2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 20-8
Presentation Time: 10:05 AM

STATISTICAL AND SPATIAL ANALYSIS OF INORGANIC ANIONS, CATIONS AND RADIONUCLIDES IN CALIFORNIA’S GROUNDWATER: ESTABLISHING A BACKGROUND AND ANALYZING SPATIAL VARIABILITY


RENSHAW, Andrew M.1, MORAN, Jean E.1, ESSER, Brad K.2 and BIBBY, Richard K.2, (1)Department of Earth and Environmental Sciences, California State University, East Bay, 25800 Carlos Bee Boulevard, Hayward, CA 94542-3088, (2)Chemical Sciences Division, Lawrence Livermore National Laboratory, L-231, POB 808, Livermore, CA 94551, arenshaw06@gmail.com

California’s regional geological environments, such as aquifers with a granitic basement or sedimentary basins with oil reservoirs, constrain the groundwater’s chemical composition. The geological complexity of California generates aquifer systems that contain a wide range of sediments, recharge mechanisms, dissolved oxygen quantities and additional regional to sub-regional geochemical differences. A spatial analysis of ten hydrologic regions provides regional average distributions of chemical constituents with respect to mixing of deeply sourced waters associated with organic sedimentary deposits and shallow groundwater used for drinking water supply. In addition, the analysis provides a representation of the patterns in background concentrations that could aid in the determination of anthropogenic effects on groundwater chemistry, including oil and gas production.

The statistical and spatial analysis was conducted through inputting and interpreting a large query of supply well data into a geographic information system data frame. The primary constituents of interest are radionuclides: radium and radon and related anions and cations. Sedimentary organic deposits typically contain high concentrations of naturally occurring radioactive materials, such as 232Th and 238U. Furthermore, groundwater that interacts with the sedimentary organic deposits generally has high activities of 232Th and 238U decay products 228Ra and 226Ra. Previous studies have indicated that the ratio of 228Ra/226Ra in groundwater correlates with the ratio of 232Th/238U in the aquifer materials providing evidence for the source of radium in groundwater. Comparing the hydrogeologic setting and the groundwater chemistry demonstrates the usefulness of the 228Ra/226Ra ratio in the determination of the mixing of groundwater between deep-seated aquifers with shallow drinking water supply aquifers. Establishing a background database of certain anions, cations and radionuclides associated with sedimentary organic material will provide local, regional and state authorities and water-resource managers with information that could prove useful when examining future effects of conventional or non-conventional energy resource development.

Handouts
  • Renshaw_GSA_2014_FINAL_JEMed.pdf (16.5 MB)