THE EFFECTIVENESS OF BIOBARRIER LAYERS WITHIN PROTECTIVE CAPS ATPREVENTING PENETRATION OF WASTE SITES BY THE HARVESTER ANTPOGONOMYRMEX SALINUS OLSEN(HYMENOPTERA: FORMICIDAE)

摘要

This paper presents the current status of studies on the evaluation of the effectiveness ofrnproposed protective cap designs as biobarriers to harvester ant intrusion in near surfacernradioactive waste repositories in Idaho. This study evaluates a little considered biologicalrnproblem presented by ant colonies and their impact on the integrity of surface and near surfacernradioactive waste repositories. Ant colonies present a problem not only in reference to theirrnpotential breaching of protective caps, but also in their effect on soil hydrology. The impact ofrnant colonies on repositories may well represent not only a national problem but also anrninternational one. Currently, it would seem that a one meter deep biobarrier cap best meets therngoals for a protective cap over low level radioactive waste in shallow burial situations.rnThe harvester ant, Pogonomyrmex salinus, has been shown to excavate nests greater thanrn2-m deep in soils at the Idaho National Engineering and Environmental Laboratory (INEEL) inrnsoutheast Idaho. Harvester ants may excavate and remove buried waste from nuclear waste sitesrnas well as create conduits for waste and radionuclide migration. A biobarrier, which consists of arn30 cm layer of river cobble sandwiched between two 10 cm layers of chipped gravel, has beenrnshown in laboratory tests to create an impenetrable obstacle to ants, thereby disallowing theirrnexcavation beyond a desired depth.rnThe effectiveness of a 2.0-m deep protective cap with a gravel-cobble-gravel biobarrierrnlayer at preventing harvester ant intrusion was tested at the INEEL. Nests of harvester ants werernestablished on experimental biobarrier plots in 1996 and 1997. The nests were excavated inrn1999 to determine if ants had breached the biobarrier layer. In addition, soil moisture studiesrnwere conducted in order to learn how water movement through soil is affected by the presence ofrnant nests.