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BOC Immingham Dissolved Acetylene Project Environmental Statement: Vol. 2 Main Text
18.17 The assessment concluded that the planned design, management and control of the Dissolved
Acetylene Project in relation to surface water quality are sufficient; thus no specific mitigation
measures have been identified. The CEMP will include a method statement detailing the proposed
techniques for ensuring that the water quality of Middle Drain and the Humber Estuary will be
protected. As a result of the assessment it has been recommended that this is submitted and
agreed with NELC prior to commencement of development.
Flood Risk
18.18 The assessment of flood risk has considered the following sources of flooding: tidal, fluvial (Middle
Drain), groundwater, pluvial surface water and sewer. There are no sewers in the area and there
is no knowledge of flooding to the proposed development site to date from all potential identified
sources. The risks of flooding to and from the site are considered to be similar for both the
construction and operational phases (albeit that the construction period is such that there is no
requirement to account for climate change.
18.19 The site is currently protected to at least a 1 in 1,000 year tidal event by coastal defences. The
site has a residual risk from overtopping of the defences during more extreme tidal events (above
0.1% AEP) and from a breach of the coastal defences. The risk from the breach of the coastal
defences will be managed by providing a flood warning system; safe evacuation routes; and
evacuation procedures. During operation, safe refuges will be provided above the breach water
level within the Generator Building and secondary flood protection to electrical equipment will be
provided through water tight doors. On this basis the tidal flood risk is considered to be negligible.
18.20 There is a risk of flooding from Middle Drain in the event of failure of the pumping station.
However, the station operates with duty and standby pumps and overall the risk is considered to
be minor.
18.21 The site is at moderate to high risk of flooding from groundwater but the main influence on
groundwater levels within the development site will be the tidal levels. The measures incorporated
into the design of the site to manage the tidal and surface water flood risk are suitable for
managing the groundwater flood risk such that the significance of the impact is considered
negligible.
18.22 There is an increase in compacted soils and or impermeable areas associated with the proposed
development, and, therefore an increase in surface water runoff. As part of the CEMP, surface
water runoff during construction will be managed such that it will not increase the risk of flooding
at the proposed development site, or to land within the surrounding area during construction.
During operation, surface water runoff will be managed through an appropriately designed surface
water drainage system and pumping station which outfalls into Middle Drain. The site is
considered to be at minor risk of flooding from pluvial surface water during construction and
negligible risk of pluvial surface water flooding during operation.
18.23 The assessment concluded that the planned design, management and control of the Dissolved
Acetylene Project in relation to flood risk are sufficient; thus no specific mitigation measures have
been identified. Nonetheless, the following recommendations have been made:
� BOC should continue to liaise with the EA to ensure they are informed of any changes to the
standard of protection provided by the coastal defences and any changes to the flood
warning system; and
� BOC should continue to liaise with NELDB to ensure they are informed of any changes to the
standard of protection provided by the pumping station on Middle Drain.
5100935.404 Environmental Statement August 2011 301