Research Summaries Fluid-Chemical Transport Investigations Building on their previous findings that film flow is an important mechanism for fast fluid transport along fractures in the unsaturated zone, researchers can now demonstrate that even in rocks with low matrix permeability (<10-15 m2) but containing fracture apertures larger than 50 microns, fast paths for fluid flow will occur in the vadose zone, and these films will transport colloids. This work verifies that contaminants sorbed onto colloids smaller than the film thickness may be transported effectively from the vadose zone to the ground water. Efforts continue to accurately model subsurface multiphase fluid and heat flow, along with solute transport and chemical reactions. By incorporating reactive chemistry into the framework of the exiting TOUGH2 code, ESD researchers have been able to model ore-forming processes such as supergene copper enrichment and to predict the thermal, hydrological and chemical processes that are likely to occur around a thermal source that simulates conditions in a high-level nuclear waste repository. Molecular modeling of cesium cation (137Cs+) - smectite clay interlayer systems has confirmed the previous findings from bulk diffusion experiments that clay liners will impede the mobility of radioactive 137Cs+, a fact important to the design of nuclear waste containment facilities. Prior to this study, detailed experimental characterization of this system proved difficult due to the high degree of disorder within these clays. Isotope Geochemistry The Center for Isotope Geochemistry (CIG) is a state-of-the-art analytical facility established in 1988 for the measurement of concentrations and isotopic compositions of elements in rocks, minerals and fluids in the earth's crust, atmosphere and oceans. Fundamental research conducted at this center is directed at finding new ways to use isotopic information to study earth processes such as long-term climate changes and the way mantle-derived or deep crustal fluids move through the crust. In a effort to reconstruct global climate and climate changes during the past 20,000 years, CIG researchers measured the oxygen and hydrogen isotope ratios (d18O and dD) in Antarctic ice cores from three locations to develop a model that relates isotopic compositions to water available in the ancient atmosphere and past surface temperatures. They have found clear evidence in the ice cores for the temperature transition from the last glacial maximum to the warmer and wetter Holocene, and found evidence that temperatures during the last glacial maximum were substantially lower than previously estimated on the basis of d18O data and the modern spatial relationships. The presence of He, C, and O isotopes in approximately 250 samples of fault gouge, breccia and host rocks collected along the San Andreas and adjacent faults confirms that a significant fraction of He is of mantle origin and is accompanied by deep crustal water and CO2. These findings support earlier results suggesting that deep crustal and mantle fluids enter and lubricate the fault zone, thus causing the low-friction conditions observed from seismological and deformation data. In their continuing study of a present-day volcanic system, researchers have found that co-variations between He and Nd isotopes in olivines from continental basalts can be used to differentiate between separate magma chambers and to assess the rates for heat and magma recharge into the crust. Advanced Computation for Earth Imaging The Center for Computational Seismology (CCS) serves as the LBNL and UC Berkeley nucleus for seismic research related to data processing, advanced imaging and visualization. In recent years, a great deal of cross-fertilization between seismologists and other geophysicists and hydrogeologists has developed within the division, resulting in collaborations on a wide variety of fundamental imaging problems, some of which are reported here. Researchers have successfully demonstrated the use of joint geophysical-hydrological data sets for estimating stochastic hydrologic parameters of a test site. Using data collected at the Oyster, Va., bacterial transport test site, they have been able to integrate hydraulic conductivity information from flowmeters and radar cross-hole tomograms to obtain improved images of permeability. Researchers have completed a major study of wave propagation along the San Andreas fault zone as part of the Parkfield Prediction Program. On the basis of more than 6,000 natural earthquakes and 720 source-receiver paths obtained from a controlled-source program, they have developed a detailed elastic model confirming that there are temporal velocity changes occurring in a region suspected to be the nucleation area for past and future magnitude-6 earthquakes. These velocity variations are strongly believed to be related to changing fluid conditions in the shallow section of the fault zone. Researchers have also developed and tested advanced techniques for modeling elastic and electromagnetic wave propagation through media heterogeneous in two and three dimensions. In one study they treated elastic wave propagation as a series of forward scattering problems, where the medium is described as a random distribution of scatterers of various sizes and physical parameters. Analytical results based on simple models compare well with numerical simulations for a wave propagating through a medium containing a random distribution of spherical scatterers. In another study, researchers developed a new coupled integral equation-differential equation approach for the nonlinear inversion of electromagnetic, seismic velocity and hydrologic conductivity data sets. New GILD and SGILD methods provide a high-resolution, robust and stable algorithm suitable for high-performance parallel machines.