GEOCHEMICAL MODELING OF CONTROLS ON DISSOLVED AS, MN, AND FE IN THE DEXTER PIT LAKE, TUSCARORA, ELKO COUNTY, NEVADA
Current research is using geochemical data combined with hydrodynamics to model the controls on dissolved As, Mn, and Fe. Preliminary data analysis suggests that the dissolved concentrations of these elements are controlled predominantly by reductive dissolution, oxidative precipitation, and surface adsorption. Seasonal stratification develops during spring and summer and results in the formation of an oxidized epilimnion and a reduced hypolimnion. Annual overturn of lake water in early winter most likely results in the oxidative precipitation of dissolved Mn and Fe from the hypolimnion, which in turn removes As from solution through adsorption. Following this trend of decreasing dissolved concentrations, thermal and chemical stratification is again induced, causing subsequent increases in dissolved concentrations of As, Mn and Fe (from 6 to 17, 150 to 350, and 150 to 300 µg/L respectively) in the hypolimnion. This cycle occurred in both 1999 and 2000. Numerical modeling of the Dexter Pit Lake system will focus on quantifying the controls of adsorption and mineral precipitation reactions on the concentration of dissolved species. Modeling will use either PHREEQC or DYRESM-CAEDYM to link chemical and hydrologic processes and produce predictions of pit lake chemistry. Statistical analyses such as principal component analysis will also be applied to test for subtle trends in the data.