My house and septic system are 7 years old. I have had water standing at the lower half of the last leach line for some time. First only after a heavy rain, now all the time. This line is the last of five lines at the end of the leach field. Can I install a diverter valve to give this line a rest or is there another fix short of a new field. This line is also in the lowest part of the leach field. Any help would be appreciated

I would leave it alone and check back once a year. If you were able to close this line off you will find one of the other 4 lines is now the low line. It is also ill advised to attempt to get a system designed with 5 lines to work with 4. I am assuming your home passed a perc test befire the lines were installed, right?