Ill. Admin. Code tit. 35, § 813.304 – Updated Groundwater Impact Assessment

a) The applicant shall conduct a new groundwater impact assessment in accordance with 35 Ill. Adm. Code 811.317 if any of the following changes in the facility or its operation will result in an increase in the probability of exceeding a groundwater standard beyond the zone of attenuation:
1. 1) New or changed operating conditions;
2. 2) Changes in the design and operation of the liner and leachate collection system;
3. 3) Changes due to more accurate geological data;
4. 4) Changes due to modified groundwater conditions due to offsite activity;
5. 5) Changes due to leachate characteristics.
b) If the operator certifies that the conditions applicable to the original assessment have not changed in such a way as to result in violation of groundwater standards pursuant to 35 Ill. Adm. Code 811.320, outside the zone of attenuation and no monitoring well shows concentrations of constituents in groundwater greater than such groundwater standards, then a new groundwater impact assessment need not be performed.