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Biointrusion of Protective Barriers at Hazardous Waste Sites

Center for Ecological Risk Assessment and Management, College of Natural Resources, Colorado State University, Ft. Collins, CO 80523.

^* Corresponding author (edr{at}picea.cnr.colostate.edu).

ABSTRACT

At locations throughout the world, hazardous wastes have been buried in an attempt to ensure the health and safety of the environment. The ability of simple and complex barriers to protect against biotic intrusion in the short- and long-term is questionable. Little research has been conducted to assess the risk that biota may pose to barrier integrity. Evidence of documented and potential cases of biointrusion of protective barriers by various species of plants, burrowing mammals, and invertebrates at various hazardous waste sites throughout the USA is examined to assess whether biointrusion has occurred. Studies documenting plant root intrusion were examined to assess their ability to affect barrier integrity. Various plant species, including kochia [Kochia scoparia (L.) Schrader], crested wheatgrass (Agropyron cristatum L.), big sagebrush (Artemisia tridentata ssp. wyomingensis Nutt.), and salt cedar (Tamarix ramosissima Ledeb.) were found to have penetrated into protective barriers in mesic and arid environments. There is also evidence of biointrusion by harvester ants (Pogonomymrmex owyheii) through rock barriers. Mice (Perognathus parvus, Peromyscus maniculatus), kangaroo rats (Dipodyms ordii), pocket gophers (Thomomys bottae), ground squirrels (Spermophilus elegans, S. townsendii), and prairie dogs (Cynomyous leucurus) are also a threat to the integrity of protective barriers. These results indicate that plants, invertebrates, and burrowing mammals pose a threat to barrier integrity and waste isolation. Engineered protective caps have been designed without the consideration of ecological principles and processes. The incorporation of these components into barrier designs may be crucial to their performance.