title: Shallow Groundwater Conveyance of Geologically Derived Contaminants to Urban Creeks in Southern California.
abstract: In California alone, there are currently over 200 instances on the EPA's list of impaired water bodies with unknown sources of excessive salinity or trace contaminants. This investigation focuses on Orange County, CA, a region that has undergone extensive hydrological modification, relies heavily on imported water for municipal supply, and has come under regulatory scrutiny for elevated TDS, sulfate, Cd, Ni, and Se. A survey of shallow groundwater weeps and springs, discharging directly to urban creeks, reveals high concentrations of TDS, sulfate, Cd, Ni, Zn, Cu, and Se that are often far in excess of water quality standards. Isotopic (δ(34)S and δ(18)O) and geochemical evidence indicate that the source of sulfate and TDS is weathering of sulfide minerals in the Capistrano Formation marine mudstone and dissolution of secondary minerals formed during past periods of sulfide oxidation, rather than anthropogenic inputs. The relative availability of carbonate minerals along the flow path appears to control pH, which then influences trace metal mobility to surface waters. Stable isotopes of H2O indicate that despite widespread use of imported water, meteoric recharge dominates shallow groundwater inputs with municipal sources contributing only 13-29% of discharge. These findings highlight the importance of understanding the hydrogeological setting to properly apportion contaminant sources and conveyances.
authors.affiliation: †Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, United States.
authors.forename: Audra I
authors.initials: AI
authors.lastname: Bardsley
authors.affiliation: †Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, United States.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Hammond
authors.affiliation: ‡OC Watersheds, County of Orange Public Works, 2301 Glassell Street, Orange, California 92865, United States.
authors.forename: Theodore
authors.initials: T
authors.lastname: von Bitner
authors.affiliation: †Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, United States.
authors.forename: Nikolaus H
authors.initials: NH
authors.lastname: Buenning
authors.affiliation: §Department of Earth System Science, University of California, Irvine, California 92697, United States.
authors.forename: Amy
authors.initials: A
authors.lastname: Townsend-Small
mesh_terms: D002140:California; D004784:Environmental Monitoring / Q000379:methods; D005844:Geology; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007554:Isotopes / Q000032:analysis; D008670:Metals / Q000032:analysis; D054712:Salinity; D013431:Sulfates / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D007554:Isotopes; D008670:Metals; D013431:Sulfates; D014874:Water Pollutants, Chemical