Evaluation and monitoring plan for consolidation tanks: Gunite and Associated Tanks Operable Unit, Waste Area Grouping 1, Oak Ridge National Laboratory, Oak Ridge, Tennessee

This report describes the results of an integrity evaluation of Tanks W-8 and W-9, part of the Gunite and Associated Tanks (GAAT), in the South Tank Farm at Oak Ridge National Laboratory (ORNL), together with a plan for monitoring those tanks for potential releases during the GAAT CERCLA treatability study and waste removal activities. This work was done in support of an ORNL plan to use W-8 and W-9 as consolidation tanks during remediation of the other tanks in the North and South Tank Farms. The analysis portion of the report draws upon both tank-internal measurements of liquid volume change and tank-external measurements of the change in electrical conductivity of the groundwater in the dry wells adjacent to each tank. The results of the analysis show that both W-8 and W-9 are liquid-tight and are suitable for use as consolidation tanks. The recommended monitoring plan will utilize the dry well conductivity monitoring method as the primary release detection tool during the CERCLA activities. This method is expected to be able to detect releases of less than 0.5 gal/h with a 95% probability of detection, most of the time. The results described here validate three prior independent efforts: a liquid integrity assessment made in 1995, a structural integrity assessment made in 1995 by experts in the field of gunite tanks, and a structural integrity assessment made in 1994 using a three-dimensional, finite-element computer model. This work, along with the three prior efforts, shows that Tanks W-8 and W-9 are structurally sound and liquid-tight. Based upon this work it is concluded that these tanks are suitable for use as consolidation tanks during the GAAT CERCLA treatability study and waste removal actions and it is recommended that the tanks be monitored for potential releases during this period using the methods described in this report