"Tolerance zone" means the approximate location of underground utility facilities or CATS facilities defined as a strip of land at least 3 feet wide, but not wider than the width of the underground facility or CATS facility plus 1-1/2 feet on either side of such facility based upon the markings made by the owner or operator of the facility. Excavation within the tolerance zone requires extra care and precaution including, but not limited to, as set forth in Section 4.
220 ILCS 50/2.7