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Development of Conceptual Geochemical Models
Published in William J. Deutsch, Groundwater Geochemistry, 2020
In addition to simulating the natural system, the forward method of geochemical modeling is appropriate to use in predicting the movement of contaminants and in remediation design. In the case of simulating contaminant movement, the conceptual model starts with the natural system in equilibrium between groundwater and reactive minerals in the aquifer. The addition of a contaminant to this system creates a disequilibrium that produces reactions that progress in a direction to reduce the disequilibrium, ultimately establishing a new equilibrium condition. The forward model predicts this new equilibrium and distributes the contaminant between the mobile groundwater phase and the immobile solid phases. For restoration design, various chemical techniques of treating the aquifer system or, for pump and treat methods, the groundwater alone can be simulated by the forward method. For instance, neutralization of an acidic groundwater or waste stream can be simulated by adding increments of calcite or some other neutralizing agent to the aquifer or water. Secondary reactions such as gypsum precipitation may also be included in these models. Forward modeling of neutralization allows estimates to be made of the amount of calcite required to neutralize the solution to a given pH value and the amount of byproduct solids formed. Models of restoration should be validated by laboratory experiments and small scale field tests. The most commonly used computer codes for forward-reaction modeling are MINTEQ7–9 and PHREEQE.10 The capabilities of these modeling codes are described in Chapter 5.
Geochemical assessment of fluoride enriched groundwater and health implications from a part of Yavtmal District, India
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Deepali Marghade, Deepak B. Malpe, N. Subba Rao, B. Sunitha
All the analyses were carried out in duplicate and the results were found reproducible within ±5% error limit. The accuracy of complete chemical analysis of a groundwater sample was checked by computing the cation–anion balance (CAB), as suggested by Domenico and Schwartz (1990). The CAB is found to be within the standard limit of ±5%. The statistical software package SPSS 18.0 for Windows was used to calculate Pearson’s correlation. In the geochemical modeling and saturation indices for the groundwater samples were carried out using PHREEQC (Parkhurst and Appelo 1999). The saturation indices are used to calculate the degree of equilibrium established between water and minerals phases. The saturation index (SI) is ratio of the ion activity product KIAP to solubility product KSP calculated as shown below:
Assessment of shallow groundwater quality and its suitability for drinking purpose near the Béni-Mellal wastewater treatment lagoon (Morocco)
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Ahmed Barakat, Abdessamad Hilali, Mohamed El Baghdadi, Fatima Touhami
According to regional geology, the calcite, aragonite, and dolomite minerals are considered as the possible major mineral phases for the geochemical modeling (Table 6). The obtained SI values are negative, ranging between –1.69 and –0.91, indicating thus that the water samples are undersaturated with respect to calcite, aragonite, and dolomite. This suggested that water–rock interaction had not reached equilibrium yet in groundwater in the study area, winch has a tendency to dissolve minerals.