Engineered Barrier Testing at the INEEL Engineered Barriers Test Facility: FY-1997 and FY-1999

摘要

Engineered barriers of two designs are being tested at the Engineered Barriers Test Facility (EBTF) at the Idaho National Engineering and Environmental Laboratory. This report describes the test facility, barrier designs, and instruments used to monitor the test plots. Wetting tests conducted on the test plots in FY-97 are described and data collected from monitoring the test plots before, during and after the wetting tests are used to evaluate the performance of the covers during FY-97 and FY-98. Replicates of two engineered barrier designs were constructed in the EBTF cells. The first design comprises a thick, vegetated soil cover. The second design incorporates a capillary/biobarrier within the vegtated soil cover. The capillary barrier uses the textural break between an upper, fine textured soil and a lower, coarser-textured gravel layer to inhibit drainage under unsaturated conditions while increasing soil moisture storage in the root zone. Evaporation and transpiration by plants (although the test plots have not yet been vegetated) are used to recycle water stored in the soil back to the atmosphere. A geotextile fabric is used to maintain separation of the soil and gravel layers. A thick layer of cobbles beneath the gravel layer serves as a biobarrier to prevent intrusion of plant roots and burrowing animals into underlying waste (there is no waste in the test plots). Each test plot was instrumented with time domain reflectometry probes and neutron probe access tubes to measure moisture contents, tensiometers, heat dissipation sensors, and thermocouple psychrometers to measure matric potentials, thermocouples to measure soil temperature, and ion-exchange resin beads to monitor tracer movement. Each drainage sump is equipped with a tipping bucket instrument and pressure transducer to measure drainage. Precipitation is measured using a heated rain gauge located at the EBTF. Instrument calibration equation coefficients are presented, and data reduction techniques are described. The wetting tests were designed to stress the test plots to the maximum by forcing drainage to occur. Drainage generally occurred two to three days following the start of the wetting test. Drainage from the capillary/biobarrier test plots stopped sooner than drainage from the thick soil test plots. Similar results were observed in drainage data collected in FY-98 following the spring thaw. Drainage from the capillary/biobarrier test plots following the winter of 1998 represents about one-third of the precipitation occurring during that period compared to two- thirds of the precipitation from the thick soil test plots. By limiting drainage, the capillary/biobarriers increased water storage in the upper portions of the test plots compared to the thick soil barriers. The data evaluated in this report come from an ongoing project. The aftereffects of the wetting tests continue to be monitored. Long-term monitoring under ambient conditions, the application of additional treatments to the test plots, and numerical modeling are planned for the future.