What is the consequence when groundwater becomes saturated with CaCO3 in terms of limestone dissolution?

• A. Dissolution ceases as saturation is reached
• B. Dissolution accelerates despite saturation
• C. CO2 is released rapidly increasing dissolution
• D. Porosity increases dramatically with saturation

Answer: (A)

When groundwater becomes saturated with CaCO3, the water is in equilibrium with calcite. This means the amount of dissolved calcium carbonate cannot increase without changing conditions. The dissolution of limestone proceeds until the solution reaches the calcite solubility limit, at which point the forward dissolution rate balances the backward precipitation rate and there is no net dissolution. In other words, the system has no driving force to dissolve more limestone unless conditions shift (for example, more CO2 dissolving to lower pH, or changes in temperature or pressure). CO2 is consumed during dissolution, not released, which is why the idea of rapid CO2 release increasing dissolution is incorrect. Porosity can increase if dissolution continues, but once saturation is reached, further dissolution ceases, so porosity does not continue to rise solely because saturation has been attained.