HR: 0830h
AN: H51C-1047    [PDF]
TI: Tracking River Recharge in the Central Valley of California Using Chemical and Isotopic Tracers
AU: * Moran, J E
EM: moran10@llnl.gov
AF: Lawrence Livermore National Laboratory, L-231, P.O. Box 808, Livermore, CA 94550
AU: Hudson, B
EM: hudson5@llnl.gov
AF: Lawrence Livermore National Laboratory, L-231, P.O. Box 808, Livermore, CA 94550
AU: Evans, D
EM: dave-evans@csus.edu
AF: Department of Geology, California State University at Sacramento, 6000 J St., Sacramento, CA 95819-6043
AU: Horner, T
EM: hornertc@csus.edu
AF: Department of Geology, California State University at Sacramento, 6000 J St., Sacramento, CA 95819-6043
AU: Leif, R
EM: leif1@llnl.gov
AF: Lawrence Livermore National Laboratory, L-231, P.O. Box 808, Livermore, CA 94550
AU: Eaton, G F
EM: eaton3@llnl.gov
AF: Lawrence Livermore National Laboratory, L-231, P.O. Box 808, Livermore, CA 94550
AB: Recharge to alluvial aquifers along the major rivers of the Central Valley of California is influenced by human activity in adjacent urban areas and groundwater basins. Intense pumping of Central Valley aquifers may induce recharge, while slurry walls, emplaced for flood control in densely populated areas, are intended to protect levees by preventing shallow recharge. These large rivers carry distinct chemical and isotopic signatures that allow recent recharge to be traced in adjacent wells. In particular, stable isotopes of oxygen delineate areas where river water, carrying a depleted isotopic signature from Sierra Nevada precipitation (-11 to -15 per mil), is recharging groundwater aquifers where local precipitation is significantly heavier (-7 per mil). Trace anthropogenic compounds present in river water, such as MtBE (from precipitation and recreational boating on watershed reservoirs), are also useful for identifying areas where river water has recently infiltrated. Analysis of groundwater age, using the tritium-helium method allows estimation of the time since recharge, and evaluation of the effect of human activity on the natural groundwater recharge and flow patterns. Results from a detailed study along the American River in Sacramento, where a slurry wall is in place, show areas of recent recharge, as evidenced by relatively high MtBE concentrations (matching river concentrations) and young groundwater ages in shallow wells. In other wells, older ages and very low MtBE concentrations delineate areas where active recharge is not taking place. These results are interpreted in the context of basin-wide analyses for the Sacramento urban area, where most groundwater sampled from municipal wells is devoid of tritium, and therefore recharged more than about 50 years ago. These data are collected for the Ambient Groundwater Monitoring and Assessment (GAMA) program, sponsored by the CA State Water Resources Control Board. Oxygen isotopes indicate that American River water has recharged a large portion of this basin, with wells showing decreasing fractions of isotopically depleted water moving away from the river to the north. A similar pattern is observed in other areas of intense pumping in groundwater basins along the major rivers in the Central Valley. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting