Route Selection and Alternatives Considered

Transcription

1 Route Selection and Ciarán Butler BE, MEngSc, CEng, MIEI 1. My name is Ciarán Butler and I am a Technical Director in RPS Consulting Engineers. I have been with RPS since 1996 and I manage the Energy Section of the Company. I have been the RPS Project Manager of the Corrib Onshore Pipeline project since RPS was appointed by Shell E&P Ireland Ltd. (SEPIL) in January, Qualifications & Experience 2. I qualified as a Mechanical Engineer in University College Dublin in I also graduated with a Masters of Engineering Science degree in I am a Chartered Engineer and a member of Engineers Ireland. 3. My relevant experience to this project includes management, engineering, planning and environmental responsibilities on a number of gas pipeline projects for Bord Gáis Éireann (BGE) from 1998 to RPS has extensive relevant experience on other infrastructure projects which has been applied to this project including: Natural gas pipelines including the Gas Pipeline to the West and the South- North Pipeline. Environmental Impact Statements for large scale linear development and infrastructure projects Local community consultation 2. RPS s Brief 5. RPS s Brief on the Corrib Onshore Pipeline project resulted from the recommendation of Peter Cassells in his Report and Recommendations from Mediation (2006). This was to: modify the route of the Onshore Pipeline in the vicinity of Rossport in order to address community concerns regarding proximity to housing. CB 1

2 3. Summary of Evidence 6. In my Witness Statement which was submitted at the 2009 Corrib Onshore Pipeline Oral Hearing, I explained the process used to identify what we considered to be the optimum route for the Corrib Onshore Pipeline (paragraphs 8 to 34). This was the pipeline route which was proposed in In 2009 I also outlined how the layout of the proposed Landfall Valve Installation (LVI) was chosen (paragraphs 56 to 69). 8. My objectives in this Witness Statement, are to : explain the basis for the pipeline route now proposed. explain the principal alternatives that were considered in developing the proposal which is now before An Bord Pleanála. explain the basis for the proposed mechanical arrangement of the LVI These issues are described in Chapter 3 of the revised Corrib Onshore Pipeline EIS. 4. Pipeline Route Now Proposed 9. In November, 2009 An Bord Pleanála added a new route selection criterion as follows: the routing distance for proximity to a dwelling shall not be less than the appropriate hazard distance for the pipeline in the event of a pipeline failure. The appropriate hazard distance shall be calculated for the specific pipeline proposed such that a person at that distance from the pipeline would be safe in the event of a failure of the pipeline This criterion is the principal constraint by which the pipeline route now proposed has been defined. 4.1 Identification of Pipeline Route Now Proposed Slide 1 Proposed Pipeline Route, 2009 Proposed Route and 2002 Approved Route 10. Slide 1 shows the pipeline route now proposed (red) and the pipeline route which was proposed in 2009 (blue). The 2002 approved route is also shown (black). It is clear that the main difference between the pipeline route now proposed and the 2009 proposed route is in the section between (2009) chainage points and The pipeline route that is now proposed is within Sruwaddacon Bay for this section which is tunnelled. 11. Given An Bord Pleanála s requirements with respect to what the Board termed an appropriate hazard distance for the pipeline route, the scope for the consideration of alternative pipeline routes between the indicated chainage points was very CB 2

3 limited. Accordingly, the detailed alignment of the pipeline route now proposed has been developed on the basis of optimising its distance from dwellings having regard to the proposed construction method. 12. The minimum distance from dwellings to the centreline of the proposed pipeline route is now 234m. This allows for a construction tolerance of +/-8m in the horizontal alignment of the proposed tunnel within Sruwaddacon Bay. 5. Alternative Construction Methods Considered 13. The main focus for the consideration of alternatives in the revised EIS was construction methods that would work in Sruwaddacon Bay. In November, 2009, the various construction options that had been identified as possibilities for constructing a pipeline in Sruwaddacon Bay were re-examined by RPS and SEPIL. This included significant input from specialist designers and contractors. 14. The main objective of this exercise was to identify a construction method for Sruwaddacon Bay which would not have a significant impact on this designated conservation site whilst at the same time balancing community and project considerations. It was considered that the proposed method should at least achieve the same low level of impact to the Bay as that which was predicted for the 2009 proposed route. 15. It was considered that the risk to the environment of Sruwaddacon Bay would increase as the extent of surface works within the Bay increased. Therefore, the extent of surface works for each option was considered in detail in order to minimise potential impacts. 16. The principal alternative construction methods examined for Sruwaddacon Bay were as follows: Open cut construction using the sheet piling in sections method Micro-tunnelling using the pipe jack method Segment lined tunnelling Slide 2 : Open cut construction using the sheet piling in sections method 17. The sheet piling in sections construction method was considered during the original route selection process. This method was developed further with input from specialist contractors to cater for the specific conditions in Sruwaddacon Bay. Sheet piling in sections was considered to be the open-cut method which would have least environmental impact. It would be used to install a steel sleeve pipe within which the gas pipeline and associated services would be installed later. The area directly impacted by this method at any particular time would be approximately 300m long and approximately 15m wide. The overall area of impact within Sruwaddacon Bay would be approximately 4.6km long x 15m wide. There would be significant challenges in the vicinity of the main channel close to Glengad using this method. Also, there would be a need for open cut construction at Glengad and Aghoos where the pipeline route crossed the high water mark. CB 3

4 Slide 3 : Pipe-Jacking Option 18. The pipe-jacking method of micro-tunnelling was also examined further. It is considered that the longest tunnel which could be constructed using this method in Sruwaddacon Bay and not require an intermediate pit is 1.2km. This method was therefore considered in combination with segment lined tunnelling and in combination with the open cut method described above. In both cases, there would be a much higher likelihood of surface works than with the proposed method. The optimal configuration using pipe-jacking was considered to comprise a 1.2km pipe jack tunnel starting at Glengad. Segment lined tunnelling would be used from Aghoos, with both tunnels meeting below the surface. This would involve a docking procedure where one tunnel would be bored into the end of the other tunnel at a point under the surface of Sruwaddacon Bay. However, there would still be the risk of an intervention pit. Overall, this trenchless method does not offer any significant advantages over the proposed construction method. Slide 4: Segment Lined Tunnelling 19. The proposed construction method is segment lined tunnelling. This method was selected as it is the only construction method that can be used without the requirement for surface works in the Bay. It is the only tunnelling method that can be used over such a long distance without the requirement for intermediate pits. The risk of there being a requirement for surface intervention with segment lined tunnelling is extremely low. Therefore, this method all but eliminates the risk of impact to Sruwaddacon Bay. 20. In the following sections of my statement, I will outline some of the main alternatives considered in the design of the tunnel. Mr. Tim Jaguttis (de la Motte & Partners) will answer any detailed questions regarding the design of the tunnel. 5.1 Size of Tunnel Slide 5: Cross Sections of Tunnel 21. The size of the tunnel has been optimised having regard to the following: 8 10 personnel will work within the tunnel at all times during its construction. The tunnel must be ventilated and otherwise fitted out to ensure that personnel can carry out their work safely. Concrete segments which are used to construct the tunnel must be transported through the tunnel on a railway system and erected using machinery towards the rear of the tunnel boring machine. Installation of the gas pipeline and associated services within the tunnel will involve manned activities. The proposed tunnel will have an inside diameter of 3.5m and an external diameter of 4.2m. This is considered to be the minimum acceptable size for a tunnel along the proposed alignment within Sruwaddacon Bay. A larger tunnel CB 4

5 was not considered on the basis that the overall impact of tunnel construction should be minimised. 5.2 Alternative Approaches to Segment Lined Tunnelling 22. Having selected segment lined tunnelling as the preferred construction method, it was then considered how to minimise the potential for environmental impacts from the tunnelling process. Slide 6 : Segment lined tunnelling from both sides 23. It was estimated that the overall construction programme could be reduced by approximately 6 months if the proposed tunnel was bored from both ends i.e. by using two tunnel boring machines. However, this approach would have required a tunnelling compound at Glengad similar in size to that proposed at Aghoos. It would also have resulted in significant additional traffic on the L1202 between Glengad and Pollatomish. 24. By tunnelling from both ends, the tunnelling process would have involved an additional and complex docking procedure. This is where one tunnel would be bored into the end of the other tunnel at a point under the surface of Sruwaddacon Bay. For this to take place, it would be necessary for one of the tunnels to be smaller in diameter to allow docking to take place. This option was not considered to be optimal as there would be an increased risk of surface intervention. 25. It was considered therefore that the potential environmental impacts on the local community (including noise, visual and traffic impacts) could be minimised by tunnelling from Aghoos only. Also, by tunnelling from one side only, the overall technical risk of the process would be reduced. 5.2 Vertical Alignment of Tunnel 26. The proposed vertical alignment of the tunnel may vary between a minimum cover of 5.5m and a maximum depth of 10m below the indicated centreline. On this alignment, the tunnel will be mainly through the superficial deposits overlying bedrock within Sruwaddacon Bay. However, due to the profile of the local geology, tunnelling will be through rock for a distance around the starting pit and reception pit. Overall, it is estimated that approximately 80% of the tunnelling will be through sands and gravels and approximately 20% will be through rock. 27. A deeper vertical alignment whereby the tunnel would be bored entirely through rock was also considered. This option had the significant disadvantage of adding a further estimated 5-6 months to the overall construction programme with consequences in terms of the duration of various impacts. It would also require additional manned activities within the tunnel due to the higher rate of wear and tear on the tunnelling machine. CB 5

6 5.3 Alternatives to Grouting Tunnel 28. Once the tunnel is completed and all services including the gas pipeline have been installed, it is proposed to fill the void space within the tunnel with cement grout. This will ensure that the gas pipeline and associated services are safe and fully protected for the duration of their operation. The fully grouted configuration will also ensure the long term integrity of the tunnel structure. Spare services are proposed within the tunnel to ensure that should there be a need, these can be used. This is a consequence of grouting the tunnel. 29. Alternative options of partially grouting the tunnel, filling with water or leaving the tunnel open were considered. However, these options were not as favourable in terms of overall pipeline protection and operational issues. This is described in more detail in Section of the revised EIS. 6. Management of Tunnelling Arisings Slide 7 Materials Management Plan Summary 30. The proposed tunnel under Sruwaddacon Bay will be approximately 4.9km long and 4.2m in diameter. Consequently, approximately 68,000m 3 of material will be generated during tunnelling. It is estimated that approximately 80% of this material will be mainly sands and gravels with some silts. The remaining 20% will be rock cuttings. 31. Alternative outlets and disposal options for surplus materials arising during the construction of the Corrib Onshore Pipeline project were examined by the project team. This is outlined in Appendix S4 of the revised EIS and summarised on Slide 7. The preferred strategy for managing this material is to maximise re-use and to minimise disposal. This is in accordance with National and Regional Waste Management policy which has at its core the principles of the European Waste Management Hierarchy. 32. It is estimated that at least 35% of tunnelling arisings can be used on the Corrib Onshore Pipeline project, for example during the construction of the stone road and the pipeline stringing area at Aghoos. Our analysis to-date shows that most of the tunnelling arisings and other materials arising during the demobilisation of compounds will be suitable for use in the construction industry or for use in quarry restoration. 33. SEPIL has had preliminary discussions with a number of organisations regarding surplus materials arising during the construction of the proposed pipeline. These discussions have been positive. Subject to timing, and the volume and specification of material that may be required by third parties for other projects, it is confidently expected that a large proportion of surplus material arising on the Corrib Onshore Pipeline project will be re-used by third parties. Materials re-used regardless of destination will be subject to regular testing and sampling to ensure that quality is maintained. CB 6

7 34. It is estimated that approximately 17,000 tonnes of material such as silts and bentonite residues will not be suitable for re-use on construction projects (see Table 4.1 in Appendix S4 of the revised EIS). This material will need to be disposed of at an authorised waste management facility or facilities. Derrinumera Landfill in Co. Mayo has been identified as the preferred outlet for this material. 35. SEPIL s proposed contingency measure for disposing of surplus materials arising that cannot be used by the Corrib Onshore Pipeline project, other identified construction projects or sites permitted to accept such material, is to transport this material to a licensed disposal site. Two licensed construction and demolition landfills operated by Murphy Environmental Ltd. have been identified as this safeguard solution. These are the only existing facilities in Ireland that have sufficient licensed capacity to accept all materials that could potentially arise from the Corrib Onshore Pipeline project. It must be emphasised however that the disposal of potentially re-usable materials at landfill will only take place as a last resort. 7. Mechanical Arrangement of Landfall Valve Installation (LVI) Slide 8 Proposed Mechanical Arrangement of LVI 36. The proposed mechanical arrangement of the LVI is the same as that which was proposed in With this arrangement, two in line Shut Down Valves (V3 and V4), are located on a 16 inch (406mm) bypass of the mainline. The Shut Down Valves will be responsible for ensuring that the Maximum Allowable Operational Pressure (MAOP) in the Onshore Pipeline is 100barg. During normal operation, the 20 isolation valve (V1) which is on the mainline will be closed. This means that during normal operation gas will always flow through the bypass and therefore through the Shut Down Valves. 37. An alternative mechanical arrangement was considered whereby the Shut Down Valves would be located on the mainline. This option was referred to by An Bord Pleanála as the straight pipe option. With this configuration, gas would normally flow through the mainline and not through a bypass arrangement as proposed. 38. A detailed assessment of the alternative options was carried out by JP Kenny for SEPIL. This is included as Appendix Q 4.4 of the revised EIS. This assessment has had regard to relevant codes and standards of design and operation. It has also incorporated additional requirements of Shell s own standards of design and operation. The track record of relevant proprietary equipment has also formed part of the assessment. It is considered that the proposed arrangement represents best industry practice for this type of installation. 39. The proposed mechanical arrangement of the LVI is considered to be superior to the straight pipe option for the following reasons: There is little or no industry experience with 20 inch full bore valves in High Pressure Protection Systems. This is an important consideration for SEPIL. CB 7

8 It will be necessary to carry out internal inspections of the Corrib Gas Pipeline periodically. This will be done using pipeline inspection devices commonly known as pigs. It is considered that in-line piggable High Pressure Protection Valves are not best practice. This is because the integrity of the valves could be compromised due to mechanical damage to the valve seals during pigging. The proposed bypass arrangement allows the pipeline to be pigged without in any way compromising the integrity of the Pressure Limiting Valves. The straight pipe option is not considered by SEPIL to represent best industry practice. It does not meet Shell s standards of design. The straight pipe option gives a negligible reduction in the level of individual or societal risk at the LVI when compared to the proposed bypass arrangement (see Appendix Q 6.4, Attachment B Sensitivity Predictions (Figures 18 and 19)). 40. Mr. John Gurden (JP Kenny) will respond to questions on the detailed mechanical design of the LVI. Mr. Phil Crossthwaite (DnV) will respond on detailed questions regarding the Quantified Risk Assessment. 8. Conclusions Slide 9 Proposed Pipeline Route 41. My objective in this statement was to explain the principal alternatives that were considered in developing the proposal which is now before An Bord Pleanála. In summary: The proposed route meets An Bord Pleanála s new criterion with respect to proximity to occupied dwellings. This was the principal constraint by which the specified section of the pipeline route has been defined. The route is at least 234m from existing dwellings. There is a significantly greater separation distance between existing dwellings and the route now proposed than was the case with the previously approved route (70m) and the pipeline route proposed in 2009 (140m). The proposed pipeline development minimises potential impact to environmentally sensitive and designated conservation sites. This has been achieved through the proposed use of segment lined tunnelling under Sruwaddacon Bay. By tunnelling from Aghoos only, the potential impacts on the local community in the more populated areas of Glengad and Pollatomish have been minimised. The design of the proposed tunnel has been developed on the basis of minimising risk at every level. It is proposed to maximise the use of materials arising from the proposed tunnelling activities on the Corrib Onshore Pipeline project and, subject to relevant agreements and approvals being in place, on identified third party construction projects. The contingency plan for materials arising during the CB 8

9 construction of the proposed pipeline is to transport all materials to a licensed facility or facilties. Two facilities have been identified which have sufficient licensed capacity for all such materials arising. These will only be used as a last resort. It is considered that the proposed mechanical arrangement for the LVI represents best industry practice for this type of installation. This concludes my statement. Thank you. CB 9

10 By Ciarán Butler (An Bord Pleanála Application Reference No.: 16.GA0004)

11 Proposed Pipeline Route, 2009 Proposed Route and 2002 Approved Route (Figure 3.4, Corrib Onshore Pipeline EIS, Volume 1, Main Report) 1

12 Open cut construction at Glengad Landfall Travelling construction area on surface of Bay 300m x 15m Overall disturbed area: 4.6km x 15m Open cut construction at Aghoos Landfall Construction compound and Pipe Stringing Area at Aghoos Alternative Construction Method - Sheet Piling in Sections 2

13 Micro-tunnel / Pipe Jack Starting Pit at Glengad Docking Point or Intermediate Pit in Bay 12m x 25m 2.0m Ø Tunnel 4.2m Ø Tunnel Micro-tunnel / Pipe Jack 2.0m Ø, 1.2km Docking (sub-surface) Segment Lined Tunnel 4.2m Ø, 3.7km Tunnelling compound and Pipe Stringing Area at Aghoos Alternative Construction Method Pipe Jacking Option 3

14 Reception Pit at Glengad Segment Lined Tunnel 4.2m Ø, 4.9km Tunnelling compound and Pipe Stringing Area at Aghoos Proposed Construction Method Segment Lined Tunnelling 4

15 Cross Sections of Tunnel (Figure 5.5, Corrib Onshore Pipeline EIS, Volume 1, Main Report) 5

16 Tunnelling compound at Glengad 3.5m Ø Tunnel 4.2m Ø Tunnel Docking (sub-surface) Segment Lined Tunnel 3.5m Ø, 3.0km Docking Point Segment Lined Tunnel 4.2m Ø, 1.9km Tunnelling compound and Pipe Stringing Area at Aghoos Alternative Construction Method Tunnelling from Both Sides 6

17 Materials Management Plan summary 7 (Corrib Onshore Pipeline EIS, Volume 2, Appendix S4, Figure 5.4)

18 Proposed Mechanical Arrangement of LVI 8 (Figure 4.5, Chapter 4, Corrib Onshore Pipeline EIS, Volume 1, Main Report)

19 Proposed Pipeline Route 9 (Figure 1.1, Corrib Onshore Pipeline EIS, Volume 1, Main Report)