A $48 million price tag for wastewater treatment upgrades kept Carson City’s Board of Supervisors Thursday pondering past problems and future possibilities. It prompted Mayor Robert Crowell to grouse about the past, all members to puzzle about future moves and everyone at the city’s capital budget preview meeting to ponder prospects for a 10 percent annual sewer rate hike over five years that Public Works Director Andy Burnham said may be recommended in April to do the job. The discussion, meanwhile, was merely the finale of a morning in which it became plain megabucks are needed for the city’s other …