Rebuilding a septic drain field
Based on your rather telling but incomplete information, I have to caution you on your plans. This may have changed, I haven't had septic in 20-years. Not good &amp; not legal, if the field hasn't been unused for 20-years. This must be fully designed, tested, approved &amp; inspected to be proper, legal &amp; last 25 or more years.

If a newer field has to be re-used, all soil needs to be entirely removed &amp; replaced with a proper draining &amp; absorption mixture. A complete &amp; total deep excavation. The fork must be a fork &amp; not a single long pipe &amp; no fork tine can be any longer than 100' &amp; each must end with an inspection vent pipe. Each tine must be separated by dirt to avoid pooling &amp; enforce even distribution.