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.