The Kentucky Lock, Dam and Powerhouse Project is located 22.4 miles up the Tennessee River from Paducah, KY. The Kentucky Lock Addition Project includes the addition of a 110-foot x 1200-foot lock landward of the existing 110 foot x 600 foot lock. The Mississippian aged limestone has been severely dissolved resulting in challenging foundation conditions under the upstream cellular sheet pile cofferdam that required using a variety of construction techniques and some quick adjustments to the design. There is a dramatic escarpment in the rock surface upstream of the Kentucky Lock addition that drops over 100 feet. This paleokarst feature is buried by residual soils and unconsolidated sediments. Pre-construction exploration for the upstream cofferdam, which had to be conducted from floating plant, also encountered this structure and indicated a complex network of clay filled cavities in the rock adjacent to it. The Upstream Cofferdam was located at the brink of the escarpment. Information from the exploration indicated that a conventional grout curtain could be successfully installed under the cofferdam. Sliding stability would require the installation of 10-foot diameter reinforced concrete caissons that were to be tied into a concrete cap in the base of the cofferdam. The Judy Corporation performed the grouting using balanced/stabilized grout and an automated information system. During this operation several very large karst features were encountered that compromised the continuity of the seepage cutoff. The District elected to use overlapping jet grout columns to provide a continuous barrier through the worst of these. In addition, the irregularity of the top of rock lead to a reevaluation of the sliding stability design and used the irregularity of the rock surface as a shear key. This eliminated the need for several of the caissons.