Memorandum submitted on behalf of Brunner
Mond, British Salt and Ineos-Chlor
1. INTRODUCTION
AND SUMMARY
1.1 This paper is presented on behalf of
Brunner Mond, Ineos-Chlor and British Salt, whose business undertakings
involve the disposal of inorganic process residues from soda ash
manufacture or brine purification into deep underground brine
cavities. The companies are concerned about the potential impact
of future environmental regulation on this sustainable and environmentally
beneficial waste management activity and therefore wish to submit
evidence to the Committee to illustrate the benefits of brine
cavity disposal as an innovative waste management option.
1.2 Many industrial and domestic activities
produce waste by loss of raw materials, contamination of intermediates
and products, unwanted packaging materials, the inefficient use
of raw materials and energy etc. We commend the principles of
the waste hierarchy when applied to this type of waste and appreciate
the need to move up the chain particularly to minimise the need
for landfill. However there are a number of inorganic processes
where the so called "wastes" are unavoidable arisings
due to the use of naturally occurring raw materials such as salt,
limestone, coal and other minerals. Much as these industries would
love to have secondary uses for these unavoidable residues and
will no doubt continue to look for such uses, the reality is that
no such uses have been discovered; their generation is unavoidable;
and landfill or total dispersion to the natural environment are
the only available options. Attempts to eliminate or reduce these
types of waste would lead to a pro-rata reduction in the national
output of such products as soda ash, sodium bicarbonate, chlorine,
purified salt etc and the consequential import of these materials
and their derivatives from producers overseas if modern living
standards are to be maintained. (This includes many materials
that are essential for everyday life such as glass, detergents,
pharmaceutical products associated with kidney dialysis etc.)
1.3 The controlled use of brine cavities
for the deposition of solid wastes in a saturated brine carrier
represents not only a long term, safe and highly reliable method
of waste deposition which has been used since the 1950s, but is
also the best application of BEO (best environmental option) you
could find for the relevant waste materials. This has now been
accepted by senior officials at DEFRA and the Environment Agency.
Future regulations in the UK should acknowledge the benefits of
this activity. If it were rendered uneconomic, alternative technologies
would result in the excessive use of surface landfill, enormous
amounts of energy to separate and dry the waste to avoid it being
in liquid form, or the use of huge amounts of other chemicals
to treat the waste. None of these could be justified as sustainable
options.
2. USE OF
BRINE CAVITIES
2.1 In the UK some wastes are currently
disposed of to "brine cavities" full of saturated brine
created by the solution extraction of salt from deep underground
salt strata. Solid wastes from brine purification and soda ash
production are pumped into the cavities by pipeline, using saturated
brine as a carrier.
2.2 Brine cavities are generated during
the extraction of saturated sodium chloride brine by a process
of solution extraction. After drilling of the initial shaft (450mm
diameter), which is lined to avoid any contact with surface and
sub-surface geology, water is pumped to the target area to start
the cavity formation. The cavity is usually developed over a period
of five to 10 years to its full working capacity. The overall
life depends upon rates of extraction of the saturated brine but
when fully worked the cavity is a pear shaped void of approximately
one to two million cubic metres filled with saturated brine. During
the life of the cavity, while salt extraction is being carried
out, it is regularly monitored by specially developed sonar techniques
for shape and size, both of which can be controlled using a system
of "air blanketing". The salt deposits are typically
200m thick overlain by 200m of boulder clay. Each cavity is a
mechanically stable structure, and represents an independent cell
and is not normally in any way connected to any of the adjacent
cells.
2.3 An example of their structural stability
and impermeability is the use of brine cavities for strategic
storage of natural gas and ethylene.
2.4 When a brine cavity is fully worked
out it is potentially available for the deposition of certain
wastes. In particular, they are currently used for the deposition
of residues derived from the purification of raw brine and the
production of soda ash using the Solvay ammonia soda process.
The wastes from the ammonia soda process undertaken by Brunner
Mond are solids derived from impurities in brine, limestone and
coke and a certain amount of calcium sulphate from the reaction
of calcium ions from burnt limestone reacting with sulphate in
the incoming brine. Other materials incorporated are silicates
precipitated as inert calcium silicate, water purification solids
(calcium carbonates and spent zeolites) together with sand and
silt settled from incoming water and fine limestone.
2.5 These wastes are virtually insoluble
in the saturated brine into which they are settled, with the brine
acting as a carrier to transport the solids by pipeline to the
cavities. Once in place the solids settle in the cavity together
with the naturally occurring clay minerals already present in
the cavity to form a stable inert mass. The solids are insoluble
in the saturated brine and are totally unreactive within the cavity
environment.
2.6 The waste materials derived from brine
purification undertaken by British Salt and Ineos-Chlor are inorganic
salts precipitated from crude brine during the purification process
together with small amounts of clay minerals which settle out
of the crude brine, but originate from the natural salt deposit.
These precipitates are essentially calcium carbonate and magnesium
hydroxide, which are inert in relation to the cavity environment,
and these settle in the cavity.
2.7 Separate cavities are used to deposit
approximately 80,000 tonnes of ammonia soda waste each year and
approximately 98,000 tonnes of brine purification solids, thereby
maintaining the individual cell concept.
2.8 Disposal in a brine cavity brings benefits
as the salt is impermeable and "creeps" such that it
is self-healing. The stresses within the salt beds as a result
of solution extraction are well within the elastic limits of the
salt and plastic deformation or other modes of failure will not
occur due to the inherent qualities of the rock salt strata. Dissolution
of the salt affecting the stability of the cavity does not occur
as the cavities are created in rock strata unaffected by water.
2.9 Historically, wastes of various types
have been disposed of in coal mine shafts. Elsewhere, wastes have
been disposed of by deep injection under pressure. There is one
facility in the UK for hazardous waste disposal in a "dry
salt mine".
2.10 The differences between "brine
cavities" and "dry salt mines" are fundamental
and it is important not to confuse the waste management benefits
and opportunities that each may present.
3. DIFFERENT
TYPES OF
UNDERGROUND DISPOSAL
3.1 It may be helpful to categorise the
four categories of underground disposal that can be undertaken:
1. Solution brine cavities. As described
above these are independent cells, in water soluble strata eg
sodium or potassium chloride. They are geologically isolated from
other strata, from groundwater and aquifers. They are usually
filled with saturated brine where the liquid is in equilibrium
with the soluble strata.
2. Dry mines from which minerals have
been abstracted. The deposits may be either insoluble eg coal,
iron, ore lead or copper ores, and wet or soluble eg salt, potash.
These may or may not be isolated from groundwater, they are usually
extensive underground structures or voids, and their condition
is determined by the type of extraction used.
3. Flooded mines. These are usually
"dry" mines, which on abandonment have been allowed
to flood by the penetration of groundwater for formation water
or possibly by deliberate water pumping to "stabilise"
the structure.
4. Deep high-pressure injection. This
is where the underground cavity is the interstitial space between
individual particles that make up the rock formation or fault
lines cracks and layers within the rock. The space is normally
filled with water (formation water) and this is displaced by injection.
Injection usually takes place using a fluid carrier for the solid
material.
3.2 The industry group comprising Brunner
Mond, British Salt and Ineos-Chlor who use brine cavities, wishes
to make it clear that salt cavities are used throughout the world,
including Europe, for the strategic storage of a range of materials
such as methane/natural gas, ethylene, propane, petrol, aviation
fuel, crude oil and other hydrocarbon storage. Whilst some of
these materials are stored as normal operational reserves of raw
materials, other national strategic stocks may be held for many
years. Each is subject to an appropriate risk assessment and licensing
regime but the method used is widely accepted as good practice
due to the long-term geological and structural stability of underground
brine cavities. The use of similar geological cavities for waste
storage throughout Europe and the US is quite extensive.
3.3 Although the Landfill Directive prohibits
the deposit of liquid waste into surface or underground landfill,
it does not preclude the use of liquid, such as brine, as a carrier
to facilitate emplacement of solids, into a brine cavity.
4. INTERACTION
WITH BRINE
AND THE
SURROUNDING ROCK
SALT
There is no adverse reaction with brine arising
from the current use of brine cavities for the disposal of inorganic
solid deposits by liquid placement using a brine carrier. All
deposits are settled into saturated brine prior to deposition
and are inert in relation to both the saturated brine and the
solid salt of the surrounding structure. There is therefore no
interaction between the deposited solids and the brine.
5. INTERACTION
WITH WATER
5.1 As the brine cavities are created by
injection of water it is important to avoid addition of water
to a cavity in a waste stream. The cavities must be created in
rock strata unaffected by external water ingress. This is the
situation for the brine cavities currently used for waste disposal
in the UK.
5.2 Biodegradability is not an issue with
disposal of inert inorganic solids to saturated brine cavities
as there is no organic content of the deposited solids or the
saturated brine. Brine is essentially 70% water and is totally
un-reactive with the deposited solids. The cavities are engineered
to be geologically stable and as far as is reasonably practicable
totally isolated from ground water, formation water or underground
aquifers.
6. INTERACTION
BETWEEN WASTES
6.1 In certain situations solid waste disposal
can cause effects such as gas generation (particularly biodegradation
of sulphates to form hydrogen sulphide), temperature and pressure
rise, and appropriate design would be required. These risks do
not occur with the current use of brine cavities for the disposal
of inorganic solid deposits by liquid placement in a brine carrier.
The wastes currently associated with brine cavity deposition are
un-reactive with themselves or with the environment within the
cavity. There is no perceived risk of any reaction gases being
produced or any impact on the cavity infrastructure. As is already
noted the salt deposits are said to creep and be "self healing",
presenting an impermeable environment. General strata fractures
are generally not believed to be of any significance or risk.
Due to the absence of any risk of gas evolution from current disposal
activities involving brine cavities, structural fractures are
unlikely to be caused from within the cavity.
6.2 Although these risks could occur if
biodegradable or hazardous wastes were disposed of to brine cavities
or dry salt mines, such activity may still be permitted if a risk
assessment of each scheme concludes that the risk is acceptably
low and that the substances for disposal are not prohibited by
the EU Landfill Directive.
7. RELEASES TO
THE ENVIRONMENT
In dry salt mines releases to the environment
could take place due to a management failure allowing water into
the cavity. This would not occur in the case of brine cavities
because by the time they are being used for waste disposal all
water supplies have been fully disconnected and are remote from
the location of the cavities which are otherwise sealed from surface
activities. Release could occur in geological time in the case
of both brine cavities and dry salt mines due to crustal movements
and erosion but the risk is regarded by regulatory authorities
as minimal. Salt strata are considered extremely stable, hence
the use of brine cavities for underground storage of natural gas
and other products in the UK and many other parts of the world.
There is no evidence of any such releases into the environment
from brine cavities in the UK since their use for waste disposal
begun in the 1950s.
8. RISK OF
FIRES
Where dry storage takes place, there could be
a risk of fire if organic materials are stored. This would not
be the case in deep sealed brine cavities where brine, which is
always present, precludes oxygen without which a fire would be
impossible.
9. CONCLUSIONS
9.1 Cheshire County Council, DEFRA and the
Environment Agency recognize that brine cavity disposal is a safe
and sustainable waste management option. Wastes for disposal in
underground brine cavities can therefore be inert waste or non-hazardous
non-biodegradable waste disposed of in saturated brine solution,
with the use of brine as a carrier. Except in the case of inert
waste this would be subject to a specific risk assessment to determine
whether there might be any unacceptable level of risk of environmental
pollution.
9.2 It is important that the Government
accepts that the established waste hierarchy is not, and should
not by regarded as, a fixed and rigid system, but must allow for
exceptional cases.
9.3 For the reasons given above and in view
of its long term environmental benefits, the use of brine cavities
for waste disposal should, despite being classed as landfill,
be seen as a desirable form of waste management in appropriate
circumstances and should be regarded as an exception to the waste
hierarchy. Brine cavity disposal is operated under techniques
that have been developed for almost 50 years but should now be
considered as an environmentally beneficial and innovative waste
management solution for the present and future.
Brunner Mond,
ICI Chlor-Chemicals and British Salt
7 January 2003
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