General Motors Corp. expects to shell out about $704 million this year to clean up sites designated as environmentally polluted by the Environmental Protection Agency and state regulatory agencies, says the automaker's 10-K. The report also shows that GM will just miss the required Corporate Average Fuel Economy numbers for 1995. For cars it's projected at 27.4 mpg -- the requirement is 27.5 mpg. The fleet average for trucks this year will be 20 mpg; the requirement is 20.6 mpg. The shortfalls will be offset partially by credits earned in future model years.