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Vadose Zone Model at Pantex

In FY 1996, PNNL provided technical assistance to Battelle Columbus Operations (BCO) in their ongoing assessment of contaminant migration at the Pantex Plant in Amarillo, Texas. Two activities were involved: developing a strategy for modeling the vadose zone and predicting deep drainage rates. This information was later used by BCO to predict contaminant loading to the underlying unconfined aquifer and to support analyses of remedial activities involving surface alterations or the subsurface injection/withdrawal of liquids or gases.

The first activity had two objectives: 1) describe the current understanding of the vadose zone at the Pantex Plant, and 2) determine the adequacy of existing data from previous work to support the development of vadose zone models. This activity involved reviews of prior studies, modeling activities and available data such as geologic cross-sections and sediment properties, primarily particle size distributions or descriptions. The results were incorporated into internal BCO documents.

The second activity concerned the estimation of deep drainage rates for the major surface features at the Pantex Plant including ditches and playas, natural grassland, dryland crop rotation, unvegetated soil and graveled surfaces (Fayer et al. 1995). All estimates were derived using existing data or best estimates; no new data were collected. The modeling framework used to estimate the rates was described to enable future correlations, improvements and enhancements.


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