Review Reports - Factors Controlling the Spatial and Temporal Variability in Groundwater <sup>222</sup>Rn and U Levels

Round 1

Reviewer 1 Report

General Comments:

This study focuses on the distribution of uranium and radon concentrations of groundwater including other geochemical parameters. The objectives of this study are to investigate the quantity and spatial distributions of radon and uranium, and to determine the factors controlling these radioactive chemicals. However, this manuscript needs to be further revised as mentioned in the section below.

Manuscript Comments:

-Lines 19-21: "Large variations were observed in groundwater, concentrations of ²²²Rn and ²³⁸U, ranging between 0.6±0.1–674.7±8.7 Bq L^-1 and 0.1–117.0 µg L^-1, respectively." Based on Table A1, the concentrations of ²²²Rn and ²³⁸U should range between 0.6±0.1–673.7±8.7 Bq L^-1 and 0.0–117.0 µg L^-1, respectively. Please re-check and also consider modifying in Lines 138-139.

-Lines 43-44: "Furthermore, ²²²Rn in groundwater and soil air has been monitored worldwide to predict earthquakes and to understand natural processes [11-13]." ²²²Rn in groundwater and soil air or in groundwater, soil, and air? Please check if your intended sentence is correct.

-Lines 83-84: "Samples were taken after the wells were purged of their total volume at least three times or over 15 min using a submersible pump installed in the wells to remove well bore storage." Their total volume refers to the entire volume of groundwater in the well? The well depths varied from 25-200 m. How about the diameter sizes of the wells? It sounds tough to purge their total volume three times even with more than 15 min, especially for the well of large depth (e.g., 200 m depth). Please confirm if this description is correct.

-Lines 89-90: In the legend of Figure 1, it looks better if you change "Sampling site" to "Sampling point", where the caption of Figure 1 should be shortened as "A simplified geological map of the sampling site in Yongin area, Korea".

-Lines 93-94: "A total of 8 ml of each sample were injected and mixed with a previously prepared 12 mL of the liquid scintillator cocktail solutions (Optiphase Hisafe3)." I think it is better if you remove a previously prepared and then mention the specific chemical name to form that liquid scintillation cocktail solution.

-Lines 127-128: "Groundwater sample for ²³⁸U analysis was immediately filtered through 0.45 µm cellulose membrane, and then acidified with nitric acid and stored in pre-cleaned vails." If you specify the amount of nitric acid to be added (or the specific pH value after adding nitric acid), it becomes more informative. One more thing, pre-clean vails or pre-cleaned vials? Please confirm whether which one is correct. Also, you mentioned ²³⁸U concentration was measured by ICP-MS, but I wonder whether ICP-MS analyzes only ²³⁸U concentration or the total uranium concentration (i.e., concentration of ²³⁸U including the uranium with different isotopes).

-Lines 140-141: "The highest concentrations of ²²²Rn and ²³⁸U were observed at YI21 and YI31, respectively." Based on Table A1, it should be at YI21 and YI32. Please check it again.

-Lines 152-155: You describe the correlation, but some parts of it you did not include correlation coefficient r. I think it is better to include it as the statistical evidence even though there is no or extremely weak correlation. Also, refer to lines 204-209.

-Line 200: Figure 5 shows the legends with the number from 0-700 (in Fig. 5a) and 0-120 (in Fig. 5b), but it seems no information or explanation about that. Please at least add the explanation in the figure or its caption to make it more understandable.

-Line 215: "...deep wells and showed a significnat positive correlation..." Wrong spelling for significnat. Please revise it to significant.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 1 Comments

[General Comments]

Point 1: This study focuses on the distribution of uranium and radon concentrations of groundwater including other geochemical parameters. The objectives of this study are to investigate the quantity and spatial distributions of radon and uranium, and to determine the factors controlling these radioactive chemicals. However, this manuscript needs to be further revised as mentioned in the section below.

Response 1: Thank you for comments. We carefully considered all comments from the reviewer#1 in the revised version.

[Manuscript Comments]

Point 2: Lines 19-21: "Large variations were observed in groundwater, concentrations of ²²²Rn and ²³⁸U, ranging between 0.6±0.1–674.7±8.7 Bq L^-1 and 0.1–117.0 µg L^-1, respectively." Based on Table A1, the concentrations of ²²²Rn and ²³⁸U should range between 0.6±0.1–673.7±8.7 Bq L^-1 and 0.0–117.0 µg L^-1, respectively. Please re-check and also consider modifying in Lines 138-139.

Response 2: Thank you for correction. We did some mistakes in Table A1, Lines 19-21, and Lines 138-139. We revised the lowest uranium concentration (YI52) from “0.0 µg L^-1” to “0.02 µg L^-1”in Table A1, and changed “674.7±8.7 Bq L^-1” to “673.7±8.7 Bq L^-1” in the revised manuscript as suggested by the reviewer#1 (Line 22 and Line 143).

Point 3: Lines 43-44: "Furthermore, ²²²Rn in groundwater and soil air has been monitored worldwide to predict earthquakes and to understand natural processes [11-13]." ²²²Rn in groundwater and soil air or in groundwater, soil, and air? Please check if your intended sentence is correct.

Response 3: We changed this sentence to “Furthermore, ²²²Rn in groundwater has been monitored worldwide to predict earthquakes and understand natural processes [11-13]." (Lines 45-46).

Point 4: Lines 83-84: "Samples were taken after the wells were purged of their total volume at least three times or over 15 min using a submersible pump installed in the wells to remove well bore storage." Their total volume refers to the entire volume of groundwater in the well? The well depths varied from 25-200 m. How about the diameter sizes of the wells? It sounds tough to purge their total volume three times even with more than 15 min, especially for the well of large depth (e.g., 200 m depth). Please confirm if this description is correct.

Response 4: Yes, it is difficult to purge the total volume of the wells with large depth for several minutes although the sampled wells were NX-borehole (76 mm diameter) as mentioned by the reviewer#1. However, we tried to replace their volumes more than 15 min purging. Therefore, we changed this sentence to “Samples were taken after the wells were purged by pumping for more than 15 min using a submersible pump to remove well bore storage." in the revised version (Lines 85-86).

Point 5: Lines 89-90: In the legend of Figure 1, it looks better if you change "Sampling site" to "Sampling point", where the caption of Figure 1 should be shortened as "A simplified geological map of the sampling site in Yongin area, Korea".

Response 5: We changed "sampling site" to "sampling point" in the entire manuscript. The caption of Figure 1 was shortened as "A simplified geological map of the sampling site in Yongin area, Korea" in the revised version as suggested (Line 91).

Point 6: Lines 93-94: "A total of 8 ml of each sample were injected and mixed with a previously prepared 12 mL of the liquid scintillator cocktail solutions (Optiphase Hisafe3)." I think it is better if you remove a previously prepared and then mention the specific chemical name to form that liquid scintillation cocktail solution.

Response 6: We changed this sentence to “A total of 8 ml of each sample were injected and mixed with 12 mL of a commercial liquid scintillator cocktail solution (Optiphase Hisafe3, PerkinElmer).” in the revised version as suggested (Lines 93-95).

Point 7: Lines 127-128: "Groundwater sample for ²³⁸U analysis was immediately filtered through 0.45 µm cellulose membrane, and then acidified with nitric acid and stored in pre-cleaned vails." If you specify the amount of nitric acid to be added (or the specific pH value after adding nitric acid), it becomes more informative. One more thing, pre-clean vails or pre-cleaned vials? Please confirm whether which one is correct. Also, you mentioned ²³⁸U concentration was measured by ICP-MS, but I wonder whether ICP-MS analyzes only ²³⁸U concentration or the total uranium concentration (i.e., concentration of ²³⁸U including the uranium with different isotopes).

Response 7: We changed this sentence to “Groundwater sample for U analysis was immediately filtered through 0.45 µm cellulose membrane, and then acidified to ~pH 2 with nitric acid and stored in the vails which were pre-cleaned with nitric acid and de-ionized water.” in the revised version (Lines 127-129). The uranium concentration measured in this study is the total uranium concentration as mentioned by the reviewer#1 and thus, we changed ‘²³⁸U’ to ‘U’ in the entire manuscript. Thank you for correction!

Point 8: Lines 140-141: "The highest concentrations of ²²²Rn and ²³⁸U were observed at YI21 and YI31, respectively." Based on Table A1, it should be at YI21 and YI32. Please check it again.

Response 8: Thank you for correction. We changed “YI31” to “YI32” in the revised version (Line 144).

Point 9: Lines 152-155: You describe the correlation, but some parts of it you did not include correlation coefficient r. I think it is better to include it as the statistical evidence even though there is no or extremely weak correlation. Also, refer to lines 204-209.

Response 9: We included the correlation coefficients in Figure 3 and 4. Also, we referred them in the revised version (Line 155-159 and Lines 211-215).

Point 10: Line 200: Figure 5 shows the legends with the number from 0-700 (in Fig. 5a) and 0-120 (in Fig. 5b), but it seems no information or explanation about that. Please at least add the explanation in the figure or its caption to make it more understandable.

Response 10: Figure 5a and 5b showed the concentrations of ²²²Rn and U, respectively. Therefore, we used the different concentration scales considering their concentration ranges (0-700 Bq L^-1 for ²²²Rn and 0-120 µg L^-1 for U). We added the explanation in the caption of Figure 5 (Lines 207-208).

Point 11: Line 215: "...deep wells and showed a significnat positive correlation..." Wrong spelling for significnat. Please revise it to significant.

Response 11: Thank you for correction. We changed as suggested (Line 221).

[End]

Author Response File: Author Response.docx

Reviewer 2 Report

Please use more relevant keywords.

There is an important gap in method: how do you analyze the data: spatial and temporal variations?

I strongly recommend presenting the result and discussion section together.

Figures 3 and 4: please rescale you data and re-analyze.

Effect of lithology and fault: from figure 1, it is clear that the number of samples in two main geology strata is not the same. Therefore, please clarify which method did you apply for analysis? for comparing mean?

Line 176: use another sub-section. E.g. spatial …

Please add information about how did you do the spatial analysis? Software? Techniques?

Figures 6: please rescale your data and re-analyze.

Author Response

Response to Reviewer 2 Comments

Thank you for comments. We carefully considered all comments from the reviewer#2 in the revised version.

Point 1: Please use more relevant keywords.

Response 1: Thank you for comments. As suggested by the reviewer#2, we changed the keywords which are more relevant (Line 31).

Point 2: There is an important gap in method: how do you analyze the data: spatial and temporal variations?

Response 2: The spatial variations of the observed ²²²Rn and U concentrations obtained from 98 groundwater wells located in two different geological characteristics (granite or gneiss area, Figure 5) were analysed using Grapher (Golden Software Inc., version 12). The ²²²Rn concentration in the shallow groundwater wells (<30 m, five wells) obtained in August, October, and November and precipitation data were plotted together using Sigmaplot (Systat Software, version 13) in Figure 7 to determine the potential reasons for the temporal variations of ²²²Rn concentration.

Point 3: I strongly recommend presenting the result and discussion section together.

Response 3: changed as suggested (Line 135).

Point 4: Figures 3 and 4: please rescale you data and re-analyze.

Response 4: We re-analysed the data and included additionally the correlation coefficients in Figure 3 and 4 as suggested.

Point 5: Effect of lithology and fault: from figure 1, it is clear that the number of samples in two main geology strata is not the same. Therefore, please clarify which method did you apply for analysis? for comparing mean?

Response 5: Yes, the number of samples in two geology strata is not same. However, we tried to collect groundwater samples in the study area as many as possible and we compared the means of ²²²Rn and U concentrations in two geology strata.

Point 6: Line 176: use another sub-section. E.g. spatial …

Response 6: changed as suggested.

Point 7: Please add information about how did you do the spatial analysis? Software? Techniques?

Response 7: We used Grapher (Golden Software Inc., version 12) for analyse the spatial analysis. We added this information in the revised manuscript (Lines 131-133).

Point 8: Figures 6: please rescale your data and re-analyze.

Response 8: We rescaled and re-analysed the data of ²²²Rn and U concentrations and the correlation coefficient was added in Figure 6 in the revised version as suggested.

[End]

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The revised manuscript looks significantly improved and seems qualified enough to accept in the present.