Review Reports - Environmental Impact Assessment of Urban Underground Pipeline Projects Based on LCA

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors The authors established a lifecycle environmental impact assessment model for urban underground pipeline projects based on LCA, defines five lifecycle stages, constructs an inventory database, selects seven environmental impact indicators, and verifies the model through a case study to propose stage-specific improvement measures. Here are the comments: 1. The abstract lacks specific quantitative results of the case study. 2. The research framework diagram (Figure 2) and lifecycle scope diagram (Figure 3) lack detailed caption explanations, and the logical connection between each module in the framework is not clearly described in the text, reducing the readability of the graphical content. 3. The basic assumptions in the 3.1 section are too rough; it only assumes constant annual energy consumption during operation and uses industry average data for missing data, but does not explain the error impact of these assumptions on the assessment results. 4. The lifecycle inventory database only covers key materials (cement, steel, concrete) and energy sources, ignoring the environmental impact of auxiliary materials (such as pipeline insulation materials, anti-corrosion coatings) commonly used in underground pipeline projects. 5. The weight determination adopts the target-distance method, but the source and calculation basis of the baseline emission level Bi and target emission level Ti in Table 12 are not explained in the text, and the rationality of the weight setting cannot be verified. 6. The case study only selects a single integrated pipe gallery project, lacking comparative analysis with ordinary underground pipelines (water supply, drainage, gas pipelines) of different types and scales, and the universality of the model is insufficiently verified.

Author Response

The authors established a lifecycle environmental impact assessment model for urban underground pipeline projects based on LCA, defines five lifecycle stages, constructs an inventory database, selects seven environmental impact indicators, and verifies the model through a case study to propose stage-specific improvement measures. Here are the comments:

The abstract lacks specific quantitative results of the case study.

Thank you for your comment. The abstract is modified to show the quotative results on the lines 27-32 in blue.
The results indicate that the photochemical ozone creation potential (POCP), atmospheric particulate matters potential (APMP), and solid waste potential (SWP) have the most significant environmental impacts, and the total environmental impact values are 70, 104 and 83.9 capita equivalent, respectively. Moreover, the raw material production and processing, operation and maintenance, and construction stages are identified as the primary contributors to these environmental impacts, and the values are 17.5, 10.6 and 1.8 capita equivalent, respectively.

The research framework diagram (Figure 2) and lifecycle scope diagram (Figure 3) lack detailed caption explanations, and the logical connection between each module in the framework is not clearly described in the text, reducing the readability of the graphical content.

Thank you for your comment. Both Figure 2 and Figure 3 are introduced to explain the structure of the frameworks on the lines 139-141, 146-151, and 184-198 in blue.
Figure 2 is based on ISO, and the evaluation system comprising four standard steps: goal and scope definition, lifecycle inventory analysis, lifecycle impact assessment, and lifecycle interpretation. Then, the assessment reports are used to show the results and problems and propose improvement measures. The reports can be used in different fields such as product development and improvement, strategy, public policies, etc.
The whole process in Figure 3 is based on the LCA framework o Figure 2. Then, a case study is used to verify the feasibility of the model. Based on the LCA theory framework, the framework for environmental impact assessment of urban underground pipeline projects is shown in Figure 2. The evaluation process consists of 4 steps, and there are more processes in each step. Firstly, the scope of the evaluation is defined, and the system boundaries are clearly established. The whole scope is the lifecycle process of urban underground pipeline projects including raw mate-rial production and processing, raw material transportation, construction, operation and maintenance, and disposal. Secondly, a lifecycle inventory analysis is conducted to systematically identify the sources of environmental impacts across all lifecycle stages to quantify their pollution emission data, according to the consumption in each stage. On this basis, using methods such as environmental impact categorization, characterization analysis, data standardization, and weighted assessment, the inventory data are trans-formed into comparable environmental impact indicator values. Finally, a case is studied to validate the assessment model, and based on the quantified results, a comprehensive analysis is performed, and targeted recommendations for environmental improvement are provided.

The basic assumptions in the 3.1 section are too rough; it only assumes constant annual energy consumption during operation and uses industry average data for missing data, but does not explain the error impact of these assumptions on the assessment results.

Thank you for your comment. We are sorry that we did not clearly introduce the assumptions. The assumptions are improved and the explanations are added on the lines 233-237 in blue.
Considering the data limitation, we also explain the limitations and will improve the database in the future, which is explained on the lines 809-815 in blue.

The lifecycle inventory database only covers key materials (cement, steel, concrete) and energy sources, ignoring the environmental impact of auxiliary materials (such as pipeline insulation materials, anti-corrosion coatings) commonly used in underground pipeline projects.

Thank you for your comment. We analyzed the impacts of some auxiliary materials based on the literature and found that compared to the key materials, the environmental impacts are much smaller. Furthermore, due to the inadequate data of auxiliary materials, the paper focuses on the key materials. In the future, we will improve the inventory database to consider more materials. The explanation is shown on the lines 329-333 in blue.

The weight determination adopts the target-distance method, but the source and calculation basis of the baseline emission level Bi and target emission level Ti in Table 12 are not explained in the text, and the rationality of the weight setting cannot be verified.

Thank you for your comment. We are sorry we miss the source of the weight determination. We have added the source in Table 12 and explained the base year and target years on the lines 499-507. The data is collected from China environmental statistic reports and energy statistic year-books, etc. the targets are from the policies, development reports and related research.

The case study only selects a single integrated pipe gallery project, lacking comparative analysis with ordinary underground pipelines (water supply, drainage, gas pipelines) of different types and scales, and the universality of the model is insufficiently verified.

Thank you for your comment. The project is an urban underground pipeline network with seven major categories of municipal pipelines: water supply, heating, gas, electricity, tele-communications, stormwater drainage, and sewage, which is more complex than other single ordinary pipelines. This project is managed by an experienced company in China with good quality, so it is a representative case in China. Also, the research framework and methods are applicable for other cases.
In order to show the applicability of the model, we also discussed and compared the results with other research on the lines 694-724 in blue. During the comparison, the proposed model and weighting method in this paper can comprehensively analyze the impacts of the urban underground pipeline projects during the whole life cycle.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper addresses a very important topic.

Chapter 1 is very detailed. The question arises whether the introduction
could be shortened (e.g., lines 63 to 83).

In the PDF, it is noticeable that several figures have very little space
between them and the text (e.g., Figure 1, Figure 3, Figure 4). Increasing
the spacing would improve readability.

The labels in Figure 4 are very small and therefore difficult to read.
The labels should be enlarged. The individual diagrams could also be
presented as separate figures.

The content presents very interesting facts and results with appropriate
explanations, which together make a very good impression.

The cited sources are sufficient and relevant.

Author Response

This paper addresses a very important topic.

Thank you for your comment. Your affirmation is very encouraging.

Chapter 1 is very detailed. The question arises whether the introduction could be shortened (e.g., lines 63 to 83).

Thank you for your comment. We have modified the introduction section. With other reviewers’ comment that some references should be added, then the question background was shortened on the lines 65-90 in blue.

In the PDF, it is noticeable that several figures have very little space between them and the text (e.g., Figure 1, Figure 3, Figure 4). Increasing the spacing would improve readability.

Thank you for your comment. We are sorry that we did not notice the figure space. We have modified all the figures and make sure that there are enough spaces to show the figures.

The labels in Figure 4 are very small and therefore difficult to read. The labels should be enlarged. The individual diagrams could also be presented as separate figures.

Thank you for your comment. We have modified Figure 4 to ensure that the words and numbers are clear and big enough.

The content presents very interesting facts and results with appropriate explanations, which together make a very good impression.

Thank you for your comment. Your affirmation is very encouraging.

The cited sources are sufficient and relevant.

Thank you for your comment. Your affirmation is very encouraging.

Reviewer 3 Report

Comments and Suggestions for Authors

The article is interesting and follows the scope of Sustainability, due to a lifecycle assessment of urban underground pipeline projects and identifies the stages that contribute most to environmental impacts. It seems to contribute to the literature showing non-published content. However, it still needs some improvement regarding:

Abstract is missing a brief exposition of the methodology regarding the case study as well as some quantitative results of it.
The Introduction’s lines 38-83 need improved reference, a lot of statements are miscited, authors could use relevant and consolidated works for theoretical background and current studies (2024-2026) to support the novelty.
Besides, the sustainable development impact of the research based on governmental directives and programs must be added (clearly identify each one of the SDGs that your work contributed), addressing the research significance of the paper linked to the main goal.
Section 2, Lifecycle assessment framework, could be simply reduced to Figure 2 and 1-2 paragraphs referencing which LCA standard was used and the specificality the authors have used from references [10-16].
Section 2 and 3 should be merged as Methodology.
Some contents from Section 3 should be moved to the Results section, namely from Subsection 3.3 until the end of Section 3.
Section 4 should be named as Results and comprise the content from comment 6 and “The environmental impact assessment model”.
Section 5 should be Model Validation, and the Case Study must be referenced and briefly described in the Methodology section.
The Results are well presented and interpreted; however, there is no comparison over it to other published works, authors must add those comparisons using Introduction’s literature (improved) to support the narrative.
Authors must add another Section named Discussion, where the literature which has corroborated and/or contrasted with authors’ findings is presented regarding similar evaluation and/or different methodological approach for underground pipeline projects.
It will enrich your manuscript, in addition, based on your results and the literature search, discuss on:

The paper reads more like a methodological application paper than a novel LCA methods paper, so its contribution should be framed more carefully, clearly separate what is standard LCA practice from what is specifically new in this study.
Since weighting can strongly affect final rankings, the authors should explain why the chosen method is appropriate for Chinese urban infrastructure and whether alternative weighting schemes would change the outcome.
The identification of operation and maintenance, raw material production and processing, and construction as the main contributing stages is also useful for practice. However, the manuscript should explain why these stages dominate in this particular project, rather than simply listing the ranking.
If the case is intended to support broader generalization, then the manuscript should justify representativeness and discuss how local conditions may limit transferability.

Conclusions could be synthetized by avoiding repetitions from Results and Discussion; besides, authors should highlight the limitations of the study.
Verify references formatting according to the journal’s template instructions.

In summary, while the technical execution is strong, the manuscript would benefit from improved organization, methodological framing, and deeper discussion.

Author Response

Abstract is missing a brief exposition of the methodology regarding the case study as well as some quantitative results of it.

Thank you for your comment. The case is used to verify the applicability of the model and the quantitative results are shown in the abstract on the lines 24-32 in blue. We used the original data of the project to calculate the result based on the LCA model.

The Introduction’s lines 38-83 need improved reference, a lot of statements are miscited, authors could use relevant and consolidated works for theoretical background and current studies (2024-2026) to support the novelty.

Thank you for your comment. We have added some relevant and latest research to analyze the current situation on lines 76-77 and 83-85 in blue.
Martinez, A.; Miller, S.A. Life Cycle Assessment and Production Cost of Geopolymer Concrete: A Meta-Analysis. Resources, Conservation and Recycling. 2025, 215: 108018.
Dada, O.I.; Liyanage, T.U.H.; Chi, T.; et al. Towards Sustainable Agroecosystems: A Life Cycle Assessment Review of Soil-Biodegradable and Traditional Plastic Mulch Films. Environmental Science and Ecotechnology. 2025, 24: 100541.
Xu, H.; Kim, J.I.; Chen, J. Improved Framework for Estimating Carbon Emissions from Prefabricated Buildings During the Construction Stage: Life Cycle Assessment and Case Study. Building and Environment. 2025, 272: 112599.
Shen, K.; Cheng, C.; Li, X.; et al. Environmental Cost-Benefit Analysis of Prefabricated Public Housing in Beijing. Sustainability. 2019, 11(1):207.
Ullah, K.; Tanoli, W.A. A Lifecycle BIM-Based Framework for Safe and Efficient Underground Utility Management. Buildings. 2026, 16: 1619.

Besides, the sustainable development impact of the research based on governmental directives and programs must be added (clearly identify each one of the SDGs that your work contributed), addressing the research significance of the paper linked to the main goal.

Thank you for your comment. We have fully explained the contributions of the paper to the government policy making and SDGs on the lines 127-137 in blue.
The proposed model considers the lifecycle process of urban underground pipeline pro-jects with quantification and each stage and impact factor can be analyzed. The government and managers can find out which stages and factors have the most impacts. Then, the government can propose environmental standards and regulatory policies according to the model. The paper plays a crucial supporting role in achieving green and low-carbon development of urban infrastructure and realizing the sustainable development goals (SDGs). According to the impacts, the government and managers can focus on the unrenewable energy consumption and the factors that affect the climate change and water us-age, etc., and will take actions to reduce the impacts. These actions are helpful to achieve the SDGs, especially the 7th, 9th, 13th and 15th goals.

Section 2, Lifecycle assessment framework, could be simply reduced to Figure 2 and 1-2 paragraphs referencing which LCA standard was used and the specificality the authors have used from references [10-16].

Thank you for your comment. We have explained the development of the LCA framework with some research on the lines 139-151. Now, the mature LCA framework in Figure 2 is based on ISO. Also, we explained each process of the framework on the lines 155-183, which is the core contexts of the framework. Then the research framework in Figure 3 is based on the LCA framework on the lines 139-141, 146-151, and 184-198 in blue. Therefore, Figure 1 show the basic theory of LCA and Figure 2 shows more details of our research.
We agree with the reviewer that the framework can be simply reduced to Figure 2, but to clearly show the theory basis and the research idea, we think it would be better keeping both Figure 1 and 2.

Section 2 and 3 should be merged as Methodology.

Thank you for your comment. Based on the research framework, Section 3, 4 and 5 are the main contexts of the goal and scope definition, lifecycle inventory analysis, lifecycle impact assessment, and interpretation. Section 2 is a theory introduction and show the research framework. Based on Section 2, we analyzed each process in the following sections.
We agree with the reviewer that Section 2 and 3 are theory and methodology part, but to clearly follow the process of LCA, we think it would be better separating Section 2 and 3. Also, if we merge two sections, it would be very long as one section.

Some contents from Section 3 should be moved to the Results section, namely from Subsection 3.3 until the end of Section 3.

Thank you for your comment. Based on the research framework, Section 3, 4 and 5 are the main contexts of the goal and scope definition, lifecycle inventory analysis, lifecycle impact assessment, and interpretation. Section 2 is a theory introduction and show the research framework. Based on Section 2, we analyzed each process in the following sections. Therefore, Section 3 is not the result part. Section 3.3 is the middle process of the research. The database is used to analyze the results in Section 5.

Section 4 should be named as Results and comprise the content from comment 6 and “The environmental impact assessment model”.

Thank you for your comment. Based on the research framework, Section 3, 4 and 5 are the main contexts of the goal and scope definition, lifecycle inventory analysis, lifecycle impact assessment, and interpretation. Section 2 is a theory introduction and show the research framework. Based on Section 2, we analyzed each process in the following sections. Therefore, Section 4 is not the result part. It is the middle process of the research and we built the assessment model to analyze the impact in Section 5. Then, all the data and model from Section 3 and 4 are used in an urban underground pipeline project in Section 5, so Section 5 are the result part.

Section 5 should be Model Validation, and the Case Study must be referenced and briefly described in the Methodology section.

Thank you for your comment. The title of Section 5 is modified into Case study and model validation. Also, the case study in mentioned in Figure 2 and on the lines 195-198 in blue.

The Results are well presented and interpreted; however, there is no comparison over it to other published works, authors must add those comparisons using Introduction’s literature (improved) to support the narrative.

Thank you for your comment. In order to show the applicability of the model, based on the comment 10, we discussed and compared the results with other research on the lines 694-724 in blue. During the comparison, the proposed model and weighting method in this paper can comprehensively analyze the impacts of the urban underground pipeline projects during the whole life cycle.

Authors must add another Section named Discussion, where the literature which has corroborated and/or contrasted with authors’ findings is presented regarding similar evaluation and/or different methodological approach for underground pipeline projects.

Thank you for your comment. Based on the comment 9, we discussed and compared the results with other research on the lines 694-724 in blue. During the comparison, the proposed model and weighting method in this paper can comprehensively analyze the impacts of the urban underground pipeline projects during the whole life cycle.

It will enrich your manuscript, in addition, based on your results and the literature search, discuss on:

The paper reads more like a methodological application paper than a novel LCA methods paper, so its contribution should be framed more carefully, clearly separate what is standard LCA practice from what is specifically new in this study.

Thank you for your comment. According to the discussion and comparison, we proved that the proposed model and weighting method in this paper can comprehensively analyze the impacts of the urban underground pipeline projects during the whole life cycle on the lines 718-724 in blue. Also, the research on environmental impact assessment of urban underground pipelines seldom considers all the common impacts. We followed the LCA theory and analyzed all the common impacts and calculated the related factors, which is the main contribution of this research.
We admit that the paper looks like a methodological application paper because we follow the LCA framework, but the data and results during the analysis are based on the character of urban underground pipelines and the results are also meaningful for the government and managers.

Since weighting can strongly affect final rankings, the authors should explain why the chosen method is appropriate for Chinese urban infrastructure and whether alternative weighting schemes would change the outcome.

Thank you for your comment. We analyzed and compared three weighting methods, i.e., the expert scoring method, the willingness-to-pay (WTP) method, and the target-distance method on the lines 483-503. We also explained the reason why the target-distance method is suitable for Chinese urban infrastructure on lines 495-502 in blue.
The target-distance method not only reflects China’s strategic orientation in environmental governance but also allows for adjustments based on current policies. Also, the weights are dynamic with the policies and targets change. Therefore, the target-distance method is suitable to determine the weights based on China’s latest environmental policies. In this paper, 2020 is the base year because it is the ending year of the 13th Five-Year Plan and the beginning year of the 14th Five-Year Plan of China. Then, 2025 and 2030 are the target years because 2025 is the ending year of the 14th Five-Year Plan. Also, 2030 is the year of carbon peaking.

The identification of operation and maintenance, raw material production and processing, and construction as the main contributing stages is also useful for practice. However, the manuscript should explain why these stages dominate in this particular project, rather than simply listing the ranking.

Thank you for your comment. We have analyzed the results of different stages and added the reasons on the lines 669-680 in blue. Also, we made some implications for each stage in Section 5.3.

If the case is intended to support broader generalization, then the manuscript should justify representativeness and discuss how local conditions may limit transferability.

Thank you for your comment. This project case is managed by an experienced company in China with good quality, so it is a representative case in China. We use this case to show the applicability of the model, and the research framework and methods are suitable for other cases.
The explanation is mentioned on the lines 521-524 and 786-787 in blue.

Conclusions could be synthetized by avoiding repetitions from Results and Discussion; besides, authors should highlight the limitations of the study.

Thank you for your comment. The main findings are synthetized on the lines 789-805 in blue. Also, the limitations and future research is mentioned on the lines 809-815.

Verify references formatting according to the journal’s template instructions.

Thank you for your comment. We have double checked the format of references to meet the journal’s requirement.

In summary, while the technical execution is strong, the manuscript would benefit from improved organization, methodological framing, and deeper discussion.

Thank you for your comment. We have tried our best to modify and improve the paper according to the reviewer’s comments.

Reviewer 4 Report

Comments and Suggestions for Authors

Investigate the importance of establishing lifecycle inventory database through the inventory analysis
quantitative results of the evacuation of environmental impact should be added in the abstract
explain how the proposed model can be used in formulating environmental standards and regulatory policies.
The research frame work shown in figure 2 needs to be enhanced and visualized better than this in figure 2
The authors should cite equations 1 and 2 . also, all the not derived equations
What are the main creation to choose the impact factors are shown in Table 8.
What is the source of table 11
More analysis of the proposed model are required

Author Response

Investigate the importance of establishing lifecycle inventory database through the inventory analysis

Thank you for your comment. We have added the inventory database analysis and explained the importance of establishing lifecycle inventory database on the lines 291-265 in blue.

quantitative results of the evacuation of environmental impact should be added in the abstract

Thank you for your comment. The abstract is modified to show the quotative results on the lines 27-32 in blue.
The results indicate that the photochemical ozone creation potential (POCP), atmospheric particulate matters potential (APMP), and solid waste potential (SWP) have the most significant environmental impacts, and the total environmental impact values are 70, 104 and 83.9 capita equivalent, respectively. Moreover, the raw material production and processing, operation and maintenance, and construction stages are identified as the primary contributors to these environmental impacts, and the values are 17.5, 10.6 and 1.8 capita equivalent, respectively.

explain how the proposed model can be used in formulating environmental standards and regulatory policies.

Thank you for your comment. We have analyzed the value of the research and explained the contributions to the environmental standards and policies on the lines 127-131 in blue.
The proposed model considers the lifecycle process of urban underground pipeline projects with quantification and each stage and impact factor can be analyzed. The government and managers can find out which stages and factors have the most impacts. Then, the government can propose environmental standards and regulatory policies according to the model.

The research frame work shown in figure 2 needs to be enhanced and visualized better than this in figure 2

Thank you for your comment. We have modified Figure 2 with clear process introduction and explained the whole process of the framework on the lines 184-198 in blue.

The authors should cite equations 1 and 2 . also, all the not derived equations

Thank you for your comment. We have cited all the equations on the lines 533, 561, 578, 602, and 629 in blue.

What are the main creation to choose the impact factors are shown in Table 8.

Thank you for your comment. We have explained the types of the impacts and cited the reference on the lines 393-404 in blue.
Cao, X.; Li, X.; Zhu, Y.; et al. A Comparative Study of Environmental Performance Between Prefabricated and Traditional Residential Buildings in China. Journal of Cleaner Production. 2015, 109: 131-143.

What is the source of table 11

Thank you for your comment. The source of table 11 is from some research on China’s environmental impacts, which provides the basic data for the paper. Especially, Yang et al. analyzed a lot of environmental impacts in China and built the benchmark [25, 28-30].
Yang, J.; Liu B. Life Cycle Inventory Analysis of Chinese Steel Products. Journal of Environmental Science. 2002, (04): 519-522.
Xie, M.; Man, H.; Duan, H.; et al. Research Progress on the Life Cycle Impact Assessment Methods and Their Localization in China. Journal of Environmental Engineering Technology. 2022,12(6): 2148-2156.
Ding, N.; Lu, X.; Yang, J.; et al. Water footprint of coal production．Acta Scientiae Circumstantiae. 2016, 36(11): 4228-4233.
Ding, N.; Yang, J. Life Cycle Inventory Analysis of Fossil Energy in China. China Environmental Science, 2015, 35(5):1592-1600.

More analysis of the proposed model are required

Thank you for your comment. We analyzed the model and results, and also discussed and compared the results with other research on the lines 694-724 in blue. During the comparison, the proposed model and weighting method in this paper can comprehensively analyze the impacts of the urban underground pipeline projects during the whole life cycle.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have addressed all revisions and improved a lot the manuscript.