An enhanced selective oxidative alkaline leaching (ESOAL) process has been developed for the removal of chromium from high level waste (HLW) tank sludges. Because of the adverse effect of excess chromium on the vitrification process, chromium removal becomes a critical factor in the pretreatment of underground storage tanks (USTs) containing nuclear waste. The ESOAL process described here uses a unique approach based on the innovative combination of an effective oxidant and sonochemical oxidation, achieving efficiencies and removal rates substantially better than either of the processes used independently. Results are shown here for the ESOAL treatment of a tank sludge simulant (Hanford tank S-101). The effects of different variables (e.g., time, ultrasound power, temperature, sodium hydroxide concentration, and the use of an oxidant) on the amount of sludge dissolved are presented.