Greener grass over a drainfield generally indicates that the absorption of water is slow and the water cannot drain into the ground and thus comes toward the surface.  This is the sign of a drainfield heading toward failure.  

The smell from the garbage disposal when doing laundry is probably due the rising water levels in the septic tank which forces some of the gases back up the plumbing system.  If this is the case, then the garbage disposal is the path of least resistence to letting these gases escape.  

You may be able to treat your system with Septic-Scrub.  If you would like to discuss your situation in more detail, please do not hesitate to call.