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BOC Immingham Dissolved Acetylene Project Environmental Statement: Vol. 2 Main Text
3.55 There will be no flooding (on site or offsite) from the drainage system during a 1 in 30 year storm.
Any flooding during longer return period storms (up to the 1 in 100 year storm with 30% allowance
for climate change) will be contained within the site. Any on site flooding (caused by storms with
return periods longer than 30 years) would be allowed to flood the paved surfaces in a controlled
manner such that water is shed away from buildings and would either be stored locally (to return
to the drainage system when the storm abates), or be allowed to flow through the site towards the
outfall and routed to avoid buildings. The system will be designed in such a way as to prevent
flooding of adjacent agricultural land up to the 100 year return period storm (with 30% allowance
for climate change) and for storms of longer return period if it is practicable to do so.
3.56 The drainage network incorporates an oily water separator (OWS) to reduce hydrocarbon pollution
and catch pits to capture silt particles. The clean rainwater from the Drainage System will
discharge to Middle Drain via a pumping station. The pumping station will contain three pumps
with variable speed drives capable of discharging to Middle Drain at flow rates between 25 l/s and
300 l/s. Flows in excess of 300 l/s will overflow into the Deluge Lagoon and ultimately be returned
to the pumping station via a low level return.
3.57 The area beneath the Lime Storage Tanks will be at a lower elevation than the rest of the site and
will have a valved connection to the Drainage System. The valve will be controlled locally. Under
normal circumstances the valve will be open but when loading is taking place the valve will be
automatically closed to prevent any spillages from entering the Drainage System and to enable
containment of any spillages. Any rainwater runoff from the Carbide Turnbin Storage Areas will be
diverted to the area below the Lime Storage Tanks.
3.58 Any rainwater runoff from the Designated Area for Solid Waste (where the unreacted carbide coke
waste will be stored) will be diverted to the Lime Sump.
3.59 The following areas will be bunded (to 110% of the capacity of the largest tank):
� Acid and Lye Store vi ;
� Acetone Tank;
� Lime Sump; and
� Waste Liquor Tanks.
3.60 Clean rainwater that collects in the bunds will, after inspection to confirm quality, be pumped from
the bund and into the Drainage System. Any spills, or contaminated rainwater, will collect in the
bund prior to removal for disposal offsite. The bunds will not connect directly to the surface water
drainage system.
Domestic Waste Water
3.61 Domestic waste water will be generated from the staff facilities in the Amenity Building. As there is
no foul sewer in the vicinity of the proposed site, domestic waste water will be treated on site in a
rotating biological contactor (RBC) type treatment plant. The treatment plant will be located close
to the Deluge Lagoon.
3.62 Depending on the level of treatment required, the RBC may be supplemented with a reed bed.
The treated effluent would be discharge to Middle Drain via the Site Drainage System. For an
average workforce of 17, peak flows are expected to be less than 0.5 l/s. Middle Drain already
receives treated domestic waste water from other facilities, including the existing BOC site. The
discharge will require consent.
vi
Lye is another name for sodium hydroxide. Note, the Acid and Lye Storage Area will provide storage for other chemicals in addition to
sulphuric acid and sodium hydroxide (see Table 3.2).
5100935.404 Environmental Statement August 2011 24