Simulating the Porosity Reduction in a Permeable Reactive Barrier–Aquifer System Using THMC Software
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis study examines the use of THMC (Thermo-Hydro-Mechanical-Chemical) software to simulate porosity reduction in permeable reactive barrier (PRB) aquifer systems. The authors developed a numerical model that combines multiple physical processes to model chemical precipitation and particle deposition, which leads to PRB clogging over time. The model provides long-term performance predictions by considering both reactive transport and porosity change. The results indicate that PRB effectiveness decreases significantly over time, necessitating maintenance/rehabilitation.
The application of THMC software to PRB systems has limited examples in the literature. In this respect, the application area presents a novel element.
Focusing on the temporal evolution of porosity reduction through multi-process (THMC) modeling is a unique approach. However, the modeling approach and software used have been used in various hydrogeological scenarios and are therefore not entirely new.
It has the potential to contribute to maintenance planning and long-term performance assessment in PRB design. Porosity changes are modeled in detail using multi-process integration (hydraulic, mechanical, chemical).
Practical engineering implications regarding how PRB performance changes over time are presented.
Major Revision
1. Field data is limited – No comprehensive field study was presented for model validation, leaving the model's reliability partially uncertain.
2. Parameter sensitivity analysis is incomplete – The effect of model inputs on the results was not systematically tested.
3. No alternative model comparison – No performance comparison was made with modeling approaches other than THMC.
4. Some of the images are low resolution, and axis legends are inadequate.
5. The extent to which the model's boundary conditions and assumptions match field reality is not adequately discussed.
6. The overall technical language is appropriate, but some sentences are long and complex.
7. The text flow is occasionally disjointed, and linking sentences are needed at section transitions.
8. Figures and tables should be presented at higher resolution and with detailed explanations.
Overall Assessment
The study is publishable with appropriate revisions. However, significant improvements are needed, particularly in model validation, field data utilization, and parameter sensitivity analysis.
Recommendation: The authors should strengthen both methodology and presentation.
Major Revision
Author Response
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Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper: Simulating the Porosity Reduction in a Permeable Reactive Barrier-Aquifer System Using THMC Software describe the application of THMC model for evaluation of the mechanisms driving porosity reduction in PRB containing ZVI, focusing on mineral fouling. The introductory part of the paper describes well the issue of porosity reduction in PRB systems by the formation of minerals, due to chemical reactions. Although the goal and purpose of the work are clearly stated in this paper, they are not adequately and unambiguously substantiated in the manuscript. Namely, based on what has been presented, one does not get the impression that the authors have fully considered the dynamic nature of chemical reactions, that is, the rate of chemical reactions. The assumptions in the model seem unrealistic and inapplicable in practice, especially in terms of modelling a homogeneous and isotropic aquifer, which is a rare case in nature. In fact, the applicability of the obtained results in real aquifers and real PRB systems is not clear. Furthermore, from the presentation of the obtained results, as well as the discussion, it is not possible, at least not completely, to check all the assumptions in the model, as well as the reliability of the applied conceptual model. I suggest that the paper in this form is not accepted for publication. Authors are suggested to thoroughly change the methodological framework and the presentation of the obtained results. Specific remarks follow below.
In the introduction of the paper, it is stated that THMC modelling was adopted in this study as a more robust alternative, eliminating the constraints of RT3D and enabling a more precise prediction of porosity reduction. These claims are not supported by comparisons of simulation results using the used software and other similar software, so it is only an assumption and not a proven claim.
Line 119-129 – these general notes on the application of THMC software are more suitable for an introductory chapter. In this chapter, emphasis should be placed on conceptual model development, parameter selection, boundary conditions, and processes that need to be simulated to achieve the modelling goal.
Line 121-122: You have conducted your simulation in homogeneous aquifer with consistent hydraulic conductivity. In the discussion or conclusion, assess the limitations of this approach, obtained results and applicability for a real heterogeneous and anisotropic aquifer.
Line 140: One of the assumptions you introduced in the development of the conceptual model is that an investigated aquifer is considered in chemical equilibrium before entering the PRB, meaning no reactions occur. It is necessary to determine the baseline condition of the chemical concentrations in the groundwater, based on the real/assumed mineral-petrographic composition of the simulated aquifer, and then carry out a simulation of chemical reactions.
Line 142: „The groundwater entering the PRB is thought to include Fe2+, DO, Mg2+, Ca2+, Mn2+, SO4 2- , CO3 2- , H+ , OH- , NO3 - , and HCO3“ – To determine the composition of groundwater entering the PRB (natural variations of chemical composition during the hydrological year), it is usual to model the equilibrium or kinetic chemical reactions in aquifer under natural conditions, i.e. definition of baseline conditions of chemical composition.
Line 143-145: „The soluble substances in the groundwater will react with ZVI to form nine minerals: CaCO3, 144 FeCO3, MgCO3, CaMg(CO3)2, Fe(OH)2, FeS, Mn(OH)2, MnCO3, and Mg(OH)2“ - Based on what evidence or assumptions did you predict the formation of these nine minerals?
Line 146-148: “Instead, the purpose was to determine which features were necessary to include when modelling how mineral fouling influences PRB performance.“ - The sentence is not clear. Are you referring here to sensitivity analysis of model parameters or something else? What kind of features are you talking about here?
Line 187 - Background groundwater concentrations were assigned to the upgradient concentration boundary, which was considered geographically and temporally uniform - this assumption is not correct, since transient flow simulation is clearly stated in line 165. Furthermore, it is known that background concentrations of substances in ground water are defined as interval values due to variability of hydrodynamic and hydrogeochemical condition in aquifers. In other words, it is not clear how the background concentrations in Table 2 were defined.
It is known that to predict chemical reactions, it is necessary to know the oxidation-reduction states in the simulated aquifer, pH, temperature and other chemical-physical properties that affect the rate of chemical reaction. In addition, the rate and model of chemical reaction depend on the initial concentrations of reactants and vary in time. Considering the variability of the rate of chemical reactions and its strong dependence on the initial concentrations of chemical substances, it would be valuable to consider a possible change of initial concentrations of chemical substances in respect of dynamic nature of rate of chemical reactions.
Comments on the Quality of English Languageno suggestion
Author Response
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Reviewer 3 Report
Comments and Suggestions for Authors- For the introduction section: the first paragraph should be brief to illustrate the research background and research topic. For the following several paragraphs, authors should review the reach progress over the world regarding present research topic.
- Research objective should be pointed out in the last paragraph of introduction section. The specific aims are should be included in the last paragraph.
- Did authors refer to some field cases in the research, at least for the simulating conditions setting?
- The results and discussion section is too simple and not enough to provide details and evidences. This part should be reorganized and improved.
Author Response
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Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsCorrections and responses have been provided by the authors, including my evaluations and criticisms.
Author Response
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Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors have significantly revised their manuscript and it can be accepted for publication.
Comments on the Quality of English LanguageThe manuscript requires English language editing
Author Response
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Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript has been greatly improved in last round, but need to reorganize the conclusions section. Suggestions are as below:
The conclusions section needs further refinement. It should focus solely on significant and important results and findings, omitting minor details. Additionally, this section should be presented in an objective, descriptive manner.
Author Response
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