`Code
1 -
Accepted
Uncontrolled when printed
INTERNAL INFORMATION
Northern Extension of Northolt Tunnel SIFT Report
Northern Extension of Northolt Tunnel SIFT Report
C222-ATK-DS-REP-020-000034
Revision – P06
Page 47
Uncontrolled when printed
INTERNAL INFORMATION
Location:
Colne Valley
OPTIONS CONSIDERED:
Option A
The Proposed Scheme as submitted in the hybrid Bill
(Northolt Tunnel to West Ruislip/ Viaduct across the Colne
Valley/ Chiltern tunnel east of M25 between jnc 16 and
17)
Option B
Above ground section between Northolt and Chiltern tunnels
placed underground in bored tunnels with provision for
connection spurs to Heathrow
Option C
As per option B but with no passive provision for a connection
to Heathrow
OPTION DESCRIPTION
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
century garden at Denham Grove (De Vere
Hotel) (moderate adverse effect);
• Buried archaeological remains of potential
prehistoric date and of low value off
Tilehouse Lane (moderate adverse effect);
and
• Buried remains of a World War II searchlight
battery at Corner Hall (moderate adverse
effect)
Op
Operational impacts have been identified for Savay
Farm (an asset grouping of high value) and a
scheduled monument located south of Savay Farm
as a consequence of a change in setting related to
operational noise. This will constitute a medium
adverse impact resulting in a major adverse effect.
o
There are no impacts associated with the operation of
Option B.
+
As Option B.
+
1.1.3
Biodiversity
Const
EC1,
EC2,EC4,
EC5, EC7,
The viaduct passes through the Mid Colne Valley Site
of Special Scientific Interest (SSSI) resulting in the
loss of ancient woodland and wetland, which are
designating features of the site; effects that are
assessed as significant at the national level.
The combined effect of woodland, wetland and
grassland loss and disturbance of the
breeding bird assemblage will result in a permanent
adverse effect on the integrity of the Mid Colne
Valley Site of Metropolitan Importance that will be
significant at the county/metropolitan level.
Land required for construction within the Tilehouse
Gravel Pits Biological Notification Site (BNS) will
result in disturbance to birds having a permanent
effect on the integrity of the site that is significant at
the county/metropolitan level.
1.1.4
About 0.9ha (19%) of the River Colne east of
Denham BNS is within land required for construction
of the Proposed Scheme where National Grid
overhead power lines will be realigned. This will
o
The tunnel section passes under the majority of the
features listed in Option A (except at the vent shaft
locations, see below) and has no direct impact on them.
Depending on tunnel depth and construction, there are
potential risks to groundwater sensitive features, such as
the River Colne and the lakes themselves.
The proposed vent shafts located at c29+400 and c26+400
are not located within any designated site. The
construction of the vent shafts may lead to the loss of
broadleaved plantation woodland, hedgerows and arable.
Overall the construction impact of this option is
significantly reduced compared to Option A.
+++ As Option B.
+++
`Code
1 -
Accepted
Uncontrolled when printed
INTERNAL INFORMATION
Northern Extension of Northolt Tunnel SIFT Report
Northern Extension of Northolt Tunnel SIFT Report
C222-ATK-DS-REP-020-000034
Revision – P06
Page 48
Uncontrolled when printed
INTERNAL INFORMATION
Location:
Colne Valley
OPTIONS CONSIDERED:
Option A
The Proposed Scheme as submitted in the hybrid Bill
(Northolt Tunnel to West Ruislip/ Viaduct across the Colne
Valley/ Chiltern tunnel east of M25 between jnc 16 and
17)
Option B
Above ground section between Northolt and Chiltern tunnels
placed underground in bored tunnels with provision for
connection spurs to Heathrow
Option C
As per option B but with no passive provision for a connection
to Heathrow
OPTION DESCRIPTION
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
result in a permanent adverse effect on the integrity
of site that is significant at the county/metropolitan
level.
Denham Country Park LNR will also be affected
during construction. Approximately 10ha (52%) of
this site is within land required for construction of
the Proposed Scheme where National Grid overhead
power lines will be realigned. This extent of habitat
loss is a high proportion of the LNR and it will result
in a permanent adverse effect on site integrity that is
significant at the district/borough level.
In the Fray’s Valley Local Nature Reserve,
approximately 4.2ha (6% of the LNR) of woodland
and grassland will be removed where National Grid
power lines will be realigned. The extent of habitat
loss is relatively small in relation to the site’s size,
however, as part of the precautionary assessment, it
is assumed that the woodland and grassland lost is a
habitat of principal importance. Vegetation
clearance could therefore result in an adverse effect
on site integrity that is significant at the
district/borough level.
1.1.5
Dew’s Dell Site of Biological Importance lies partly
within land required for the construction of the
Proposed Scheme. Construction will result in the loss
of approximately 1ha (11%) of the site, which will
result in a permanent adverse effect on the integrity
of site that is significant at the district/borough level.
The Scheme will disturb two locations where
coralroot (Nationally Scare) has
been recorded;
effects that are assessed as significant at the county/
metropolitan level.
The Scheme will disturb two locations used by