US lawIllinoisRegulationsTitle 35 — ENVIRONMENTAL PROTECTIONCHAPTER I: POLLUTION CONTROL BOARDSUBCHAPTER d: UNDERGROUND INJECTION CONTROL AND UNDERGROUND STORAGE TANK PROGRAMSPart 731 — UNDERGROUND STORAGE TANKSSubpart B731.12135 Ill. Adm. Code 731.121Upgrading of Existing Systems (Repealed)Last amended: 1992Year: 2026Length: 9 wordsOfficial source Section 731 Section 731.121 Upgrading of Existing Systems (Repealed)Previous35 Ill. Adm. Code 731.120Next35 Ill. Adm. Code 731.122