High pressure water infiltration was impeding completion of this CSO tunnel. To control the water, polyurethane grout was injected into the problem areas. There were two types of polyurethane grout used on this project, SealGuard II and Hyperflex. SealGuard II is a fast-reacting dual component grout that was used to control the heavy water inflow. Any remaining leaks were then grouted with Hyperflex. Hyperflex is much slower reacting than SealGuard II, which enables better migration into smaller voids. Hyperflex is a single component hydrophobic polyurethane that is moisture activated and is NSF/ANSI/CAN 61 approved for contact with potable water. SealGuard II and Hyperflex are manufactured by SealGuard, Inc. The grouting was performed by Sub-Technical, Inc.