Tank anchorage requirements have evolved with various updates in AWWA D100. Many older tanks have inadequate foundations, which has been a cause of numerous tank failures. The rocking of a tank in a seismic event causes the bottom shell to bulge just above the connection where the shell meets the floor. There are several options to improve the foundation of an existing tank without having to build a new tank. They include adding a new foundation under the tank shell, doweling into an existing concrete foundation and adding anchor bolts, and adding a weldment to the tank that is connected to drilled soil/rock anchors.