O.C.G.A. § 32-2-73: Supplemental and extension agreements.

The department shall be authorized to execute supplemental agreements to the original contract covering changes or revised or new unit prices and items and supplementing the original contract not to exceed a 20 percent increase in cost of the project and to execute extension agreements affecting the length of the project which may be increased by adding sections to said project or by relocation of said project not to exceed 20 percent of the total length of the project or 20 percent of total contract cost.