SHEQWs Newsletter November

Incident - Chalk/Calcium Carbonate
Discharge to a Non-Main River
What happened?
• A recent incident on an eight2O
site saw chalky water discharged
into a non-main river (usually
a dry ditch) situated parallel to
the site. The site had set up the
dewatering system three weeks
previously, had a permit to pump
formalising their monitoring
regime and had undertaken the
activity without any problems
until the morning of the incident.
• Following a complaint received
downstream of the site, the
discharge point was checked and
cloudy water was observed being
released into the environment.
At this point all pumping and
dewatering activities were
immediately stopped.
Why did it happen?
There are 2 potential reasons for
the incident which may have acted
individually or in combination:
• The blinding activity undertaken
on the day of the incident may
have impacted on the alkalinity
of the water in the vicinity of the
shaft. A change in alkalinity can
turn water containing calcium
carbonate cloudy. This water was
then drawn up by the dewatering
sump and into the silt trap.
• A change to a more chalk like
ground strata meant that the
equipment being used was
no longer appropriate for the
dewatering activity.
What were the potential
consequences of this
incident?
Water contaminated with suspended
solids such as chalk can be extremely
damaging if allowed to enter
watercourses. Damage can include:-
• Blocking fish gills leading to
death
• Deoxygenating water killing any
reliant organism
• Smothering aquatic plants
• Transport of toxins into an
ecosystem
• Alteration of a rivers chemistry
e.g. pH which can have an impact
on certain species
• Water pollution events such
as this account for many
prosecutions under the Water
Resources Act each year and can
result in unlimited fines and even
prison sentences. Prosecutions
can also have a significant impact
on the reputation of our business
and can also impact on future
work winning.
What can we do to prevent it from happening again?
• Where dewatering to surface water, a watercourse precondition checklist must be completed and the site
must ensure that the wider environment is assessed within this (i.e. flowrates of the watercourse prior to
discharge, water quality samples from both up and downstream and photographs of all monitoring locations)
• All dewatering operations must be fully risk assessed using the necessary templates
• Ensure that the site has established what water and potential sediment will need to be monitored in terms of
quantity, quality etc.
• Changes in the environment , including a variation of ground strata, should lead to a reassessment of the risk
• Dewatering operations require the use of the eight2O Permit to Pump process to be followed.
• Dewatering and pumping operations must be appropriately monitored with records kept including
photographic evidence of all samples taken.
• IEMP control plans must be site specific to the activity being undertaken and identify water management
equipment specification, monitoring and maintenance requirements etc.. Relevant activity specific
information such as monitoring should also be included within the RAMS.
• When dewatering to surface water, monitoring must be undertaken at locations downstream as well as at the
initial discharge point.
Page 6 | November 2016 SHEW Newsletter
SHEW Newsletter
November 2016 | Page 7