The Spontaneous Potential Log as an Aid in Establishing Electrical–Hydraulic Conductivity Relations in Complex Sedimentary Rock Environments: A Case Study in Taiwan

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The manuscript requires thorough proofreading for English grammar and syntax. “The results for the spontaneous potential log was then employed”-->The spontaneous potential (SP) log was then employed.  “has been seeking to not only benefit engineering practice…” should be rewritten.
2. There is excessive use of the passive voice. Please rewrite key findings in active voice to make the claims more direct and impactful.
3. The Abstract is too lengthy and includes methodological details that should be confined to the main body of the paper.
4. Figure captions must be self-explanatory; they currently lack sufficient detail to be understood without reading the main text.
5. The procedure for the proposed two-stage screening method is insufficiently detailed in the Methods section. A clear, step-by-step protocol or flowchart is required.
6. The distinction between the SP log and SPR log measurements is not consistently clear. Please clarify the precise physical property each tool provides.
7. Define what constitutes a "noise-affected sample" in the context of the logging data, as the current term is too vague for a technical method.
8. Equation 1: 05 should be change to 0.5.
9. The justification for statistical thresholds (e.g., sample size ≥ 10 for grouping) is not explained and appears arbitrary.
10. Figures require clearer axis labels, units, and improved readability (e.g., Figures 2 & 3 lack sufficient explanation).
11. Table formatting is inconsistent and some headers and abbreviations lack definitions, making interpretation difficult (e.g., Table 4 & 5).
12. Reference formatting is inconsistent; ensure journal style compliance (capitalization, punctuation, spacing).

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

water-3942009-review

The spontaneous potential log as an aid in establishing electrical-hydraulic conductivity relations in complex sedimentary rock environments: A case study in Taiwan

The present investigation highlights the feasibility of utilizing borehole geophysical logging, with particular emphasis on spontaneous potential (SP) and single-point resistance (SPR) measurements, for estimating hydraulic conductivity in geologically complex sedimentary rock environments of Taiwan’s mountainous regions. This is an interesting and highly engineering practical work. Some suggestions and opinions for modification are as follows:

1. The reliability of the two hydraulic conductivity prediction models established in the paper, especially model S2, is worrying. Model S2 is constructed based on only 6 samples, and although its coefficient of determination (R ²) is as high as 0.9456, such a small sample size can easily lead to overfitting of the model, that is, the model overly relies on specific noise in the training data rather than universal rules, thereby seriously weakening its generalization ability in extrapolation applications.
2. For Figure 3, which displays the distribution of SP values in sandstone and shale, the main text only indicates their distribution range without delving into their geological significance (such as why some sandstones have higher SP values than shale).
3. Line 394~401 attributes ∆SP<5 mV to the influence of drilling additives, but this is more like a reasonable explanation after the fact rather than a screening criterion established based on theory or experiment beforehand. Readers cannot confirm whether this threshold is applicable to other study areas.
4. The theoretical model of this study has potential, but its practicality and reliability in practical engineering projects must be demonstrated through supplementary engineering workflows, independent data validation, and interpretation linked to engineering decisions. Suggest major revisions, with a focus on enhancing the operability and predictive ability of the methods.
5. There are many problems with language expression, chart integration, and formatting standards in documents, which affect the fluency and academic professionalism of reading.

Comments on the Quality of English Language

There are many problems with language expression, chart integration, and formatting standards in documents, which affect the fluency and academic professionalism of reading.

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Lines 11-12: Include in the abstract, witch equipment was used to measure the SP and SPR?

Lines 18-20: Clearly mention the predicted parameters and prediction performance of regression model,  

Line 23: Cost effective, How?

Line 36: include comparative analysis of all methods based on their accuracy, reliability, and generalization capability to establish the correlation between spontaneous potential (SP), single-point resistance (SPR), hydraulic conductivity

Line 69: Provide reference

Include the flow chart for the methodology used,

At line 117, ultimately, only 42 out of 88 boreholes were utilized in this study, whereas in Table 2 no. of sample 87, 27, 114

Lines 112-114: Include detail of “In-situ hydrogeological tests, including fluid conductivity logging, electrical well logging, groundwater velocity measurement, temperature profiling, borehole imaging, pumping tests, and double-packer hydraulic testing. In methodology, it is not clear, also provide the summary of the data collected

Table 1: not in text

Lines 132-134: Write the names of geophysical parameters included in the analysis

Lines 211-212: Include, conceptual diagram, to send the SP signals to avoid the subjectivity of geological interpretation in defining the dominant lithology of each test interval

Results and discussion: Supports the findings the previous literature

Lines 310-347: Need focus on detailed analysis of the main findings rather than emphasizing methodology   

Line 323-324: “Correlations between SP and K were consistently very weak across all sedimentary rock samples and lithologic groups, indicating limited potential as a predictive factor”. Discuss the weak correlation technically

Conclusion needs to be strengthened by incorporating the data-based evidence    

Author Response

Please see the attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have comprehensively addressed all comments and concerns raised in the initial round of review. The revisions made to the manuscript are thorough, and the authors have provided clear, detailed, and well-structured responses to each point raised. The scientific quality, clarity, and presentation of the manuscript have been significantly improved as a result of these revisions. I believe the paper is now suitable for publication in its current form. I recommend acceptance without further revision.

Author Response

The authors appreciate the reviewer’s insightful comments and the acceptance of this manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

The authors appreciate the reviewer’s insightful comments and the acceptance of this manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have addressed all the concerns highlighted, some minor concerns are given below 

Line 320-321: Figure 2a and Figure 2b? check and correct

Strength the discussion section by including references that support the study's finding. 

Table 1 not in the text, check

Author Response

The authors have prepared a detailed point-by-point response to the reviewers' comments in the following text. We also provide a revised manuscript with all changes marked clearly in blue.

Comment 1: Line 320-321: Figure 2a and Figure 2b? check and correct

Response 1: Please see L320-321. This typo has been revised (Figure 3a and Figure 3b).

Comment 2: Strength the discussion section by including references that support the study's finding. 

Response 2: Please see L544-591. Thank you for this constructive comment. The Discussion section has been strengthened by adding targeted references that directly support the key findings of this study.

Comment 3 Table 1 not in the text, check

Response 3:  Please see L311-312. Table 1 has been included in the text. "Table 1" summarizes the patterns of abnormal signal values, which include negative values, zeros, −9999, −999, 1200, and values far outside the expected signal range. Ultimately, 10 abnormal samples (approximately 8% of the dataset) were excluded.