INTRO | HIGHLIGHTS | FEATURES | INTERVIEWS | PERSPECTIVES
45
THE MAIN ENVIRONMENTAL IMPACT OF
ABANDONED COAL MINES ARISES FROM
THE ISSUE OF MINE WATER.
due to the escape of methane and
suffocation due to the emission of low
oxygen/high carbon dioxide mixtures.
Both of these risks are greatly increased
where gas is released into buildings
and other confined spaces. To address
these risks, vents have been installed
into workings known to be at risk of
containing gas at pressure, and these
are regularly monitored for any changes
in gas composition. In addition, two
active pumping schemes have been
installed in the North East to keep the
workings at sub-atmospheric pressure
to protect properties at risk. There is
also a specialised response to potential
gas-related hazards through the 24/7
hazard line.
ENVIRONMENTAL
IMPACTS
The main environmental impact of
abandoned coal mines arises from the
issue of mine water. These mine waters
are typically laden with soluble iron
sulphate which on contact with oxygen
at the surface precipitates iron ochre.
The ochre will turn water bodies a very
distinctive red/orange colour and can
kill off flora and fauna in those streams
and ponds.
Under the European Water Framework
Directive (WFD), countries have an
obligation to bring the quality of their
water bodies to a ‘good’ status and
the Coal Authority works with the
Environment Agency, the Scottish
Environmental Protection Agency and
National Resources Wales to address
a list of sites that require treatment to
conform with the WFD. To this end it has
designed and built over 60 mine water
treatment schemes in England, Scotland
and Wales. The great majority of these
schemes are systems to collect the ochre
and reduce the effluent to acceptable
levels (1mg/L iron) before being released
into streams, rivers, and the sea.
The significant active treatment scheme
in Britain is the plant at Dawdon in the
north east of England which treats water
high in iron and salt, then discharges
the treated water into the North Sea.
The Dawdon plant is used to treat water
that is pumped from mine workings
below an aquifer serving the north east
region with drinking water. Pumping is
required to prevent the iron entering the
aquifer and potentially causing iron rich
waters to enter the public water supply.
These actions are contributing to
making significant progress towards the
UK’s compliance with the WFD, and
significantly improving the environment
in coalfield areas of Britain.
REMEDIATING
MINE WATERS
Waters from abandoned metal mines can
contain dangerous levels of toxic metals.
They typically do not contain high levels
of iron and therefore often appear clean
and even drinkable. But unlike water
from coal mines there is no single body
with responsibility for treating these
waters. As a result, the Department for
Environment, Food and Rural Affairs
(Defra) is funding the Coal Authority to
look at the feasibility of treating metal
mine waters, and building schemes
to control contamination from the
many metal mines around the country.
Two such schemes have already been
constructed – one an ironstone mine
water issue at Saltburn in Cleveland and
the other a zinc and lead mine water
issue in the Lake District.
Research and development projects are
under way to reduce the risks from mine
collapses and the environmental impacts
of mine waters. These include using
alternative materials for repairing ground
collapses, understanding ground failure
mechanisms, and using remote sensing
methods for inspecting mine entries.
Studies are also being conducted into
how to build mine water treatment
schemes where ground for construction
is limited, and new methods of treating
metal mine waters.
Assessing risk to the public and the
Coal Authority’s liabilities are informed
by the large body of mining information
that is held by the Coal Authority. Coal
mine abandonment plans have both
been digitised and stored in the Coal
Authority’s GIS system. As well as being
the source of mining reports, which
the Coal Authority produces for house
buyers, these records form the principal
information base of the Coal Authority
and are used for assessing liability and
areas of particular risk.
Importantly, these records are vital
for the role of the Coal Authority as a
statutory consultee for local authority
planning applications. They enable
the Coal Authority to identify risks to
development from mining so that such
risks can be properly assessed. Key
plans identifying the 15 per cent of
coal-mined areas that are at highest risk
from mine entries and shallow mining,
have been provided to all relevant local
authority planning departments to assist
in determining where past coal mining is
an issue that needs to be addressed.
Steven Kershaw is Head of Research and
Development for the Coal Authority. Contact:
[email protected]
Above: Morlais mine water treatment scheme in Wales with two settling lagoons. Ochre can clearly be seen in the lagoon to the right.
Below: This polluted stream discharged into the sea via a beach used by holidaymakers.