A propane leak at a Grass Valley supplier’s station prompted evacuations amid concerns  of combustion Thursday morning. Shortly before 8 a.m., a caller on scene reported an explosion, according to dispatch logs provided by the Grass Valley Police Department. That report proved to be inaccurate, said Mark Buttron, a battalion chief with Grass Valley Fire Department. Units arrived to find  no fire or explosion on the 13000 block of Grass Valley Avenue. Responders included four engines and two battalion chiefs. Approximately 25 gallons of liquid LPG turned to vapor following a transfer failure from supply truck to storage tanks. Internal …