Spatial variability in sources of groundwater salinity may exist due to stratigraphic, geochemical, and hydrologic processes even in an integrated and relatively homogeneous aquifer system. For this reason, characterization methods are needed to determine salinity sources, flow, and transport in alluvial/fluvial groundwater basins. Geochemical tracers analyzed from groundwater samples were used to determine the sources of salt contributing to groundwater beneath the southern Rio Grande flood plain of the Mesilla basin located in southern New Mexico and west Texas. Results from southern Mesilla Valley groundwaters show a localized plume of saline groundwater (10,000-29,700 mg/L total dissolved solids) near Sunland Park, NM. δ34S signatures of groundwater within the plume (+12.36 to +12.46‰) are comparable to δ34S signatures of Permian gypsum (+12.5‰) suggesting prolonged contact between groundwater and underlying Paleozoic bedrock. Above atmospheric concentrations of 39Ar (132-134% pM) and 4He (10-6 to 10-7 ccSTP/g(H2O)) in groundwater from the plume, confirm a significant fraction of the groundwater is old (>1,000 years). North of Sunland Park, NM, decreasing groundwater salinity is coexists with a spatial transition from sedimentary to volcanic rock underlying the alluvial aquifer, increasing alluvial sediment thickness, and δ34S signatures of groundwater (+2.28 to +5.76‰) which cannot originate from Paleozoic bedrock. These results suggest a decreased influence of upward flow from sedimentary bedrock and increased dilution of brackish groundwater within the lower salinity alluvial aquifer in the central and northern Mesilla Valley. This study illustrates how nested well clusters and geochemical tracers can be used to identify salinity sources and processes in geochemical investigations.
|Advisor:||Carroll, Kenneth C.|
|Commitee:||Witcher, James C., Ramos, Frank|
|School:||New Mexico State University|
|Department:||Water Science and Management|
|School Location:||United States -- New Mexico|
|Source:||MAI 81/2(E), Masters Abstracts International|
|Subjects:||Hydrologic sciences, Geochemistry|
|Keywords:||Texas, Mesilla basin, New Mexico|
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