Study on Numerical Simulation of Reactive-Transport of Groundwater Pollutants Caused by Acid Leaching of Uranium: A Case Study in Bayan-Uul Area, Northern China
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript describes the development and application of a multicomponent reactive transport model to evaluate the implication of in-situ leaching in a uranium mining district of Northern China. While the model development is not novel itself, as claimed by the authors (there are several 3D models of uranium mobility around), the experimental results are of interest for the journal’s readership. The attempt to model them numerically is also laudable, given the well-known difficulties when simulating real-life, operational-scale problems.
However, the manuscript cannot/should not be published in its present form. It requires major revisions and attention by the author regarding several technical and non-technical aspects. While reading, I detected several flaws, some of them listed below (not in order of importance, but rather annotated orderly while re-reading the manuscript):
- English language has severe flaws. Grammar-wise, the manuscript should be proofread by a native English speaker or professional editor. For instance,
o Line 43-44 reads “Although some reactive transport models (RTM) have been built to predict fluid flow.” Incomplete sentence.
o L47-48 “The three dimensional reactive transport models(3DRTM) .. has not been built” should be rewritten as “A three dimensional reactive …”. A native speaker would simply see such small details which render the reading smoother.
- The technical writing is quite inaccurate. Some sentences either make no sense, are too complex or meaningless. Just a few examples from the introduction:
o L56-58 “Among them, hydraulic capture is a simple, effective, and widely used pollution control method, which is used to control the oil pollutants diffusion [17], and optimize the number, location, and structure of pumping wells [18-21].”. This sentence is just meaningless: hydraulic capture is not used to control “diffusion” (in a hydrogeological context, this term has a well-defined connotation linked to a transport process) and is not used for optimization!
o L59-61 “With the development of numerical simulation technology, hydraulic capture methods were adopted to control the effect of pollutant migration combined with MODFLOW and MT3D [22].” This sentence is confusing.
o L61 “These methods are especially suitable for well-group production scenarios” . What does this mean?
o [I stop here; the list can continue basically to the end of the paper].
- No reference to any previous studies on the site has been made. Is that such a perfect unexplored area (a green field)? I do not think so: a quick Google Scholar search provides interesting recent papers on the same area (maybe not exactly the same site, but the geology should be the same). E.g.,
o Wang et al (2022) JH https://doi.org/10.1016/j.jhydrol.2022.128634
o Wang et al (2023) JH https://doi.org/10.1016/j.jhydrol.2023.130234
- In the abovementioned papers, the authors provide some information about the local geology and the experimental and modeling analyses carried out in that research are also based on ISL. It is important to compare the findings from this study with those previously made by other researchers in the same area.
- Figure 2 seems to provide a different hydrogeological setup than the setup reported by Wang et al.: why?
- The authors should report and discuss with greater detail the calibration process. Aspects that should addressed include:
o What is the spatial scale of the model? What is the scale of figures 3 and 4?
o Can you provide some reference of the site’s elevation? The head levels in
o Provide details of the resulting mesh. How many elements, what average size of the elements. Is Figure 4 representative of the actual mesh used in the model?
o Were all model parameters calibrated manually?
o The calibration plots show an extremely good match between observed and simulated pH and sulfate loadings. If the whole model parametrization is physically and geochemically homogeneous, what parameters were changed to achieve such result?
o No sensitivity analysis to any calibrated parameter was presented!
o There is a strong difference between the experimental pH in W1 (gets very acidic!), and W2 and W3, which remains at pH=5-6. What is controlling this effect? Is the pH buffered by some secondary mineral? Maybe gypsum? Notice that W1 observations reveal a small step around time 0.05 right at pH=5-6. Would be good to report the time evolution of the Saturation Index of this mineral on top of figures 4,5 and 6.
o Gypsum k25 is very high! Why not setting it as in equilibrium? Such a high value may give rise to strong numerical instabilities.
- The results and analysis of the simulated scenario cannot be properly assessed until the model implementation and calibration is properly presented.
- Providing Figure 10 and 11 is confusing, as the pH seems homogeneous while H+ concentrations seem not (matter of scales).
- There are some problems with the list of citations and corresponding cross-referencing in the text. For instance, refs. [23, 24] have nothing to with the works by Xu et al. which refer to Tough-React. Carefully check the list.
Comments on the Quality of English LanguageInsufficient. I urge the authors to proofread the text with the aid of a native English speaker or professional editor.
Author Response
Thank you very much!Your guidance and comments have significantly improved our manuscript.We have carefully revised the manuscript.Here is our revised manuscript and our response to your comments.Please review it. Thank you!
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
The title is misleading because this manuscript is not about research into contamination introduced into groundwater by ISL of uranium. Rather, the article is about reactive solute transport modeling. In this respect, however, the article offers nothing new, but shows first of all that the authors are not well versed in this area. In any case, it is urgently recommended that the title be changed. Some further problems and deficits are addressed below.
In the abstract authors mention that ”… some toxic and harmful substances might be produced”. This is rather vacuous. Authors should be more specific. Ra and Rn are probably the most dangerous elements; but others as well. Furthermore, authors introduce in the abstract a new abbreviation “3DRTM” which does not make sense and will do not make it into the technical literature. Authors try then to explain that pumping ratio and non-uniform injection schemes will minimize groundwater pollution. However, the abstract does not succeed at all and it is recommended to rewrite the abstract from scratch.
In the introduction authors mention that “some radioactive elements and heavy metals can enter groundwater and cause groundwater pollution”. Please be more specific (see abstract) and regarding the term “heavy metals” if authors use this more or less meaningless term they have to define this word (see Duffus 2002 IUPAC paper http://old.iupac.org/publications/pac/2002/pdf/7405x0793.pdf) or do not use it. Trace elements or toxic elements might be more suitable terms.
In the following, the authors attempt to formulate something about modeling in the field of ISL in the Introduction and mention the GMS system and Modfow with MT3D in this context. Of course, neither GMS nor Modflow with MT3D offer an even remotely useful approach here and should therefore not be mentioned at all or only marginally as unsuitable.
On contrary many 3d reactive transport models exist and are used since many years: e.g.
PHAST - A Computer Program for Simulating Groundwater Flow, Solute Transport, and Multicomponent Geochemical Reactions
PHT3D: A Reactive Multicomponent Transport Model for Saturated Porous Media
FEFLOW Plug-in piChem
Of course TOUGHREACT V4.13-OMP is as well a powerful system. But, which system is best suited for this case study can only be discussed if all systems are considered (not only those 4 mentioned by me here as examples).
With regard to the description of the aquifer, there is no indication that sandstones are generally classic dual porosity aquifers and therefore flow and transport take place both on fractures and in pores. This is an additional challenge, particularly with regard to the geochemical processes, and makes the results appear dubious.
With regard to table 1, the question arises as to why the gas phase plays a role in this case and therefore appears in the table.
Line 142 ff refers to capillary pressure calculation. Why is this important for the groundwater model presented?
Tab 2 and the accompanying text are very sparse in terms of relevant data. No nitrate in the groundwater? Why are the sulphate levels so high? No temperature, pH value, no oxygen concentration and no redox potential? Why not values for Fe-2 and Fe-3? Why not values for As-3 and As-5 as indicators for the redox conditions in the groundwater? A halfway reliable geochemical modeling is absolutely impossible for the solution of uraninite in the ISL system.
What was the nature of the injection solution (pH value?, composition?, oxidizing agent?, oxygen content?)?
How were the values in table 3 determined?
How were the minerals listed in table 5 selected? How were the parameters listed there determined? Experimentally (in which case the description of the methods is missing) or are they literature values (in which case the citations are missing)? In addition, the question arises as to whether these values are representative. Why pyrite does not have parameters for base and acid mechanisms?
Fig. 13 is completely incomprehensible and cannot be understood by reading the text. Head and z-value does not fit to each other. What is the message of this figure?
Finally, please be consistent using upper and lower case.
Comments on the Quality of English Languageneeds minor polyshing
Author Response
Thank you very much! Your guidance and comments have significantly improved our manuscript. We have carefully revised the manuscript. Here is our revised manuscript and our response to your comments. Please review it. Thank you!
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for giving me the chance to review this study. Some minor flaws exist in the research approach and the results reported in the current manuscript version. Therefore, I would like to recommend this manuscript be returned to the authors for minor revisions, as suggested below, before publication in the journal.
Title: Consider modifying it as more focused on groundwater pollution caused by in-situ leaching uranium
Keywords: Limit keywords up to 3-4, use appropriate ones, the words already used in the article title should not be repeated in keywords.
Lines 68-70: Have you considered the potential impact of other minerals besides calcite, pyrite, hematite, and uranium minerals? Exploring the influence of additional minerals could provide a more comprehensive understanding of the hydrogeochemical processes.
Lines 70-75: Did you encounter any challenges or limitations while building the three-dimensional reactive transport model (3DRTM) using TOUGHREACT? Discussing any difficulties faced and how you addressed them would add depth to your research.
Lines 164-165: That's fascinating! The use of the TOUGHREACT simulator in building the numerical model for the reactive transport of the mining area is impressive. It's amazing how this simulator allows for the inclusion of multiple mineral components and water-rock interactions in the model. Great job on incorporating such advanced technology into your research
Lines 168-170: How did you determine which mineral components to include in your numerical model? Did you focus on specific minerals that are commonly found in mining areas, or did you consider a broader range of minerals?
Line 171: In what ways do you think the inclusion of reactive geochemistry in the TOUGHREACT simulator enhances the accuracy and realism of the simulations compared to traditional hydrological models?
Lines 210-212: Finding the optimal pumping ratio and non-uniform injection ratio is key. I'm curious, in your study, how did you determine the best mining scheme for pollution control? Did you analyze the water table contour, streamline, and concentration breakthrough curve at W1?
Lines 252-253: I recommend you can create a flowchart to represent the principle of pollution control based on streamlined analysis, as described in your text.
Line 260: That's a great point! Sensitivity analysis is a valuable tool for determining the parameter that has the most significant influence on the dependent variable. The sensitivity coefficient helps us understand how much the dependent variable is affected by changes in an independent variable.
Line 295-300: Explain the significance of the findings: After mentioning the high concentration of SO4 2- and the migration distance, it would be beneficial to explain why these findings are significant or what implications they have for the acid-leaching process.
Line 450-455: Those simulation results about the pumping ratio and non-uniform injection ratio are really fascinating. Finding that a non-uniform injection ratio of 0.1 is the most beneficial for creating the hydraulic capture zone is quite valuable information. It's great to see researchers like you uncovering these insights to help manage groundwater pollution.
References: Include maximum latest citations in the manuscript,
Comments on the Quality of English Language
English is fine
Author Response
Thank you very much! Your guidance and comments have significantly improved our manuscript. We have carefully revised the manuscript. Here is our revised manuscript and our response to your comments. Please review it. Thank you!
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThis study employs 3DRTM to simulate the in-situ leaching (ISL) process in a mining area and provides valuable insights by comparing various pollution control strategies. This research is of significant interest as it contributes to enhancing our understanding of groundwater remediation for uranium contamination. My comments are as follows:
What are the units for these parameters in Table 1?
Lines 137-141, Only mineral dissolution or precipitation is considered in this model. Why do the authors not consider adsorption or reduction in this study?
Lines 138-141 should include the inclusion of chemical formulas for various minerals in the text, as this would enhance its readability.
What is the limitation of this reactive model or this study? This analysis can help the readers to further understand this study and widen its application to solve other similar problems.
Comments on the Quality of English LanguageThe English language can be enhanced through moderate editing.
Author Response
Thank you very much! Your guidance and comments have significantly improved our manuscript. We have carefully revised the manuscript. Here is our revised manuscript and our response to your comments. Please review it. Thank you!
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsManuscript focused on "The research on controlling groundwater pollution caused by in-situ leaching uranium: A case study in Bayan-Uul Area, Northern China" is referenced with good figures. The work is interesting and manuscript is well compiled. I will suggest authors to provide more details on hydrogeology: water level behaviour, fluctuations etc. How many groundwater structures are there in the study area(some bore holes are shown? any more structures ?) and what is the total extraction? What are the limitations of this methodology and implications of the work should be clearly shown.
Author Response
Thank you very much! Your guidance and comments have significantly improved our manuscript. We have carefully revised the manuscript. Here is our revised manuscript and our response to your comments. Please review it. Thank you!
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript has improved after revisions. All my comments were properly addressed, and I do not have further technical questions for the authors.
The quality of the presentation could be enhanced. Some plots, such as those reported in Figure 10, either report small-font texts or symbols, or present some visual problems. In figure 10, for instance, notice that labels are crossed by the vertical axis. These are minor aspects that could be easily fixed by the authors. Adjustments in the original Excel files (or other program) used to create figure 10 (as well as other figures) can easily improve the appearance of the figure.
Other than that, I can recommend accepting the manuscript.
Comments on the Quality of English Language
English may require proofreading by a native speaker, but it is acceptable in present form.
Author Response
Thank you very much for your review! Based on your comments, we have improved the manuscript. We have made further revisions to the figures. We have also revised the results and discussion sections as well as other parts of the manuscript. We have improved the language. Please see our manuscript and response. Thank you very much！
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors considered comments and improved the manuscript accordingly.
Author Response
Thank you very much for reviewing the manuscript! With your guidance, our manuscript has been greatly improved. Thank you very much！
Author Response File: 
Author Response.docx
