A Case Study of the Effects of Oil Shale Operations on Surface and Groundwater Quality: II. Major Inorganic Ions
- T. R. Garland,
- J. M. Zachara and
- R. E. Wildung *
The distribution of the major inorganic ions in surface and groundwater, as related to substrata and hydrologic phenomena, was determined in a semiarid watershed representing an important area of oil shale development in northwestern Colorado. Surface and alluvial groundwaters were analyzed with time over a period of 1 yr, both upstream and downstream of an unengineered oil shale disposal site. These observations provided unique insight into the chemical and hydrologic controls on the composition of major ions in ground and surface waters. The primary dissolved species in the surface and groundwaters above and below the disposal site were Na +, Mg2+, Ca2+, SO2−4, and HCO−3. Increases in total salts in alluvial groundwaters below the disposal site were due primarily to Na + and SO2−4. Groundwaters above the disposal site were found to be in near equilibrium with calcite and dolomite; waters below the site were also in equilibrium with gypsum. Concentrations of the other ions measured all increased below the site, but elements lacking major solubility controls in calcareous soil and subsoil, i.e., K++, Li++, CL−, and NO−3, were most elevated. These solutes decreased in concentration down-gradient from the waste disposal area, but different phenomena controlled their behavior. Concentrations of HCO−3 in alluvial groundwater fluctuated seasonally (+20%), reflecting a combination of biological (microbial and root respiration) and mineral solubility (e.g., CaCO3) controls. Although the primary source of N to groundwater was NH+4-laden waste water, NO3 − constituted the major N species measured as a result of nitrification in the relatively aerobic groundwater system. Macroions indicative of the influence of the waste disposal site on surface water quality were CL−, K++, and Li++. Lithium could serve as a sensitive indicator of the presence of retorted shale leachate.
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