Year: 2013
Type: dissertation
Abstract: The Sierra Nevada foothills in the South Yuba River basin Nevada County, \nCA is underlain by plutonic, metabasic rocks of pre-Tertiary age. Fifty-six water \nsamples from five sites were analyzed for spatial and temporal variations using stable \nisotopes of water and major element chemistry. Hydrogeochemical data from surface \nwater and groundwater indicate site specific, depth related spatial variations. Temporal \nvariations are evident in most surface water data and absent in most groundwater data. \nData for 18O and deuterium (D) plot close to the global meteoric water line confirming a \nmeteoric source and minimal subsequent evaporative fractionation or effects of gaswater- \nrock interactions. An altitude effect presented in surface and groundwater data as \na 0.1 per mil decrease in ?? 18O and a 0.5- 0.7 per mil decrease in ?? D per 30.5 meter (100ft) increase between 305 and 884 meters (1,000 and 2,900 feet) in elevation. Major \nelement chemistry was dominated by sodium, magnesium, and calcium bicarbonate in \ndilute concentrations. Most groundwater data had higher Ca/Na (1.8:1), Ca/Mg (4:3), and \nHCO3 \n- /Cl- (3:1) ratios than surface water data from the same site, indicative of local gaswater- \nrock interactions or mixing of infiltrating water with other groundwater sources. \nMost deep groundwater data (>91 meters or 300ft) had similar Ca/Na (0.9:1), and higher \nCa/Mg (1.6:1) and HCO3 \n- /Cl- (1.6:1) ratios than shallow groundwater data. Most \ngroundwater samples were under saturated or close to saturation with respect to calcite. \nAqueous speciation modeling, EQ3NR version 7.2c, adjusted for lab conditions, \nindicated acceptable charge balance relations. Most water data are consistent with \nfracture flow in the granitic and metamorphic rocks of the region. Data suggest a \nprecipitation dominated hydrologic regime where local surface waters are related to local \ngroundwaters, indicating that infiltration by way of secondary porosity contributes to \ngroundwater production in fractured rock.
Author: Evelyn Marie Soltero
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1617480858