Federal authorities are monitoring a natural gas leak at an offshore platform in the Gulf.  The Bureau of Ocean Energy Management says the platform is located about 93 miles south of Lake Charles in about 173 feet of water. Authorities say the platform has not been in production for nearly a decade — and currently is used to process natural gas and condensate from other offshore sites. Investigators say the leak was discovered Sunday when workers on an Apache Corp. crew spotted bubbling near the platform. The platform was evacuated and pipelines were cut off. The federal agency says Apache is using a robotic vehicle to see if the platform can be reboarded safely. If not, authorities say a relief well will be drilled.