Breaking rock with a rotary hammer
This is an old question but I will answer it for any who land here.  This job is probably too large for chipping with a rotary hammer, but that depends on the toughness of the rock.  

Renting a diesel compressor, 2" rock drill and rock splitter would solve this problem quickly.  Another solution if a rock splitter is unavailable or too expensive is to use an expanding rock splitting grout such as Apex Nexpro, Ecobust or Dexpan.  The grout is pored as a liquid into a pattern of drilled holes, and expands with massive force as it cures, destroying rock or concrete non-explosively.