Perform your own assessment. Most septic systems are designed by specialists and the leach lines are placed in the optimum position. The leach field or drain field is placed where the soil is sandy enough to allow the effluent to drain within the required time. Setbacks from property boundaries, homes, wells (includes neighboring properties), bodies of water, and swampy or drainage areas must be observed. Measure the existing lines and measure the new proposed placement and determine whether they will be at a lower elevation from the septic tank and will fit in with the setback requirements.
Hire a septic engineer or certified installer if you believe the lines can be moved. Ask him to visit your property and confirm that it is possible to re-align your drain field. In many states a new septic system design must include a reserve area for a new leach field to be installed if the first one should fail. If the setback ordinances cause a problem with the existing leach field and you have a reserve area, you may be able to build a new leach field and redirect the leach lines.
Apply for a permit from your local health department. The application should be accompanied by a plan showing the location of the home, boundaries, drainages, water bodies, nearby wells, the existing leach field, and the proposed new location and direction of the lines. It can be hand drawn in most states. If you are moving your leach field, you may have to have soil tests performed by a certified septic technician prior to approval.
Excavate for the new lines. Dig the trenches following the local required specifications. They usually have to be at least 18 inches deep and must be lined with a specific size of gravel or filter fabric, and in some states a man-made PVC "vault." Dig out the existing pipes and install or re-align the distribution box. Place the old pipes in the new trenches, provided they are still in good condition, or use new pipes. Attach the pipes to the distribution box outlets. Call the health department inspector. Once he has approved the new drain field, you can cover it up and start using it.