Groundwater was leaking through the joints of these underground chambers at a wastewater treatment plant. Injecting polyurethane grout from inside the structure would provide an ideal fix to stop the groundwater from infiltrating. However, these chambers have various pipes and support structures that would make entry and performing the work nearly impossible. The solution was to still inject polyurethane grout, but from the outside. This method, often called soil grouting or curtain grouting, utilizes metal pipes driven down the outside of the structure to the problem areas. The pipes contain several holes that the grout can be expelled from when pumped. Groundwater will then carry the grout throughout the leak path, then react into a foam, thus stopping the inflow. The grout used was Hyperflex, manufactured by SealGuard, Inc. Hyperflex is a moisture activated, hydrophobic material that is NSF/ANSI/CAN 61 approved for contact with potable water. The grouting was performed by Sub-Technical, Inc.