TY - JOUR
T1 - Resolving aquifer behavior near a focused recharge feature based upon synoptic wellfield hydrogeochemical tracer results
AU - Gentry, Randall W.
AU - Ku, Teh Lung
AU - Luo, Shangde
AU - Todd, Vincent
AU - Larsen, Daniel
AU - McCarthy, John
N1 - Funding Information:
This research was supported by the National Science Foundation (NSF) Grant EAR-0229208. The researchers are also appreciative to Arthur Vick at Memphis Light, Gas and Water for helping with access and set-up for production well sampling. Also, the researchers would like to express appreciation to the Ground Water Institute at the University of Memphis for providing access to sampling equipment and supplies for some of the field work associated with this project. In addition, the authors wish to express appreciation to the Tennessee District of the USGS, particularly Mr. Jack Carmichael, who collected the natural gamma-logs associated with the rotasonic drilling in the Sheahan wellfield.
PY - 2006/5/30
Y1 - 2006/5/30
N2 - Aquitard windows are known to occur in unconsolidated aquifer systems and represent areas of focused recharge to otherwise confined underlying aquifers. The study herein focused on a known window site affecting the Memphis aquifer located in the Sheahan wellfield in Shelby County, Tennessee. Uranium- and thorium-series radioisotopes were evaluated from production wells sampled in the wellfield and compared to other geochemical characteristics of the system. From the research, a conceptual model was realized whereby higher uranium concentrations from near-surface waters flow through a redox barrier in the aquitard window and become depleted in uranium. Further, 234U/238U activity ratio increased downgradient of the recharge source by alpha-recoil mobilization of 234U via 234Th, and possibly leaching of uranium bound by iron hydroxides via dissolution and subsequent precipitation by reducing waters flowing to downgradient wells. The behavior of the hydrogeochemical tracers could be best described in the conceptual model by normalizing uranium to Fe2+ throughout the system. The use of the [U]-[Fe2+] pair provides a useful tool for understanding of the mixing behavior near focused recharge sites with redox barriers and may be useful for developing aquifer behavior models.
AB - Aquitard windows are known to occur in unconsolidated aquifer systems and represent areas of focused recharge to otherwise confined underlying aquifers. The study herein focused on a known window site affecting the Memphis aquifer located in the Sheahan wellfield in Shelby County, Tennessee. Uranium- and thorium-series radioisotopes were evaluated from production wells sampled in the wellfield and compared to other geochemical characteristics of the system. From the research, a conceptual model was realized whereby higher uranium concentrations from near-surface waters flow through a redox barrier in the aquitard window and become depleted in uranium. Further, 234U/238U activity ratio increased downgradient of the recharge source by alpha-recoil mobilization of 234U via 234Th, and possibly leaching of uranium bound by iron hydroxides via dissolution and subsequent precipitation by reducing waters flowing to downgradient wells. The behavior of the hydrogeochemical tracers could be best described in the conceptual model by normalizing uranium to Fe2+ throughout the system. The use of the [U]-[Fe2+] pair provides a useful tool for understanding of the mixing behavior near focused recharge sites with redox barriers and may be useful for developing aquifer behavior models.
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U2 - 10.1016/j.jhydrol.2005.09.011
DO - 10.1016/j.jhydrol.2005.09.011
M3 - Article
AN - SCOPUS:33747418487
SN - 0022-1694
VL - 323
SP - 387
EP - 403
JO - Journal of Hydrology
JF - Journal of Hydrology
IS - 1-4
ER -