When water is encountered during directional drilling, the most common method to try and stop it is pumping concrete. However, if there is a large volume of water, the concrete simply washes away and doesn’t seal the leak. Concrete also shrinks as it dries, so new leak paths are formed. In this instance concrete was tried and did not work, so polyurethane grout was injected 150 feet into the problem area. The grout used to stop the water flow was Hyperflex, a moisture activated hydrophobic polyurethane that is NSF/ANSI/CAN 61 approved for contact with potable water. Hyperflex is manufactured by SealGuard, Inc. and grouting was performed by Sub-Technical, Inc.