In areas where on‑site sewage disposal systems will be installed, the size and relative location shall be governed by the Illinois Department of Public Health and Union County Sewage Code regulations in effect at the time. In addition, the following requirements shall also apply:
(A) On each lot, there shall be an area preserved for the construction of an additional drain field system should the original drain field fail. The area set aside for a second drain field shall be of a size and so located that a drain field can be constructed that will meet all standards on size and setbacks recommended by the Illinois Department of Public Health and the County Health Department or their successor.