[en] This report presents the results of a series of evaluations to determine if the individual Category C tank systems retain sufficient structural integrity to continue being used for liquid storage. The approach used to reach the final certification/conclusion consisted of three phases, including: (1) Review of the original engineering design drawings and construction materials to determine whether the tank and line systems were capable of containing liquids without leaking (and also to check that the construction materials were compatible with liquids that might have been placed in these systems). While drawings in this report may be of poor quality, they are copies of the best available originals. (2) A qualitative corrosion assessment conducted in 1995 that further evaluated both the potential internal corrosion effects of materials in the tank and in the potential external corrosion effects of the backfill and native soil at the Oak Ridge National Laboratory (ORNL). The ability to accurately measure or predict the amount of corrosion present on both the internal and external walls of the tanks and pipelines is extremely limited. However, when available, data were used to assess the historical tank contents and usage and the probable corrosive effects on the tank system materials of construction. (3) Performance of monthly leak tests were completed on the tanks and annual leak tests were completed on associated testable pipelines. This task was judged to be the most important criteria for determining structural integrity due to the proven performance of the technology and processes involved