Well I hate to tell ya this, but as the other poster said there ain't no easy fix. What often happens is the septic tank gets over full with solids which then enter the leach field and clog the gravel/soil. Regular septic tank pumping evry few years is the best preventitive. Once clogged though, the leach field will need to be replaced. Pump the tank first, or else when you break the outlet pipe you'll have a raw sewage geyser, thats not pleasant. The new leach field can be close to the old one, best to ask a local engineer how/what/where to place it and how deep your soil conditions will allow the grave bed.
Its really not too bad and just amounts to some digging, drain rock (1 1/2" gravel) and some perforated 4" drain pipe (cheap) but you really should get directions from someone knowledgable and local. If no one knowledgabe is availabe, and your water table is low, say below 10', then you could just bootleg the new leach lines by digging a trench with 3'-4' below the pipe filled with gravel, be sure the new pipe has about 1/4 bubble fall, and then cover the new pipe with paper before backfilling. 80' of this should work just fine, of course its best to do it proper and get the permits and engineered design, this is just rule of thumb.