San Francisco Bay to the city--eliminating the \u201cmust run\u201d back up by Potrero. CPUC approval for the closure came after the grid operator notified GenOn Jan. 1 that it was terminating its reliability contract with GenOn effective at the end of this month. The Federal Energy Regulatory Commission approved the termination later in January. Since the termination, the grid operator has not dispatched the Potrero plant, according to the CPUC. Closure of the plant addresses long-held grievances about air pollution in the surrounding Potrero Hill and Hunters Point neighborhoods. It also reduces stress on natural gas pipelines serving the city by eliminating a major use of gas in the area. Potrero consists of four generating units. The first--built in 1965--is a conventional fossil-fueled boiler driven steam turbine with a generating capacity of 206 MW. The plant also has three peaker units consisting of simple cycle combustion turbines, each with a capacity of 52 MW. They began operating in 1976.