Weissmann Accurate modeling and prediction of contaminant transport and fate in groundwater systems requires that we produce detailed aquifer characterizations. Recently, the PI and colleagues developed a novel sequence stratigraphic approach to characterizing hydrofacies distributions for use in groundwater models on a stream-dominated alluvial fan system, thus integrating geological and hydrological assessment. Several questions resulted from this work that guides this proposed research project, including: 1) do sequences and systems tracts exist in other alluvial fan systems; 2) do sequences, bounded by clay-rich mature paleosols, compartmentalize groundwater flow into hydrostratigraphic units; and 3) can sequence stratigraphy provide a framework for improved groundwater modeling on other alluvial fan systems. Through sedimentologic, paleopedologic, and hydrogeologic analysis at the Lawrence Livermore National Laboratory (LLNL), a site with extensive core, geophysical well log, and 3D hydrologic test data, we intend to test hypotheses formed from these questions. Preliminary work at the LLNL site indicates that mature paleosols may bound hydrostratigraphic units, thus indicating that paleosol bounded sequences exist and that sequence geometry may strongly influence aquifer hydrodynamics. Through this work, we will (1) describe about 6000 meters of previously collected core, (2) assess paleosol morphology and chemistry, (3) model the stratigraphy, multi-scale facies distributions, groundwater flow, and contaminant transport within this complex aquifer system, and (4) assess data value to evaluate minimum data requirements for future work in similar geologic settings. These models will be tested against aquifer test and contaminant concentration data. A major objective of this work is to involve many student researchers in this project, thus several students will be directly involved in daily research activities. Additionally, aspects of this research will be incorporated into classroom activities, where students in an aquifer and petroleum reservoir assessment course will analyze core, construct the 3-D stratigraphic framework at a small site, and model the heterogeneity at the site. This will not only expose students to the research project, but will provide multiple 'realizations' of the stratigraphic character for uncertainty assessment of the modeling results.
