An Integrated System for Vadose Zone Monitoring, Model Calibration, Performance Assessment, and Prediction (MCAP) in Hanford's T Tank Farm

The Hanford Site has 149 underground single-shell tanks that store hazardous radioactive waste. Many of these tanks and their associated infrastructure (e.g., pipelines, diversion boxes) have leaked. Some of the leaked waste is projected to have entered the groundwater. The largest known leak occurred from the T-106 Tank in 1973. Most of the contaminants from that leak still reside within the vadose zone beneath the T Tank Farm. To minimize movement of this residual contaminant plume, an interim infiltration barrier will be constructed on the ground surface. This barrier is expected to prevent infiltrating water from reaching the plume and moving it further towards groundwater. An integrated system will be used for vadose zone moisture monitoring, model calibration, performance assessment, and prediction (MCAP). The system is to be broadly- designed so that the data can be used for multiple purposes. In addition to monitoring soil water movement both under the proposed barrier and adjacent to it, the collected data can also be used to characterize vadose zone hydraulic properties and to calibrate a numerical model. The calibrated model can then be used to assess the performance of the infiltration barrier and to predict water flow and contaminant transport under conditions with and/or without a barrier. A MCAP system is being applied to the Hanford's T Tank Farm. Soil water content is to be monitored using both neutron and capacitance probes; soil water pressure and soil temperature will be monitored with heat dissipation sensors; and water flux will be measured using water fluxmeters. These instruments will be installed in direct push probe holes advanced by a hydraulic hammer unit. Excluding neutron probe measurements, all data collection and data transmittal will be sent to an automated central server. This design allows measurements to be taken continually and reduces the need for personnel to enter the farm thereby increasing worker safety. It is expected that the integrated MCAP system will produce a valuable analysis and be cost effective.