Grout curtains have been widely used in the United States in order to mitigate or control seepage under and around a civil works structures throughout the 20th Century. Using a variety of methods, the purpose of a grout curtain is to provide a reduction in the seepage across the installation. Reduction in seepage can be particularly important in karst geology where the presence of solution widened openings in the rock that occur along bedding, joints and other features in the rock can sometimes be quite large. These features may be partially or completely infilled with clay and other materials. Grouting operations may not fully remove infilled materials and can leave weak points in the curtain that are exploited by the groundwater flow over time. Even with a well-developed ground investigation, it is impossible to completely define all the water pathways in the karst rock. Fortunately, modern computer codes supply a means to model the effectiveness of a grout curtain and to explore the consequences of a breach of that curtain in the subsurface. For this study, a lock excavation problem was set up in RS2 using the geological context from a lock excavation project that reflects the karst issues that have been encountered in multiple lock and dam projects in Tennessee and Kentucky. Two known potential breach points were established, and the effects were modeled. The results led to insights into the size of features that could cause constructability issues. In addition, the results are used to target specific zone of interest with an instrumentation and monitoring program.