Analysis of vadose zone tritium transport from an underground storage tank release using numerical modeling and geostatistics

Numerical and geostatistical analyses show that the artificial smoothing effect of kriging removes high-permeability flow paths from hydrogeologic data sets, reducing simulated contaminant transport rates in heterogeneous vadose zone systems. Therefore, kriging alone is not recommended for estimating the spatial distribution of soil hydraulic properties for contaminant transport analysis at vadose zone sites. Vadose zone transport is modeled more effectively by combining kriging with stochastic simulation to better represent the high degree of spatial variability usually found in the hydraulic properties of field soils. However, kriging is a viable technique for estimating the initial mass distribution of contaminants in the subsurface.; One of the more challenging problems faced by earth scientists in vadose zone studies is the characterization of heterogeneous field sites with limited data. This dissertation presents and demonstrates a methodology that will increase substantially the effectiveness of vadose zone contaminant transport analyses while reducing the high cost usually associated with site characterization in heterogeneous soils. Our approach combines stochastic simulation and ordinary kriging with soil property correlation and numerical modeling to optimize the utilization of scarce data.; The study site is the Building 292 Area at Lawrence Livermore National Laboratory, where the soil close to an underground tank storing tritiated water was contaminated with {dollar}rmsp3H{dollar} at levels up to 220 million pCi/L of soil water. Our principal objectives were to investigate the applicability of geostatistical techniques, soil property correlation, and numerical modeling to study the transport behavior of tritium at the heterogeneous vadose zone site, and to use data available from site characterization and monitoring to predict the impact of the release on future soil and groundwater quality at the site.; The analysis shows no serious long term threat to groundwater quality at the site, but high soil water {dollar}rmsp3H{dollar} concentrations will persist in the vadose zone for several decades. The impact of the release on groundwater quality is substantially reduced by a blacktop that partially covers the site. Vapor diffusion is not important to {dollar}rmsp3H{dollar} transport under current site conditions.