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Arsenic Hydrogeochemistry in an Irrigated River Valley—A Reevaluation
Author(s) -
Nimick David A.
Publication year - 1998
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1998.tb02191.x
Subject(s) - arsenic , groundwater recharge , groundwater , aquifer , hydrology (agriculture) , irrigation , leaching (pedology) , arsenic contamination of groundwater , sediment , soil water , geology , environmental science , alluvium , soil science , chemistry , geomorphology , agronomy , geotechnical engineering , organic chemistry , biology
Arsenic concentrations in ground water of the lower Madison River valley, Montana, are high (16 to 176 μg/L). Previous studies hypothesized that arsenic‐rich river water, applied as irrigation, was evapoconcentrated during recharge and contaminated the thin alluvial aquifer. Based on additional data collection and a reevaluation of the hydrology and geochemistry of the valley, the high arsenic concentrations in ground water are caused by a unique combination of natural hydrologic and geochemical factors, and irrigation appears to play a secondary role. The high arsenic concentrations in ground water have several causes: direct aquifer recharge by Madison River water having arsenic concentrations as high as 100 μg/L, leaching of arsenic from Tertiary volcano‐clastic sediment, and release of sorbed arsenic where redox conditions in ground water are reduced. The findings are consistent with related studies that demonstrate that arsenic is sorbed by irrigated soils in the valley. Although evaporation of applied irrigation water does not significantly increase arsenic concentrations in ground water, irrigation with arsenic‐rich water raises other environmental concerns.