Optimization of the Groundwater Remediation Process Using a Coupled Genetic Algorithm-Finite Difference Method
Round 1
Reviewer 1 Report
This study presents a numerical model, verifies it with physical and analytical models, and applies the numerical model to a synthetic case study to demonstrate its power of optimizing the groundwater remediation process in terms of optimizing the location of oxidant source. Unfortunately, there are some minor flaws and a few major flaws remaining.
Minor comments:
Lines 63-73: It's good that a brief summary of GA is given, but this should be explained in the methodology and here instead the selection of GA should be justified, which is not done anywhere in the paper.
Equations in general: Please explicitly explain or define every term that appears in the equation, and please make the symbols used in the text and in the equations consistent.
Equations 6 and 7: It's not clear whether the retardation factors for the contaminant and for the oxidant are the same; if different, they should be marked.
The arbitrary location in section 4.3: This analysis presents one specific arbitrary design. It's not clear how arbitrary design is defined/generated. Is it randomly generated, or solicited from experienced engineers (without rigorous analysis), etc.
Figure 9: It's not obvious from Figs 8 and 10 why contaminant concentration would increase over time like shown in Fig 9, and it's not explained or discussed why at some locations, like Fig 9(b), the optimized design would lead to higher contaminant concentration, and what's the trade-off.
Major comments:
1: Frankly speaking, there have been many studies that developed numerical models or modules of existing models that targets complicated heterogeneous groundwater transport and remediation problems. The study did not justify the need to develop a separate model for the purpose of the study, especially when the applied case is a synthetic case. Thus, the development and the verification of the model could only be considered a must-have step in the application of the model, but not a component of the scientific innovation of this study. If there is a valid reason why a separate model is needed, it should be explicitly discussed.
2: As a continuation of the point above, the highlight of the study falls onto the application of the model to the optimization of remediation. However, this research objective is only minimally discussed in the introduction, and the synthetic case study was not explained in the methodology at all. This particular section setup leaves the audience essentially ignorant about the application case study until section 4.3. Section 4.3 also only minimally explains the synthetic case study, but did not justify the importance or significance of such a synthetic setup, or it's practical implication, etc. Figures 8 through 10 are supposed to be the main highlight of the results but are only minimally discussed.
3: Equation 8 is the application of Darcy's law to calculate specific discharge of groundwater, not the velocity. It is not clear whether a step of converting discharge to seepage velocity is omitted or the discharge is used in the ADE instead of velocity. Because it's fundamental to the physics of the model, the audience is left confused with this equation.
Author Response
First of all, we would like to thank you for your interest and high quality and constructive reviews of the of our manuscript. We agreed with all of the comments and revised
our manuscript based on these comments. Our responses are given in a point by point
manner below. The reviewers comments are in italics. Changes to the manuscript are
shown in red. To facilitate the work of the reviewers, in some instances we refer to the
manuscript indicating the line numbering.
Looking forward hearing from you soon.
Sincerely,
Univ.-Prof. Dr.-Ing. Tim Ricken
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article discusses an interesting issue in terms of both basic research and application. The authors present model studies supported by experimental verification, which is important for the value of the work. I rate the article highly and I think it is worth publishing.
However, I have serious reservations about the used notation of mathematical formulas. Authors should carefully examine the equations and try to make the notation clear and unambiguous. For this purpose, a list of all variables and parameters should be prepared and provided, along with their detailed description and dimension.
The use of the same letter, eg "k", to express different physical quantities should be avoided.
The method of indexing variables is also confusing. In many cases it is not known what is an index and what is an exponent. For example, averaged c with upper index 1 can be understood as c with an exponent (-1), etc.
In addition, you should carefully check all the equations, e.g. (19), line two: Kdc - is it capital K or small k, and is this term dimensionless like S?
Equations (10), (13): if the variable has a dimension, it cannot equal 0, but 0 [dimension]. By the way, in my opinion, the authors should limit the number of equations to the necessary minimum, containing innovative elements.
Figure 1 is somewhat not scientific. Please change to a professional figure with description and parameters. In addition, the remaining figures should be described in detail.
In the experimental part, the variables and parameters are described in words - the same markings as in the model should be used.
To sum up, authors should, based on the above guidelines, make the article more user-friendly and limit the material to the necessary, innovative scope.
After these changes, in my opinion, the article will be able to be published.
Author Response
Dear Reviewer 2,
First of all, we would like to thank you for your interest and high quality and constructive reviews of the of our manuscript. We agreed with all of the comments and revised
our manuscript based on these comments. Our responses are given in a point by point
manner below. The reviewers comments are in italics. Changes to the manuscript are
shown in red. To facilitate the work of the reviewers, in some instances we refer to the
manuscript indicating the line numbering.
Looking forward hearing from you soon.
Sincerely,
Univ.-Prof. Dr.-Ing. Tim Ricken
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors' prompt and detailed response is much appreciated, and the minor comments have all been well-addressed. However, the major concerns remain.
For major comments 1 and 2, probably those were misunderstood and probably I was not clear. Apology for that, and I'd like to reiterate and clarify the comment. The comment is not about "whether verifying the numerical model is important", on which I agree very well with the authors that it's important. Rather, the study does not justify the need to develop a separate model, given that there are other numerical models that have been verified, applied, and tested in past studies. Examples include MODFLOW, HYDRUS, HydroGeoSystem, Open GeoSystem, Parflow, etc.
Currently in the manuscript, there is no review of the other models and their verification and/or application studies, nor is there any explanation why it's needed to develop a separate model rather than just using the existing models. Therefore, 1) lack of review and 2) lack of justification, combined together, lead to a reduction of the scientific significance of the model verification in this study.
I'd like to also reiterate major comment 3 that equation 8 IS NOT for velocity. It is the calculation of specific discharge using Darcy's law, and is sometimes referred to as "Darcy velocity". Seepage velocity, on the other hand, needs to take into account the effective porosity. Please refer to section 3.1.2 (on Darcy's law) and 8.8 (on Advection Dispersion Equation) in Todd and Mays (2004).
Reference:
Todd, D. K., & Mays, L. W. (2004). Groundwater hydrology. John Wiley & Sons.Author Response
Our response to the reviewer's comments are included in the attached file.
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors took into account most of the reviewer's suggestions. I suggest the authors review the article again in terms of editing. In my opinion, after minor corrections, the article is suitable for publication.
Author Response
Our response to the reviewer's comments are included in the attached file.
Author Response File: Author Response.pdf
