Ill. Admin. Code tit. 35 § 848.407
An owner or operator may satisfy the requirements of this Subpart by establishing more than one financial mechanism listed in Section 848.406 per site. These mechanisms listed in Section 948.406 include trust funds, surety bonds guaranteeing payment, and letters of credit. The mechanisms must be as specified in Sections 848.410, 848.411, and 848.413, respectively, except that it is the combination of mechanisms, rather than any single mechanism, that must provide financial assurance for an amount at least equal to the current approved removal cost estimate. An owner or operator that uses a trust fund in combination with a surety bond or a letter of credit may use the trust fund as the standby trust fund for the other mechanisms. A single standby trust fund may be established for two or more mechanisms. The owner or operator may use any or all of the mechanisms specified in Sections 848.410, 848.411, and 848.413 to provide for removal.
Ill. Admin. Code tit. 35, § 848.407