[en] The South Tank Farm (STF) is a series of six, 170,000-gal underground, domed storage tanks that were placed into service in 1943. The tanks were constructed of a concrete mixture known as gunite. They were used as a portion of the Liquid LOW-LEVEL WASTE (LLLW) System for the collection, neutralization, storage, and transfer of the aqueous portion of the radioactive and/or hazardous chemical wastes produced as part of normal facility operations at Oak Ridge National Laboratory (ORNL). Although the last of the tanks was taken out of service in 1986, they have been shown by structural analysis to continue to be structurally sound. An attempt was made in 1983 to empty the tanks; however, removal of all the sludge from the tanks was not possible with the equipment and schedule available. Since removal of the liquid waste in 1983, liquid continues to accumulate within the tanks. The in-leakage is believed to be the result of groundwater dripping into the tanks around penetrations in the domes. The tanks are currently being maintained under a Surveillance and Maintenance Program, which includes activities such as level monitoring, vegetation control, High Efficiency Particulate Air filter leakage requirement testing/replacement, sign erection/repair, pump-out of excessive liquids, and instrument calibration/maintenance