Ill. Admin. Code tit. 17, § 3702.90 - Datum For Dam Elevations
All elevations for Class I and Class II dams shall be on the National Geodetic Vertical Datum (same as mean sea level (MSL) 1179 adj.). Where possible, Class III dams shall also be on the NGVD datum. (Datum means the level surface used for reference in determining the elevations of features of a dam)
Notes
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