Groundwater Risk Assessment Based on DRASTIC and Special Vulnerability of Solidified/Stabilized Heavy-Metal-Contaminated Sites
Round 1
Reviewer 1 Report
Interestingly, you try to assess the risk of groundwater contamination of solidification/stabilization heavy metal contaminated sites. Can you give the information on how much data you collected before to provide the risk system index in Table 2-Table 9?
Abstract; You should add the AHP result that you mentioned in the manuscript.
Line 53; Give more information about the stimulating period of 52-104; what’s the number represented?
Line 74; please define the full name of DRASTIC and every abbreviate word that you mentioned the first time.
Line 124; please edit the word “side protection.” It showed double writing.
Line 324; In the sentence “The number of freeze-thaw cycles was small”; you referred to the same number of less than 30 or another number; please define it.
Line 410-413; How to relate the average percentage of site inherent vulnerability score, the weight of the site’s intrinsic vulnerability with Figure 3.
Groundwater risk assessment under scenarios 1 and 2 were investigated and filled the data from the previous Tables as you mentioned in Table 10; however, can you explain in detail, how to get the number in The Rating?
Author Response
Response to Reviewer 1
Thanks for your careful comments and suggestions. Those comments are all valuable and very helpful for revising and improving our manuscript and significantly guiding our research. The reviewer comments are in italic font below, and specific concerns have been numbered. Our response is given in normal font, and changes/additions to the manuscript are given in blue text.
Comment 1: Can you give the information on how much data you collected before to provide the risk system index in Table 2-Table 9?
Response 1: Thanks very much for your comments.
Before establishing the groundwater pollution risk assessment index system, we reviewed a large amount of relevant literature and also collected some relevant data. The following are the details of the work.
(1) By reviewing the literature related to groundwater risk assessment, we identified the commonly used Analytic Hierarchy Process to establish the risk assessment framework and then reviewed the literature on numerical simulation of groundwater in the unsaturated zone to study the process of contaminant release to contaminated groundwater, combined with actual remediation cases, and finally determined the conceptual model for risk assessment.
(2) In this paper, a total of 18 evaluation indicators were selected, but there are more than 18 factors affecting groundwater risk at S/S sites in actual sites, such as oxidation-reduction potential, temperature, type of S/S remediation chemicals, iron and manganese oxide content, etc. However, the evaluation system cannot contain all indicators, so we summarized the findings inside a large amount of literature on S/S remediation of heavy metal soils. The literature types include S/S remediation agents, adsorption and desorption rules of S/S remediation soils, acid rain leaching of S/S remediation soils and accelerated experiments, actual remediation cases, and other literature, summarizing the influence mechanism and importance of each evaluation index, and combining the principles of scientificity, importance, operability, and convenience, we screened 18 evaluation indexes in Table 2.
(3) The next step is the quantitative issue involving the grading and scoring of indicators.
In establishing the contents in Table 3, we referred to some landfill groundwater risk assessment literature and also
collected some data. The site size grading and scoring are combined with the landfill grading data, as well as the data of 76 contaminated sites in China and 329 sites in France, and the rest of the indicators refer to landfills.
The contents in Table 4 are the key part closely related to S/S. We reviewed the literature related to heavy metals in S/S remediation soils, summarized the general value range and distribution law of these six indicators in the literature, and combined them with the actual consideration of S/S sites.
In establishing the contents in Table 5, we reviewed the DRASTIC-related literature. Since DRASTIC is already mature and has been applied relatively well, we deleted the soil media indexes after combining the model's characteristics in this paper, and the other parameters remained unchanged.
In establishing Table 6, we reviewed China's ecological environment quality reports in recent years to determine the grading and scoring of acid rain indicators, and the number of freeze-thaw cycle indicators was determined by reviewing the relevant literature summary.
Table 7 shows the calculation basis of the Analytic Hierarchy Process method, and Table 8 was determined by combining the literature summary and expert opinions.
Table 9 reviewed the grading methods commonly used in the risk assessment literature, and the grading method applicable to the model of this paper was selected.
Comment 2: Abstract; You should add the AHP result that you mentioned in the manuscript.
Response 2: Thank you very much for your suggestions. We added the AHP conclusion in the abstract section.
Page 2, Line 34-40: Each evaluation index was graded and assigned a scoring value, combined with Analytic Hierarchy Process(AHP) to calculate index weights. The comprehensive weights of site hazard, contaminant stability, aquifer vulnerability, and natural conditions are 0.1894, 0.3508, 0.3508, and 0.1090, respectively. The isometric method was used to classify the pollution risk into five risk levels(very low risk [0, 2), low risk [2, 4), medium risk [4, 6), high risk [6, 8), and very high risk [8, 10] ), and a groundwater comprehensive index pollution risk assessment model was established.
Comment 3: Line 53; Give more information about the stimulating period of 52-104; what’s the number represented?
Response 3: Thank you very much for your suggestions. We have added that section.
Page 4, Line 84-86: Zhengtao Shen used the accelerated aging method and found that the stabilization effect decreased when the TCLP leaching concentration of Pb and Cd increased over a simulated acid rain period of 52 to 104 years.
Comment 4:Line 74; please define the full name of DRASTIC and every abbreviate word that you mentioned the first time.
Response 4: Thank you very much for your suggestions. I have added that section.
Page 6, Line 110-115: DRASTIC is the most commonly used model for evaluating the inherent vulnerability of aquifers based on a weighted combination of seven hydrogeological settings(depth to water table, net recharge of aquifer, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity). DRASTIC was named by the abbreviation of each index, an empirical model developed by USEPA for assessing groundwater contamination potential.
Comment 5: Line 124; please edit the word “side protection.” It showed double writing.
Response 5: We feel sorry for our carelessness. The correction is revised. Thanks for your correction.
Page 8, Line 164-165: Therefore, four evaluation indexes were selected: site size, top protection, side protection, and bottom protection.
Comment 6: Line 324; In the sentence “The number of freeze-thaw cycles was small,”; you referred to the same number of less than 30 or another number; please define it.
Response 6: Thank you very much for your suggestions. We have added that section.
Page 19, Line 395-397: Since the effect on S/S heavy metals was not obvious at a lower number of freeze-thaw cycles (compared with 30)[55], the 1st level was set to 5 times, and the maximum level was set to 50 times.
Comment 7: Line 410-413; How to relate the average percentage of site inherent vulnerability score, the weight of the site’s intrinsic vulnerability with Figure 3.
Response 7: Thank you very much for your comments. We have added that section.
Page 20, Line 421-424:The comprehensive weights of site hazard, contaminant stability, aquifer vulnerability, and natural conditions are 0.1894, 0.3508, 0.3508, and 0.1090, respectively, which also represented the weighting of the 4 influencing factors on the groundwater pollution risk assessment of 18.94%, 35.08%, 35.08% 10.90%, respectively.
Page 24-25, Line 512-514: We calculate the sum of the scores of aquifer vulnerability as a percentage of the total score of all evaluation indicators in each scenario and then find the arithmetic mean.
Comment 8: Groundwater risk assessment under scenarios 1 and 2 were investigated and filled the data from the previous Tables as you mentioned in Table 10; however, can you explain in detail, how to get the number in The Rating?
Response 8: Thank you very much for your comments. Please let me explain the exact steps. We take the site size data of As in scenario 1 as an example; the site size of As is 119439m3, and the index belongs to the Site Hazard impact factor; we check Table 3, and we can see that 119439 belongs to Level 4 (5×104 ~20×104), Level 4 assigns a score of 7, and then we check Table 2 to get Site Size C11 comprehensive weight of 0.0972, the two multiplied equal to 7 × 0.0972 = 0.68, so from Table 10 we can view the value of 0.68, the rest from The indicator takes similar values. We have also added the corresponding content to the manuscript.
Page 24, Line 494-502:Further analysis of the differences in the evaluation indexes of the indicator layer showed that Cd and As had different scores in the leachable form ratio and soil pH, with 0.67 and 0.40 for the leachable form ratio and 0.08 and 0.31 for the soil pH, respectively. 12.5% of the Cd leachable form ratio was greater than 9.05% of the As, resulting in the index levels of level 3 and level 2 for the leachable form ratio of Cd and As, respectively (Table 4) and assigning scores of 5 and 3, respectively, with greater risk for Cd. There have been many studies showing that Cd in soil heavy metals belong to high activity and easy release[51,57,58], and further research is needed to reduce the leachable form ratio of Cd.
Page 24, Line 503-511:Although the soil pH was 9.05, Cd and As had different properties for pH changes due to their cationic and anionic group heavy metals, respectively. In the soil pH index, Cd and As were graded as level 2 and level 3 and assigned different scores of 1 and 4, respectively (Table 4), with As being more risky. The different scores assigned to the two heavy metals multiplied by the evaluation index weights result in different scoring values. Therefore, for compound heavy metal contaminated sites, the effect of soil pH change on different heavy metal ions needs to be considered comprehensively, and soil pH control near 7.5 may be less risky for different heavy metals (Table 4) [45-46,52-53].
Reviewer 2 Report
I read carefully the manuscript titled " Groundwater risk assessment based on DRASTIC and special vulnerability of solidification/stabilization heavy metal contaminated sites". The subject of the manuscript is very interesting and relevant. The structure is adequate.
Specific comments to the author(s):
· Quantitative results should be provided in the abstract to make it more comprehensive. The results of the study should be added in the abstract section.
· More literature review about the other methods is needed, hence manuscript could be substantially improved.
· There are mixing between methods and results in the context.
· Methodology, results, and discussion should be separated into sections.
· Perform a last check in the English language. Some phrases would be improved.
· The results and discussion section in the present form is relatively weak and should be strengthened with more details and justifications.
· Re-write the conclusion to be more informative.
· Please follow the journal guidelines and formatting.
Overall, this work could be accepted for publication after addressing the above issues.
Author Response
Response to Reviewer 2
Thanks for your careful comments and suggestions. Those comments are all valuable and very helpful for revising and improving our manuscript and significantly guiding our research. The reviewer comments are in italic font below, and specific concerns have been numbered. Our response is given in normal font, and changes/additions to the manuscript are given in blue text.
Comment 1: Quantitative results should be provided in the abstract to make it more comprehensive. The results of the study should be added in the abstract section.
Response 1: Thank you very much for your suggestions. We have added quantitative data and conclusions to the abstract.
Page 2, Line 23-57.
Comment 2: More literature review about the other methods is needed, hence manuscript could be substantially improved.
Response 2: Thank you very much for your suggestions. We have enriched this section in the manuscript.
Page 4, Line 81-84: For example, Fusheng Zha simulated 3 years of acid rain on cement-alkali slag cured/stabilized Zn-contaminated soil by soil column leaching experiments and found that the Zn concentration in the filtrate always met the requirements (<1 mg/L) [9].
Page 4-5, Line 86-89: Tasuma Suzuki found that curing Pb-contaminated soil with magnesium oxide was still effective after 100 years of simulated acid rain by using the accelerated aging method(Pb < 0.01 mg/L) [60].
Page 6, Line 122-125: Xiaoning Zhao constructed a groundwater pollution risk evaluation system combining groundwater vulnerability and pollution load based on simulated pollutant migration values and DRASTIC[61].
Comment 3: There are mixing between methods and results in the context.
Response 3: Thank you very much for your suggestions. We have modified these in the manuscript by dividing the methods and results into separate sections.
Comment 4: Methodology, results, and discussion should be separated into sections.
Response 4: Thank you very much for your suggestions. We have divided the Methods, Results, and discussion, Conclusion
into different sections.
Comment 5: Perform a last check in the English language. Some phrases would be improved.
Response 5: Thank you very much for your suggestions. We would polish our article.
Comment 6: The results and discussion section in the present form is relatively weak and should be strengthened with more details and justifications.
Response 6: Thank you very much for your suggestions. After we have divided Methods, Results, and discussion, Conclusion into different sections, We have added more data analysis and evidence in the results and discussion section; for example, we have added a discussion of the results of AHP to analyze the meaning of indicator weights; we have added a discussion of the case results, added an analysis of the reasons for data discrepancies, and added an analysis of the impact of key indicators on groundwater risk assessment.
Comment 7: Re-write the conclusion to be more informative.
Response 7: Thank you very much for your suggestions. We enrich this section, as detailed in the manuscript.
Comment 8: Please follow the journal guidelines and formatting.
Response 8: Thank you very much for your suggestions. We have revised the manuscript sections and related content.
Thank you for your constructive comments!
Round 2
Reviewer 1 Report
The quality of the original is good; I recommend accepting this manuscript.
Reviewer 2 Report
Dears
You can cite the following related to your subject.
https://doi.org/10.1016/j.jafrearsci.2019.103709
https://doi.org/10.1016/j.jafrearsci.2019.103709
Regards
