Standardization of Borehole Data to Support Vadose Zone Flow and Transport Modeling

The vadose zone beneath the USDOE’s Hanford Site in southeastern Washington State (Fig. 1) received approximately 1 trillion liters (450 billion gallons) of liquid waste, some contaminated with radioactive and hazardous contaminants. Today, Hanford is engaged in the world’s largest environmentalcleanup project, and a variety of conceptual and mathematical vadose zone models have been developed to support individual cleanup objectives. Traditional approaches to modeling the stratigraphic framework at Hanford have used simple homogeneous and horizontally stratifi ed hydrogeologic units. However, as computer-processing capabilities have advanced, more emphasis has been placed on improving spatial resolution and quantifying uncertainty in representing the geologic framework and its key model parameters. Newer approaches are focusing on geostatistical simulation of the sequence-stratigraphic relations of lithofacies and on the geostatistical distributions of fl ow-and-transport properties within those facies. These newer approaches require more rigorous quantitative treatment of geologic data than are normally supported by the mostly qualitative nature of borehole geologic information. Thus, efforts are being made to standardize borehole geologic data so they can be used in a systematic and quantitative way to defi ne the spatial distribution of fl ow-andtransport properties in support of vadose zone modeling. Borehole geologic data provide the foundation for interpreting the subsurface framework and spatial distribution of the fl ow-and-transport properties. Surface geophysical data can be useful for extrapolating between boreholes; however, they too depend on borehole geologic data for calibration and validation of the geophysical responses. Borehole data are composed of various types and quality of data, from qualitative fi eld observations (driller’s logs) to quantitative laboratory analyses of borehole samples (e.g., grain-size distributions) and borehole geophysical logs. Many of these data are collected in nonstandardized formats that are diffi cult to incorporate into numerical simulation. Efforts are being made at the Hanford Site to standardize, manage, and analyze borehole geologic data to produce both regional sequence-stratigraphic hydrogeologic models and sitespecifi c geostatistical representations of spatial distributions of lithofacies and their hydrogeologic and geochemical properties. Although the regional stratigraphic units for the Hanford Site are well documented, the differentiation of smaller-scale depositional elements and inherent fl ow-and-transport properties has been limited and diffi cult to quantify. Collecting new subsurface data is time consuming and expensive. Thus, it is important to extract as much information as possible from existing borehole Standardization of Borehole Data to Support Vadose Zone Flow and Transport Modeling