uplumb, you can either ask someone from your local Department of Health to inspect it or ask them for a list of licensed people in your area who are able to inspect it and repair or replace it if necessary.
The field will probably have to be dug up at least partially to assess if it is at the proper incline and such.
It is likely that you will have to do a percolation test in your field to see how sufficiently it drains water. The exact requirements of the test depend on your location. When I had mine done, I had to dig four holes at least 8" wide and 24" deep and dump 5 gallon buckets of water in the day before the inspector (from health department) came out. He checked to see the water level and had me keep full 5 gallon buckets next to each hole so that he could dump the water in and then check the levels an hour later.
My drainfield was not done properly in the first place and had to be replaced (as did my septic tank since it was designed for a one bedroom house and we have a 3 bedroom house). We had old pipes with holes in them that were supposed to be over some sort of gravel but there was no gravel. The slope was too steep and the pipe (since there was only one of them) was too long. It was over 200' and its not supposed to be more than 100' per line.
Any work you have done on the field line is supposed to be inspected by someone from the Health Department. I believe you need a permit from the Department of Health as well. In my area the permit was free, but we could not get anything done until we had it. So basically you have to have the person doing the work talk to health department and they are supposed to supply a detailed sketch of what they plan to do for approval. Once approved the health inspector will issue the permit and allow the work to go on. Before it can all be buried, the inspector has to come out and look at the hookups and the depth of the lines and make sure that everything is right. It has to be the right incline and such.
Note: Your local dept of health might go by a different name. It might be Dept. of Sanitation, Board of Health, etc...