SUMMARY

Engineered-cover studies at our site will provide valuable information on the performance of GCL/asphalt- and capillary-barrier designs in an arid setting. These vegetated covers can also be considered ET covers and the upper parts are similar to monolithic covers. A variety of instruments, including neutron probes, time-domain reflectometry probes, heat-dissipation sensors, and thermocouple psychrometers provide a comprehensive understanding of water movement in these engineered systems. Water-balance data are used to assess the performance of the covers. The results of this study will also allow us to compare different types of instrumentation and examine the robustness and longevity of various instruments, as well as predict how the engineered barriers will perform over actual disposal units. Preliminary results suggest that:

  • Both covers were initially wetter than the natural system owing to the addition of water to achieve optimal compaction and because of precipitation during construction.
  • Most instrumentation systems are performing well. The use of TDR to monitor water content is limited because of signal attenuation as a result of high conductivities.
  • The application of EM induction as a noninvasive method for monitoring water content at this site is complicated by the spatial and temporal variability in electrical conductivity as indicated by the TDR conductivity monitoring.
  • Monitoring of subsurface water contents, matric potentials, and electrical conductivity in response to irrigation indicates that the water moves through these systems predominantly by piston-type flow.
  • To date, there has been no significant movement of water through either the GCL/asphalt barrier or the capillary barrier.

 

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Environmental Quality