Preliminary assessment of geologic materials to minimize biological intrusion of low-level waste trench covers and plans for the future

The long-term integrity of low-level waste shallow land burial sites is dependent on the interaction of physical, chemical, and biological factors that modify the waste containment system. Past research on low-level waste shallow land burial methods has emphasized physical (i.e., water infiltration, soil erosion) and chemical (radionuclide leaching) processes that can cause radionuclide transport from a waste site. Preliminary results demonstrate that a sandy backfill material offers little resistance to root and animal intrusion through the cover profile. However, bentonite clay, cobble, and cobble-gravel combinations do reduce plant root and animal intrusion through cover profiles compared with sandy backfill soil. However, bentonite clay barrier systems appear to be degraded by plant roots through time. Desiccation of the clay barrier by invading plant roots may limit the usefulness of bentonite clay as a moisture and/or biological carrier unless due consideration is given to this interaction. Future experiments are described that further examine the effect of plant roots on clay barrier systems and that determine the effectiveness of proposed biological barriers on larger scales and under various stress conditions