Proposal for Northern Extension of Northolt Tunnel sift report
Yüklə 0,76 Mb. Pdf görüntüsü
|
- Bu səhifədəki naviqasiya:
- Location: Colne Valley OPTIONS CONSIDERED: Option A The Proposed Scheme as submitted in the hybrid Bill
- Above ground section between Northolt and Chiltern tunnels placed underground in bored tunnels with provision for connection spurs to Heathrow
- QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG
`Code 1 -
Accepted Uncontrolled when printed INTERNAL INFORMATION Northern Extension of Northolt Tunnel SIFT Report
C222-ATK-DS-REP-020-000034 Revision – P06
Page 49
Uncontrolled when printed INTERNAL INFORMATION
Key Sustainability Issue Topic STAGE: Constructio n or Operation EDA Considered (incl. Topic and Ref no.) Comment QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG pochard for breeding, and habitat used by corn bunting and coral root; effects that are assessed as significant at the county/ metropolitan level.
1.1.6
Construction The Scheme through will pass through habitats used by otter, watervole, bats, breeding and wintering birds, reptiles and great crested newts, which could result in significant adverse effects at the county/ metropolitan level. Op
No significant effects have been identified for the operational phase. o The tunnel section passes under the majority of the features listed in the base case and has no impact on them.
Overall the operational impact of this option is significantly reduced compared to Option A. +++ As Option B.
Water and flood risk Const
WR2, WR3, WR4, WR6 Construction within the lakes has the potential to generate impacts on water quality which could lead to a risk of a significant adverse effect. 1.1.7
If ground fissures connect the working area of the Proposed Scheme directly to very high value groundwater receptors such as Public Water Supply, the impact of even low levels of turbidity could cause the closure of a source due to the high quality required to be met for Public use. This risk is especially the case where the Colne Valley viaduct piers are sited within the areas designated SPZ1 TH177 and SPZ1 TH174 and where the SPZ1 TH027 will be intercepted by the retaining walls for the Tilehouse Lane cutting. If a PWS was forced to shut down this would be a major impact and will o The tunnel section passes under the majority of the surface water features listed in the base case and has no impact on them.
The majority of the tunnel from Ch 023+750 northwards passes through SPZ1, with two small sections in SPZ2. These are at Wyatt’s Covert Caravan Site and a section from the Hillingdon Outdoor Activity Centre to the Harvil Road.
Construction of the tunnel and cavern to accommodate the Heathrow spur turnouts below the water table and in SPZ1/2 has the potential to alter the risks to groundwater flows and licensed abstractions providing key potable water supplies. Although the programme of works in SPZ1 is longer than Option A, the work would be focussed in one or two areas at a time and the risks in those areas -- As Option B. However, avoidance of large caverns for the turnouts reduces potential impacts upon groundwater compared to Option B. --
`Code 1 -
Accepted Uncontrolled when printed INTERNAL INFORMATION Northern Extension of Northolt Tunnel SIFT Report
C222-ATK-DS-REP-020-000034 Revision – P06
Page 50
Uncontrolled when printed INTERNAL INFORMATION
Key Sustainability Issue Topic STAGE: Constructio n or Operation EDA Considered (incl. Topic and Ref no.) Comment QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG QUALITATIVE IMPACT DESCRIPTION and/or QUANTITIVE ASSESSMENT RATI NG therefore result in a significant adverse effect. 1.1.8
the potential to obstruct some flood flows temporarily during the construction works resulting in moderate impacts on flood risk to very high value receptors with a resulting large and significant adverse effect.
better defined and this may reduce the need for simultaneous closure of groundwater sources. The tunnels’ vertical alignment would avoid the need for multiple holes penetrating through the shallow aquifer into the deep aquifer. A deeper alignment may be preferred if it avoids the main intake sections of the water supply boreholes, though any change would be limited due to rail gradient requirements.
Groundwater mitigation measures would still be required although the maximum flow requirement may be reduced.
Groundwater quality in the vicinity of Shaft “E2” may be affected by contamination from New Years Green Landfill although the draft CoCP measures would address this.
The tunnel would occlude more of the effective aquifer than the proposed, Option A pile groups. Potential extra drawdown and loss of peak output of up to 40% could occur at Potable Water Supply source. A new water supply borehole immediately south west of the tunnels could be a suitable mitigation measure. A deeper alignment may be preferred if it then avoids the main fissures and intake sections of the water supply boreholes.
The flood risk to temporary works would be less than Option A since there are fewer above ground works in the flood plain Op With careful management of viaduct drainage into the surface water bodies, no operational impacts have been identified. o The need for viaduct drainage passing directly into surface water bodies would avoided. No operational impacts have been identified. o No operational impacts have been identified. o Creating sustainable communities Air quality Const
There will be substantial adverse impacts along Swakeleys Road, between Harvil Road and the A40, at a number of receptors assessed for NO2 as a consequence of construction traffic which are significant.
o
construction traffic associated with the removal of surplus excavated material from site could be severely affected. A detailed assessment would need to be undertaken in order to fully assess the implications of the additional construction traffic on air quality. --
As Option B. --
Yüklə 0,76 Mb. Dostları ilə paylaş:
|