US lawIllinoisRegulationsTitle 35 — ENVIRONMENTAL PROTECTIONCHAPTER I: POLLUTION CONTROL BOARDSUBCHAPTER a: PERMITS AND GENERAL PROVISIONSPart 204 — PREVENTION OF SIGNIFICANT DETERIORATIONSubpart B204.44035 Ill. Adm. Code 204.440High TerrainYear: 2026Length: 25 wordsOfficial source Section 204.440 High Terrain "High terrain" means any area having an elevation 900 feet or more above the base of the stack of a source.Previous35 Ill. Adm. Code 204.430Next35 Ill. Adm. Code 204.450