If carbon dioxide stored in deep saline aquifers would leak into overlying sources of potable groundwater, the intruding CO2 would lower groundwater pH and thereby enhance the solubility of hazardous inorganic constituents (such as lead or arsenic) present in the aquifer minerals. How and to what extent groundwater quality would be affected depends largely on the initial abundance and distribution of these constituents in the aquifers, as well as on the aquifer mineralogy and the oxidation state. Using the USGS NWIS data base, we are conducting a systematic evaluation of more than 38,000 groundwater quality analyses from aquifers throughout the United States that report non-zero concentrations of selected hazardous constituents. The results of the evaluation are being employed to set up an equilibrium geochemical model of the aquifer chemistry in order to estimate the distribution of various constituents between the aqueous phase and adsorption and ion exchange sites, and in solid solution in primary and secondary minerals. Important qualitative conclusions can be drawn immediately from this evaluation regarding the geochemical vulnerability of the groundwaters. For example, the majority of the samples are saturated with respect to calcite, indicating that these groundwaters may somewhat buffer CO2-related pH changes. For quantitative evaluation, we use the equilibrium geochemical model as a starting point for reactive geochemical transport simulations that predict the impact of CO2 intrusion into a fresh- water aquifer and the related changes to the host rock mineralogy and water chemistry. The resulting concentrations of hazardous constituents in the groundwater are then compared to the EPA specified health- based limits for drinking water. Various sensitivity studies are conducted for different hydrological and geochemical and mineralogical conditions, representative of some major aquifer systems in the United States. Our findings help to understand (1) which aquifer systems and regions of the country might be vulnerable in case of CO2 intrusion, and (2) which inorganic constituents might adversely affect water quality and to what extent.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1009 Geochemical modeling (3610;
- 1806 Chemistry of fresh water;
- 1831 Groundwater quality