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Groundwater and Spring-water Quality

A subset of water samples from Tsezhin Bii' has the isotopic composition characteristic of the N-Aquifer, an important, regional groundwater source, and includes those that have the highest concentrations of arsenic. The arsenic concentrations and other variations in chemistry may be produced as a result of changes in sedimentary facies within the aquifer unit.

Seeps, which are springs during wetter periods, indicate where water supplies may have been available during the past. By mapping seeps as potential water sources, a new archaeological site in west Tsezhin Bii' has been located and included in site surveys. The remains are located in sand dunes, and pottery types may provide some age control on dune stratigraphy.

Geologic characterization of well and spring sites suggests that many aquifers are shallow and limited in extent, and therefore sensitive to over utilization and contamination. Devitrified ash may contribute to high pH in groundwater sources, providing a mechanism for the subsequent solubility and liberation of arsenic from iron-rich weathered sediment. Diatreme-related springs percolate through Fe-oxides associated with volcaniclastic sediments, and have high concentrations of arsenic in groundwater.

Initial interviews with elders have aided in locating springs for water sampling, and identifying areas undergoing rapid geomorphologic and ecological change.