1. a) The volume of regulated substances or pesticides for which each person is responsible;
2. b) Consistent with the provisions of 35 Ill. Adm. Code 742 and the remediation of the site in a manner consistent with its current and reasonably foreseeable future use, the degree of risk or hazard posed by the regulated substances or pesticides contributed by each person;
3. c) The degree of each person's involvement in any activity that proximately caused or contributed to the release or substantial threat of a release of regulated substances or pesticides; and
4. d) Any other factors relevant to a person's proportionate share.

In determining proportionate shares under this Part, the Board will consider any or all factors related to the degree to which the performance or costs of a response result from a person's proximate causation of or contribution to the release or substantial threat of a release. These factors include the following: