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Past Research

The Protective Cap/Biobarrier Experiment A study of Alternative Evapotranspiration Caps for the Idaho National Engineering and Environmental Laboratory

Shallow land burial is the most common method for disposing of industrial, municipal, and low-level radioactive waste, but in recent decades it has become apparent that conventional landfi ll practices are often inadequate to prevent movement of hazardous materials into ground water or biota. Most waste repository problems result from hydrologic processes. When wastes are not adequately isolated, water received as precipitation can move through the landfill cover and into the wastes. Presences of water may cause plant roots to grow into the waste zone and transport toxic materials to aboveground foliage. Likewise, percolation of water through the waste zone may transport contaminants into ground water.

In semiarid regions, where potential evapotranspiration greatly exceeds precipitation, it is theoretically possible to preclude water from reaching interred wastes by:

  1. Providing a sufficient cap of soil to store precipitation that falls while plants are dormant and
  2. establishing sufficient plant cover to deplete soil moisture during the growing season, thereby emptying the reservoir of stored water.

The Protective Cap/Biobarrier Experiment (PCBE) was established in 1993 at the Experimental Field Station, INL Site, to test the efficacy of four protective landfill cap designs. The ultimate goal of the PCBE is to design a low maintenance, cost effective cap that uses local and readily available materials and natural ecosystem processes to isolate interred wastes from water received as precipitation. Four evapotranspiration (ET) cap designs, planted in two vegetation types, under three precipitation regimes have been monitored for soil moisture dynamics, changes in vegetative cover, and plant rooting depth in this replicated field experiment.


From the time it was constructed, the PCBE has had four primary objectives which include;

  1. Comparing the hydrologic performance of four ET cap designs,
  2. Examining the effects of biobarriers on water movement throughout the soil profile of ET caps
  3. Assessing the performance of alternative ET cap designs under current and future climatic scenarios, and
  4. Evaluating the performance of ET caps planted with a diverse mix of native species to those planted with a monoculture of crested wheatgrass.

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