T Farm Interim Surface Barrier Vadose Zone Monitoring FY08 Fourth-Quarter Status Report

This report briefly summarizes the system status and monitoring results of Nests A, B, C and D and the Meteorological Station in the T Tank Farm from July to September, 2008. All the sensors except the two drain gauges were functional. The layout of the instrument Nests and a detailed analysis of the FY07 data were summarized in the FY07 annual report (PNNL-17306, Zhang et al. 2008). Nests C and D reside under the surface barrier, Nest B near the edge of the barrier, and Nest A outside the barrier. For detailed description of the design of the monitoring system, please refer to the 'T Tank Farm Interim Surface Barrier Demonstration - Vadose Zone Monitoring Plan' (PNNL-16538, Zhang et al. 2007). The primary variables monitored include: soil-water content measurements by the capacitance probes (CPs), normalized neutron counts (as a reflection of soil water content) by a neutron probe (NP) soil-water pressure measurements by the heat dissipation units (HDUs), and soil-water flux measurements by the drain gauges. The secondary variables monitored include: soil temperature measured by HDUs, air temperature and precipitation from the T Farm Meteorological Station, temperature within the datalogger enclosures, and battery voltages. To check the system's functionality, measured air temperature, temperature within the datalogger enclosures, and precipitation were compared with those from the Hanford Meteorological Station (HMS).