Don’t bother about that now

Environmental aspects of the 51m consultation response, part 10

I am currently considering some of the comments that Southdowns Environmental Consultants Ltd has raised in Appendix 18 to the 51m alliance response to the public consultation (available here); at the moment I am considering issues that concern the extent of the impact on dwellings of noise from HS2. In my previous blog Leave it out! (posted 16 Oct) I looked at “noise receptors” that, according to Southdowns, have not been included in the assessment made by HS2 Ltd for the public consultation. In this present blog I will look at “noise sources” that have not been considered.

The Southdowns report points out that the analysis in the AoS only considers the impacts of pass-by noise from trains running on the surface. The report says:

“Other potential sources of adverse noise and vibration impact at both residential and non-residential receptors include: airborne noise from vent shafts, train and infrastructure depots, line-side equipment and other fixed plant; ground-borne noise and vibration from trains running in tunnels; surface and sub-surface construction noise and vibration.”

The general promise in paragraph 3.1.7 on page 43 of Appendix 5 of the AoS (available here) is that “all potential noise and vibration impacts” will be “fully assessed at EIA stage” and so should cover all of the noise sources listed by Southdowns. However, the AoS also offers the following specific comments, with the AoS paragraph and page number in Appendix 5 in brackets:

On airborne noise from vent shafts

“HS1 and the Jubilee Line Extension experience indicates that impacts can be avoided if vent shafts are built with appropriate mitigation. Crossrail will also feature noise-controlled vent shafts. The approach to HS2 TVS noise would adopt best practice for noise control. Past experience has shown that the majority of potential noise impacts can be avoided through the use of effective planning/design and other noise mitigation measures” (8.4.3, page 53).

On noise from depots (and stations)

“The following sources of noise from HS2 stations and depots have the potential to cause impacts at sensitive locations in proximity to the proposed stations and depots:

  • Passenger and maintenance trains accessing stations or depots;
  • Fixed plant installations at stations or depots e.g. wheel lathes, CET (Controlled Emissions Tanking) units, wash plant etc;
  • Mobile plant and maintenance activities not considered a constant noise source e.g. forklift trucks, hand tools etc;
  • Local road traffic accessing stations and depots, and changes to local road infrastructure; and
  • Public Address (PA) systems” (8.3.1 on pages 52 and 53).

“However, past experience has shown that the majority of these impacts can be avoided or minimised to a large degree through the use of effective planning/design and other noise mitigation measures” (8.3.2 on page 53).

On noise from line-side equipment and other fixed plant

These potential sources of noise are only discussed in the AoS where they are located at stations and, in that case, are covered by the quotations from paragraphs 8.3.1 and 8.3.2 given above.

On ground-borne noise and vibration from trains running in tunnels

This topic is covered by twelve paragraphs in Appendix 5 of the AoS (2.4.3 and 3.1.6 on page 42, and section 9 on pages 54 and 55), so the following is a representative selection.

“The design at this early stage of a development provides insufficient detail to undertake a quantitative assessment, however, substantial experience from other projects, particularly HS1, enables a robust qualitative assessment to be made” (9.1.1 on page 54).

“Experience from HS1 and international guidance suggests that, without any mitigation, ground-borne noise and vibration impacts from HS2 could occur up to 100m from London tunnels and up to 200m from country tunnels, the difference reflecting the attenuating effects of London Clay and the relatively slower line speeds through London. However, HS1 and other international high speed rail experience suggest that potential vibration and ground-borne noise impacts could be avoided” (9.2.1 on pages 54 and 55).

“… airborne noise is the dominant issue for surface sections of line; and ground-borne noise is the key issue for tunnelled sections” (9.3.1 on page 55).

“Assuming 260km/h operational speeds in twin bore London tunnels and use of slab track, optimised to mitigate ground-borne noise and vibration, HS1 has shown that high speed rail can operate under densely populated residential areas with no adverse effects” (9.3.3 on page 55).

“Assuming 320 km/h operational speeds, with the provision of slab track and the alignment of the single bore tunnels under the Chilterns through chalk, there is a risk of adverse ground-borne noise and vibration effects to both residential and other noise sensitive resources located within 200m of the HS2 proposed alignment” (9.3.5 on page 55).

“Where properties may experience adverse effects based on the above, mitigation would first be assessed by further optimisation of the track design … where this is not practicable, further consideration would be given to the tunnel alignment or alternatively mitigation may be provided at the receiver” (9.3.6 on page 55).

Southdowns view about possible problems in the Chilterns is summed up in the following paragraph (5.8.7) from Appendix 18:

“Of particular concern is the risk of adverse effects to residential and other noise sensitive receptors within 200m of the proposed tunnel alignment under the Chilterns through chalk for the base engineered case with slab track. As the AoS indicates, there is limited data available for the mitigation of vibration from high speed trains travelling in tunnels and the benefits of ballast track with under ballast mats or floating slab may not be sufficient to remove adverse effects, albeit undefined. Further consideration of the tunnel alignment or mitigation at the receiver is proposed in the AoS as alternative mitigation options, although the latter mitigation option is not specified in further detail.”

On construction noise and vibration

“Construction noise has not been appraised as it is not appropriate at this stage of the Project, however such matters would be addressed as part of the HS2 Code of Construction Practice” (3.1.5 on page 42).

“The degree of ground-borne noise and vibration mitigation that is reasonably practicable during the construction of railway tunnels is constrained and hence it is likely that some level of short term adverse effect would arise during construction” (9.3.8 on page 55).

On the basis of all of these extracts from the AoS, I think that the charge should not be that the AoS fails to consider these additional noise sources, since clearly it does, but that it has failed to quantify the effects of these sources to inform the public consultation. In short, HS2 Ltd has failed to do the necessary work.

In the next blog I will discuss another issue in the Southdowns report that has not been mentioned previously in my blogs.

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