From Spatial Characterisation to Prediction Maps of the Naturally Occurring Radioactivity in Groundwaters Intended for Human Consumption of Duero Basin, Castilla y León (Spain)

Round 1

Reviewer 1 Report

Check the attached file.

Comments for author File: Comments.pdf

Author Response

The authors would like to acknwoledge the assessment, as well as all the revisions and suggestions made by the reviewer in order to improve the quality and clarity of this article.
1. The authors have revised and modified Figure 1 as directed by the reviewer.
2. The authors have revised and modified Figure 2 as directed by the reviewer.
3. The authors have revised and modified Figure 3 as directed by the reviewer. Due to the modifications made according to the indications referred to in point 6, Figure 3 is Figure 4 in the revised manuscript.
4. The authors have revised and modified according to the instructions of the reviewer.
5. The authors have revised and modified according to the instructions of the reviewer.
6. The authors have revised and modified according to the reviewer's instructions, including the contents cited in the results section.
7. The authors have revised and modified the references to the corresponding figures in the manuscript in detail.
8. The authors have revised and modified the numbering of the Conclusions section.
9. In accordance with the comments and suggestions proposed by the reviewer, the authors have revised, expanded and modified the content with the aim of clarifying the explanation with arguments and bibliographical references.

Reviewer 2 Report

Dear Authors,

You have addressed a very important topic. The role of groundwater as drinking water resource will increase in the future according to the global change. Radioactivity of groundwater is a new quality parameter in the last years in drinking water regulation. Therefore, generally very few information is available about this parameter. Furthermore, the recommended screening method, the gross alpha and beta activity concentration measurements, do not provide information about the specific radionuclides, therefore interpretation/origin of the occasionally elevated values remains unknown, and rarely investigated.

You have provided a comprehensive overview about the distribution of the most common natural radioactive isotopes in the Castilla y León region, Spain. You have discussed the results regarding the geological background. I personally very welcome those results which underline that gross alpha and gross beta activity analyses have limitations and rather nuclide specific activity measurements should be used. Regarding this issue you may also look the very recent paper of Jobbágy et al. (2022) (https://doi.org/10.1016/j.apradiso.2022.110304) , which shows the results of the European wide proficiency test on gross alpha/beta activity determination.

In line 92 you have written that your study presents a holistic radioactivity assessment as you evaluate your results in the frame of the main lithologies and their permeabilities. I would argue with this statement, because to the holistic approach would belong also that you consider the organised movement of groundwater. The basin-scale groundwater flow concept helps to understand the origin and distribution of the different physicochemical characteristics and components of groundwater. Please see the work of Tóth (1999) (https://doi.org/10.1007/s100400050176). Areas of different hydraulic regimes (recharge, midline, discharge) even within the same aquifer are characterised by different geochemical environment, from oxidizing to reducing, respectively. Therefore, in case of redox-sensitive parameters, such as uranium or radium, understanding groundwater flow systems is a very important aspect. In your work this is missing, so I won’t talk about holistic approach. You should clearly state, that hydrogeological evaluation of the area and discussion of your results from this aspect are out of the scope of your study, you just deal with the geological background. Nevertheless, I strongly recommend that you consult with hydrogeologists and complement your very valuable survey with a hydrogeological discussion and publish it in a separate paper. To do that you should also provide all the basic data of the wells (including surface elevation (in m above sea level), elevation of the screening section of the well (also in m asl), etc.). Very important to measure the ph, electric conductivity, temperature, redox potential, dissolved oxygen content on the field, during sampling and provide also these data. Redox conditions are very important to interpret the measured uranium and radium values. Also the main components in groundwater show important information about the flow paths, therefore a Piper diagram or similar should be also necessary. It is clear to me, that to complement your work with all these hydrogeological evaluation would result in a huge paper, that’s why I recommend to include it in a separate one. After that you have a holistic view about your region and the origin of the natural radioisotopes in groundwater.

Your presented work is well written. I have only few specific comments. Firstly, all geographic names which are mentioned in the text should be present on a figure, that the readers can follow the locations. Another minor issue is that you should revisit the citation of the figures in the text, because sometimes you just refer as “seen in Fig”, but you do not specify on which.

Congratulation to your work and looking forward to see the hydrogeological evaluation of your results!

Author Response

Dear Reviewer,

The authors would like to acknowledge the valuable comments made by the reviewer and we would take them into account in further future work. According to the specific indications relative to minor issues, the authors have reviewed and modified the figures referring to the main geographic names mentioned in the text, as well as the incomplete references in the text to their respective figures.

Reviewer 3 Report

Please, see attached file for my comments.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

In general, the article is well written, the concept of the research conducted is good, from sampling to interpretation methods, but there is a major problem. Interpolation of (any) concentrations in groundwater can be done only within a single aquifer, i.e. within hydraulically connected aquifers. If the boundaries of the aquifer are not respected, this will lead to completely wrong conclusions. For example, if there is rock with low permeability (without groundwater) between two aquifers, it can be concluded from this approach (and the maps shown) that there is groundwater with a certain radioactivity in this low permeable material, which is completely wrong. It is neither an aquifer, nor does it contain groundwater.

Therefore, a detailed hydrogeological description of the area with defined boundaries of the individual aquifers and their mutual relationships is required. Accordingly, it must also be shown how many sampling points are present in which aquifer. Subsequently, the areas in which interpolation is possible (aquifer or several hydraulically interconnected aquifers) must be determined, and the interpolation must be performed separately for each area.

Author Response

Dear Reviewer,

The authors would like to acknowledge your valuable comments.  We agree with your indications, that we have followed and performed entirely, respecting the hydraulic boundaries of the hydrogeographical units,  characterising the three main aquifer types and analysing separately aquifers hydraulically connected as well as the limited and confined aquifers. Accordingly, we have generated new figures.

Round 2

Reviewer 1 Report

I would like to accept the fully revision of the manuscript ’’Spatial distribution of naturally occurring radioactivity in groundwaters intended for human consumption of Castilla y León (Spain)’’ for publication in agronomy journal.

Author Response

The authors would like to express our profound gratitude to the reviewer for the acceptance of our research paper. 

Reviewer 4 Report

The interpolation was done in the same way as in the previous version. The difference is that now these polygons are only cut graphically according to the boundaries of the aquifer. This means that there is no difference from the previous version. However, this is not the point. The interpolation may only be done within the boundaries of the individual aquifer, i.e. for hydraulically connected aquifers. In this case, for example, separately for hydrogeologic unit 20, separately for 21, and all others together only if they are hydraulically connected.

There is a possibility that all of this has been done, but if so, it should be clearly written and the possibility of control should be given. It is not apparent what the minimum, maximum, etc. values are within an individual aquifer, and there is no way to control the end result.

Author Response

The authors would like to acknowledge your suggestions. In agreement with your indications,  we have interpolated respecting the hydraulically interconnected aquifers. We have limited the scope of this paper research considering only the groundwater samples gathered within the region limits where interpolation can be done. The hydrogeological units 20 and 21 are not included in this work due to both comprised confined aquifers. Furthermore, with the aim of clarifying the results shown in the manuscript, we have included a table (Table 3) in which are reported the minimum, maximum and median values for the samples considered in the IDW method.