Two-Decade Instrument Performance for Hydrological Monitoring at the Prototype Hanford Barrier.

Surface barriers have been proposed for use at the Department of Energy’s Hanford Site as a means to isolate certain radioactive waste that may not be exhumed. The Prototype Hanford Barrier was constructed in 1994 and is expected to perform for 1000 years by limiting water, plant, animal, and human intrusion and minimizing erosion. Extensive instrumentation is used to monitor the hydrological regime above, within, below, and around the barrier. Specifically, natural precipitation and irrigation are measured with rain gauges, runoff water with a runoff flume, soil water content within the barrier at 12 stations with a neutron probe, a capacitance probe, and time-domain-reflectometry probes, and soil water pressure with heat-dissipation-units and gypsum blocks. Drainage through the barrier and the side slopes is measured with 12 water collection vaults, respectively, for 12 zones. Each drainage vault is equipped with a dosing siphon, a pressure transducer, and a tipping bucket to measure the volume of drainage. The percolation through the asphalt layer was monitored using a lysimeter. During the near two-decade monitoring period, some of the instruments stopped functioning, while others still function normally till present. This presentation will summarize the performance of these instruments.