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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology APPENDIX E DISSENTING STATEMENT ON ISSUE 1 June Ann Oberdorfer February 28, 1995 Of the seven issues raised by the Wilshire group, the first about transfer of contaminants to the water table is the most critical one from a human health and water resource perspective. The thick vadose [unsaturated] zone and dry climate are the first line of defense. Since the repository is designed as a passive system (no liners, no leachate collection, no monitoring or maintenance after the first 105 years after closure), it is imperative that our understanding of the rates of water movement through the vadose zone does not have large uncertainties. We need to have a reasonable assurance that any radionuclides which escape from the waste will not be able to migrate to the water table on time frames of concern. The bulk of the reliable soil physics data and the chloride data point to minimal downward migration of soil water at the Ward Valley site. There are two sets of data, however, which prevent there being a reasonable assurance that there is minimal water flux at the site. The first of these is the detection of tritium in soil vapor samples at 30 m depth. If indeed there is tritium at that depth, then downward migration of soil water occurs at a much faster rate than any acknowledged in the license application and at a rate that would indicate the possibility of rapid transport of contaminants to the ground water. The second data set indicates the apparent presence of a downward vertical hydraulic gradient in the ground water beneath the site. One reasonable explanation for this is that local ground-water recharge is occurring, with the flow occurring downwards away from this region to remove the added fluid mass. United States Ecology, its consultants, and the Department of Health Services have treated both data sets as accurate without providing credible explanations for their occurrence. They have not questioned the validity of the data. The committee, on the other hand, has raised questions about the methods used in collecting these data. The validity of the data is unresolved and not resolvable without additional field work. Since the data sets indicate much more rapid and more copious vadose zone water transport than acknowledged in the license application, they raise considerable concern about the suitability of the site for a LLRW repository. Without a resolution of this uncertainty by showing the absence of tritium at depth and the absence of a downward vertical gradient (or a defensible explanation for both phenomena), there cannot be reasonable assurance that water and contaminants will not be rapidly transmitted to the water table. The report states that ''site characterization data must be of sufficient quantity and quality to address the areal variability of percolation at a potential site...'' The quantity and
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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology quality do not exist for Ward Valley to provide reasonable assurance that the site is suitable for long-term storage of radioactive wastes. Sampling of soil cores and analysis of soil moisture for tritium is not a difficult or lengthy task. Determination of the deviation from verticality of the wells is not one either. Satisfactory finding from these two tasks are important to dispel uncertainties about this site. In addition, we need to be cautious about extrapolating from the field data to the engineered facility. The field data represent conditions and conclusions for the undisturbed site. Digging a large trench in the ground, filling it with containerized waste, and capping it with a raised cap greatly alter the natural system. There are many ways in which construction of the repository can modify infiltration and evapotranspiration. Subsidence of the waste can cause depressions in the cap surface where water could pond, particularly during times of heavy rainfall, and infiltration would then be greatly enhanced. Also during heavy rainfall periods, the troughs between the trenches will concentrate surface runoff into a small area (instead of its being spread over a very large area as in the natural system) where infiltration will be enhanced. Since the raised cap will have no surface water runon from upslope areas, much of the time the soil moisture will be reduced and hence the cap will not be able to support as dense a vegetative cover. During infrequent periods of heavy rainfall, more water may infiltrate than can be evapotranspired by the sparse vegetation before the water has time to percolate deep into the cap and then into the waste. Studies referenced in the report have found that unvegetated add regions can have significant water fluxes and water fluxes could also be greater through a sparsely vegetated cap during periods of heavy rainfall. Only to the extent that the engineered facility mimics the natural system (no ponding, no concentrated channelization, sufficiently dense vegetative cover), can we argue that transfer of contaminants to the water table is unlikely.
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