ex18: Example 18-Inverse Modeling of the Madison Aquifer

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In this example, inverse modeling, including isotope mole-balance modeling, is applied to the evolution of water in the Madison aquifer in Montana. Plummer and others (1990) used mole-balance modeling to quantify the extent of dedolomitization at locations throughout the aquifer. In the dedolomitization process, anhydrite dissolution causes the precipitation of calcite and dissolution of dolomite. Additional reactions identified by mole-balance modeling include sulfate reduction, cation exchange, and halite and sylvite dissolution (Plummer and others, 1990). Del 13C and del 34S data were used to corroborate the mole-balance models and carbon-14 was used to estimate groundwater ages (Plummer and others, 1990). Initial and final water samples were selected from a flow path that extends from north-central Wyoming northeast across Montana (Plummer and others, 1990, flow path 3). This pair of water samples was selected specifically because it was one of the few pairs that showed a relatively large discrepancy between previous mole-balance approaches and the mole-balance approach of PHREEQC, which includes uncertainties; results for most sample pairs were not significantly different between the two approaches. In addition, this pair of samples was selected because it was modeled in detail in Plummer and others (1990) to determine the sensitivity of mole-balance results to various model assumptions and was used as an example in the NETPATH manual (Plummer and others, 1994, example 6). Results of PHREEQC calculations are compared to NETPATH calculations. This example is also discussed in Parkhurst (1997). The example can be run using the phrRunString routine.





See Also

Other Examples: ex10, ex11, ex12, ex13a, ex14, ex15, ex16, ex17, ex19, ex1, ex20a, ex21, ex22, ex2, ex3, ex4, ex5, ex6, ex7, ex8, ex9



phreeqc documentation built on July 1, 2020, 11:46 p.m.