The transition of gibbsite to boehmite is of interest with regard to high level waste processing associated with the Hanford and Savannah River sites. Both materials have been observed in core samples. From the temperature histories of the waste, it is possible that some fraction of gibbsite has been converted to boehmite. This paper describes thermal gravimetric analysis studies of products resulting from controlled temperature measurements of pure gibbsite in NaOH. Results indicate that the gibbsite to boehmite transformation can take place at temperatures as low as 100 degrees C. This information, along with available data on waste inventories and temperature histories, may be used to estimate the fractions of gibbsite and of boehmite in a given waste tank. Site engineers can then tailor the sludge leaching process for a particular tank to account for the delayed dissolution of boehmite, allowing separation of the aluminum and processing as a low activity waste.