Thesis (M.Sc.Eng.)-University of Natal, Durban, 1973. / Full text also available online. Scroll down to electronic link.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 70-74). Also available in electronic version. Access restricted to campus users.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.140-163).

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Not available / text

Anomalous concentrations of silica in ground water of the eastern San Joaquin Valley originate from several diverse sources and are subsequently modified by recharge or diagenesis. Statistics, geochemical models, and column studies identified potential sources of silica in ground water and those parameters most important in influencing its distribution. Principal components analysis indicated inverse time and potassium as the parameters which best relate to silica. Inverse time relates to ground-water recharge while potassium relates to either the rhyolitic Friant Pumice, the hardpans of the eastern San Joaquin Valley, or diagenetic losses. A lumped parameter model suggests that recharge is responsible for the drop in silica concentrations beneath Fresno since 1971. The Madera County model indicates higher silica concentrations associated with the Friant Pumice, older geologic units with hardpans, finer grained sediments, and areas of ground-water discharge. Lower silica concentrations are associated with unweathered sediments, areas receiving recharge, and areas underlain by the Corcoran Clay. Column leaching studies produced silica concentrations from the Friant Pumice of up to 90 mg/1, Turlock Lake and Riverbank Formation hardpans from 40-50 mg/1, and younger Modesto Formation sediments from 10-40 mg/l. Spatially, volcanogenic sediments impart the highest silica concentrations to the ground water, 70-95 mg/1, and occur along the eastern margin of the valley, north of the San Joaquin River, or in San Joaquin River fluvial deposits. Iron-silica hardpans, found at various depths along the east side of the valley, are associated with silica concentrations of 40-70 mg/l. The typical arkosic sediments of the eastern valley have silica concentrations of 20-40 mg/l. Silica concentrations in ground water are modified by recharge and diagenetic processes. Either natural or artificial recharge having 4-16 mg/1 silica may lower ambient silica concentrations in ground water. Recharge occurs beneath some rivers and in transmissive paleochannel deposits; artificial sources include agricultural overirrigation and basin recharge. The down-gradient loss of silica to the sedimentary column, more prevalent at depth, apparently is by the sorption of silica on clays, the formation of clays, or deposition of amorphous silica.

The usefulness of stable isotopes of dissolved sulfate (δ₃₄S and δ₁₈O) as well as sulfate concentration was evaluated in four cases of study in southern Arizona. In Tucson basin, they have been used to determine the sources of sulfate in the groundwater, to delineate groundwater flow paths and recharge process, and to identify the groundwater domain. In Sonoita Creek near Patagonia, in combination with hydrochemical analysis and other environmental isotopes they were used to identify the sources of sulfate in the groundwater and surface water, the groundwater residence time, the interaction between groundwater and surface water, and the sources of base flow in Sonoita Creek. In the Patagonia Mountains, they were used to investigate the oxidation mechanisms of sulfide minerals. In evaporite deposits, δ₃₄S and δ₁₈O were used to determine the sources of sulfur, and to estimate the contribution of different S sources. This work shows that δ₃₄S and δ₁₈O of sulfate are excellent tracers of sulfate sources in groundwater, surface water, acid mine drainage and evaporite deposits in southern Arizona. The distinctive isotope compositions of the sulfur sources permit a clear identification of sources in aqueous environment, and quantification of the contribution from respective sources in one case. The results demonstrate the lithospheric origins of sulfur in the aqueous environment and evaporite deposits, and with Permian evaporite the most important source of sulfate.

No description available.

No description available.

No description available.