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Visitors to Birmingham’s city centre are presented with what looks like
a waterside success story. The International Convention Centre stands out
against a backdrop of expensive hotels, and wine bars that now line the
city’s canal system. But take a few steps closer to the water and the glossy
business image begins to tarnish. Lurking at the bottom of the canals are
two centuries of industrial pollutIon, an unwelcome legacy that is costIng
more than £800 000 to remove.

Birmingham City Council, BritIsh Waterways and the Department of the
Environment, who are providing funding for the project, hope to clean the
sediment from a 5-kilometre length of the canal system so that fish, plants
and wildlife can return to the canal-side redevelopment zone. It is a more
difficult task than it might at first seem: the metals-processing and engineering
industries which sprang up after the first canals arrived in 1772, used
the waterways as a sewer as well as a means of transport, leaving behind
a multitude of pollutants.

‘Often the effluent from metal processing was a combination of the metals
themselves and the mineral oils used as coolants and lubricants in the machinery,’
says Phil Crowcroft, of the environmental consultancy Aspinwall, which is
managing the project. This left sediments at the bottom of the Birmingham
canals containing a poisonous coclctail of arsenic, copper, nickel and zinc
as well as heavy metals such as lead, cadmium and chromium.

It was clear from the start that the water quality could not improve
until contaminated mud had been dredged from the canal and removed. The
problem was what to do with it. The standard approach to reclaiming polluted
land in Britain is to dump contaminated soil in the nearest licensed landfill
site. But this only moves the problem somewhere else, so Birmingham decided
to treat the sediment dredged from the canal in a plant built for the purpose
on the canal bank.

The canal project is using a technique called ‘soils washing’ which
is already proven in the Netherlands, where the law imposes much stricter
controls on soil pollutIon than apply in Britain. The process is a development
of techniques used in the minerals-processing industry to extract ores from
the bulk of mined or quarried rock. ‘In polluted soils, most of the chemical
contamination adheres to the surface of particles,’ explains Crowcroft.
Because small particles have a higher ratio of surface area to volume than
larger ones, most of the pollutants can be removed from the soil by separatIng
the smallest particles.

When mud from the canal arrives at the canalside plant the first stage
in the cleanup is to remove large pieces of debris, including the inevitable
supermarket trolleys and bicycles. Next the coarser fraction, containing
material more than 10 millimetres across, is separated by washing and screening.
A secondary screen removes particles of more than 5 millimetres. The remaining
material, which amounts to about half the original sediment, then passes
to a ‘hydrocyclone’ where centrifugal force separates silt containing particles
less than 63 micrometres across from the courser sand. The sand fraction
includes copper filings produced by generatIons of machinists, but is otherwise
only lightly polluted with metals and so is suitable for the construction
industry. The silt that remains amounts to around 30 per cent of the original
material. Each tonne of this silt contains 60 kilograms of heavy metals,
showing that the pollutants are concentrated in this fraction, which is
dumped at licensed sites in the area.

Britain does not have any legal limits on the concentration of toxic
material in soil dumped in landfills. And there is little control over industrial
pollution of land. In the Netherlands any land polluted beyond a level defined
by law-the Dutch C standard-must be cleaned up by the site’s owner. Of the
sediment samples taken from the bottom of Birmingham’s canals, 80 per cent
were polluted beyond the Dutch C standard.

Crowcroft concedes that the Dutch regulatory authorities would probably
require the silt produced by the soils washing process to be treated further
before it is dumped. One option is add washing to remove the remaining metals-a
process likely to double the total cost of treatment; incineration is another
possibility. Crowcroft says soils washing centres are now being developed
in the Netherlands, where soils from various sites are assessed and matched
so that each can be given appropriate treatment.

In Britain the government-run Warren Spring laboratory has been at the
forefront of research into the application of minerals processing techniques
to land reclamation. The laboratory, now threatened with closure (This Week,
22 May), has won contracts from the US Environmental protection Agency (EPA)
and the European Commission for contaminated land research.

In addition to gravity-based soils washing techniques, Warren Spring
is looking at froth flotation, a process which separates particles according
to their surface properties-in particular whether the particles are readily
suspended in water or repelled by it. Warren Spring is also investigating
magnetic separation techniques. In a process originally developed for extracting
high-value ores, a fine magnetic material such as magnetite is added to
the contaminated mixture. The magnetite is absorbed onto the surface of
contaminant partIcles, causing them to separate out when subjected to a
magnetIc field.

For some pollution problems a combinatIon of soil cleaning techniques
may offer the best solution. ‘If you combine treatments you can use the
strength of one to make up for the weakness of the other,’ says Paul Bardos,
who leads the research on land contamination at Warren Spring. This ‘treatment
train’ approach is emerging as the focus of much of the research effort
around the world. The principle is even gaining ground in the US, where
until recently incineration was the norm.

Picking up the tab

The US has tough pollution standards that stem from the Superfund legislation
of 1980, which makes landowners liable to civil action if their land has
a high level of contaminatIon, even if they did not cause the pollution.
In 1986 the fund was enlarged to $8.5 billion to cover litigation and emergency
cleanup projects that follow court action by the EPA. Last year alone the
US spent around $22 billion on cleaning up toxic waste sites, according
to estimates by the Hazardous Materials Control Resources Institute.

Much of this money went on incineration. Last summer, in a typical project,
105 trailers and a 100-tonne mobile crane descended on a chemicals waste
site in Kingsville, Ohio. The trailers carried a mobile incineration plant
that took two weeks to erect. By the end of this year the project leaders
intend to have dug up and crushed all the contaminated soil and fed it through
the plant. The advantage of this technique is that it avoids the need to
transport wastes by road.

But incineratIon projects are often controversial. In February this
year, a federal judge at Jacksonville, Arkansas, halted cleanup work on
a Superfund site after environmentalists questioned whether emissions from
this Dollars million incineration project met federal standards. The site
was contaminated with waste from a plant that manufactured herbicides, including
the Agent Orange used as a weapon by the US during the Vietnam War. The
focus of the environmentalists’ campaign was dioxin, the highly toxic chemical
produced when materials containing chlorine are incinerated.

‘There’s a great propensity in the US to be anti-incineration and that
causes us enormous problems,’ says Richard Nalesnik, physical science administrator
of the EPA’s Superfund Innovative Technologies EvaluatIon (SITE) programme.
‘The NIMBY not in my backyard syndrome has prevented us from putting up
new incinerators.’ Launched in 1986, SITE publicises alternative technologies.
So far it has completed 43 projects and a further 100 are under way. ‘SITE
is beginning to reveal the options that are available,’ says Nalesnik.

At McClellan air-force base, near Sacramento in California, SITE runs
a project, jointly funded by the EPA, the US Air Force and chemicals companies,
to test methods of dealing with heavy contaminatIon by organic chemicals,
in this case aviation fuel. The conventional technique for managing such
pollution is to pump the groundwater and clean it, but this cannot remove
the vapour from the soil above the groundwater so it recontaminates the
water.

AlternatIve technologies include vacuum extraction, where hydrocarbon
vapour is pumped out of the polluted soil and burnt or passed through a
ventilation system, and bioremediation, in which soils are aerated to encourage
the growth of bacteria that will feed on the pollutants. Two methods can
complement each other. On one air force project using vacuum exraction,
pollutant levels were found to be dropping faster than expected. The effect
was attributed to biological decomposition triggered by aeration: as the
vapour was extracted, air moved into the space it once filled.

The observation led to the development of ‘bioventing’, which combines
vacuum extraction with bioremediation. Air pumped into wells penetratIng
below the water table bubbles up through the groundwater, promoting decompositIon
of the pollutants. The bioremediation process is also an effective way of
treating the soil just above the water table. It can be optimised by controlling
the rate at which air is injected and vapours extracted. ‘The system has
been successfully used on approximately 60 petrol statIon sites, leaving
groundwaters typically cleaned to drinking water quality,’ says Ian Mugglestone
of the US-based consultancy Brown & Root Environmental.

Like the treatment train approach favoured by Warren Spring, bioventing
harnesses two land remediation processes in tandem. This idea of using a
combination of different techniques has attracted attention from the Committee
for Challenges to Modern Society, a NATO body which aims to encourage researchers
from different countries to share their results. One of the projects being
promoted by the NATO initiative is a chemical process for removing heavy
metals from wood treatment sites. Developed by Davy International of Stockton-on-Tees
in Cleveland, the technique has won research funding from the British and
Danish governments, and has been accepted for evaluation under the American
SITE programme.

The Davy process, like the soils washing technology used on the sediments
from Birmingham’s canals, splits soils into coarse and fine fractions. But
the Davy process goes further than the Birmingham operation and recovers
heavy metals from the silt fraction using adaptations of minerals processing
techniques. In one process, normally used to extract uranium from its ore,
an ion-exchange resin is mixed with the soil to form a pulp. A variation
on this process, originally developed to extract gold and silver, uses activated
carbon. The contaminants are absorbed by the resins or the carbon, which
is then extracted from the mixture, cleaned and recycled. British Nuclear
Fuels is participating in the NATO programme with a patented chemical process
originally developed for treating nuclear wastes.

A great deal of research on land remediation-particularly in the fields
of soil separatIon and bioremediation-is done in Britain, but the technologies
are rarely used on British soils. ‘Very little land remediation takes place
in the UK as yet,’ Mugglestone confirms. But, having recently opened a British
office, his company is confident that demand will materialise. Britain is
thought to have 100 000 contaminated sites.

In 1990, the British government introduced legislation for a register
of potentially polluted sites. But earlier this year, plans for the register
were withdrawn amid fears that too much land would be blighted if it was
thought to be polluted. British law does give the National Rivers Authority
and local authorities the power to demand a site to be cleaned up if there
is evidence of severe groundwater pollution, but this has yet to be enforced.

But despite the lack of effective legislatIon, and the uncertain future
of research into soil cleaning technologies, Bardos of Warren Spring remains
upbeat about future developments in the technology of land remediation.
‘Many of the answers to contaminated land problems are still unknown-and
UK teams are doing some good work,’ he says. ‘The contaminated land genie
is out of its bottle, and try as they might no one will be able to shove
it back in.’