| Aqueous Geochemistry of the Pueblo Colorado Wash Aquifer Pandamouz, A., Ort, M. H., Breit, G. N., Hiza, M., and Parnell, R. A. American Geophysical Union Fall Meeting Abstract, 2005. |
Pueblo Colorado Wash alluvial aquifer, located in northeastern Arizona on the Navajo Nation, is about 20 km long and 2-5 km wide and formed by infilling a canyon as deep as 70 m in Mesozoic and Tertiary sedimentary rocks. This aquifer is the main source of drinking water for many Navajo communities. The composition of shallow water (<20 m) in the aquifer contrasts with that from deeper parts. The shallower water is distinguished by low specific conductance (<1 mS cm -1 ) and higher dissolved oxygen, while the deeper parts have a wide range of values for specific conductance (<1-22 mS cm -1 ) and low dissolved oxygen. Some wells (deeper water) are sulfate dominant whilst most springs and shallow wells (shallow water) are bicarbonate dominant. A comparison of two datasets-one from 1960's, and the other from the current study started in 2004-shows that the concentration of ions, such as Cl - and SO 4 2- , in the water from some wells is much higher in samples taken in 2004. High concentrations of SO 4 2- , Cl - , F - , K + , Ca 2+ , Na + , and Mg 2+ in different wells and springs follow no apparent spatial trends. d 13 C data have a wide range, from -3.4 in shallow water to -11.7 in deep water. The low d 13 C values along with the high dissolved Fe, Mn, and Ba in some wells and springs are consistent with microbial respiration in the aquifer. The d 18 O and d D show that the shallow water has experienced varying amounts of evaporation. The differences in water composition reflect the heterogeneity in the alluvium and older formations surrounding the aquifer, and the role of water-sediment interactions in the water composition. Temporal increases in salinity are attributed to decreased rainfall and increased withdrawal of water for domestic supplies. Results highlight the sensitivity of water quality in small aquifers to climate shifts and development. |
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