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.