Carbon dioxide pressure groundwater

Shuster, E.T. and White, W.B., 1972. Source areas and climatic effects in carbonate groundwaters determined by saturation indices and carbon dioxide pressures. Water Resour. Res., 8 1067—73. 

The dehalogenation of chlorinated compounds in groundwater results in increases in chloride ions. Increases in anions result in increases in cations through what is known as the common ion effect. Where calcium is the dominant cation, increases in chloride result in increase in calcium and hence carbon dioxide. This, in turn, increases the partial pressure of CO2, facilitating the removal of chlorinated DNAPL compounds. 

The pH of most groundwaters of interest to waste disposal is in the range 6-10 (Fig. 1). There are a number of factors which are important in governing the pH of groundwater reactions with minerals in the rock, particularly aluminosilicates such as feldspars, micas and clays the partial pressure of carbon dioxide (Fcoj) the concentration of so-called conservative or mobile ions such as chloride (Michard 1987) and temperature. Reactions with the rock mineralogy and dissolved carbon dioxide can affect pH through temperature-dependent equilibria such as ... 

PcOi, or the partial pressure of carbon dioxide, represents the activity or thermodynamic concentration of carbon dioxide in the aqueous phase. It is a parameter which is not measured directly in groundwaters without a coexisting gas phase, but is calculated from the following relationship ... 

Speciation calculations for the carbonate system using the alkalinity data and pH values after day 50 and plotted in Fig. 3, are consistent with C02(g) partial pressures ranging between 10" and lO atm. These values agree well with the values for carbon dioxide determined by gas chromatography of dissolved gases collected from water samples in boreholes at the site (Table 2). There is clearly a dominant source of carbon dioxide to the groundwater at the site, presumably microbial respiration or fermentation of organic carbon. 

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