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Prevention of these
forms of transmigration can be achieved using simple,
common sense systems:
1) Airborne Fibre release- using a water bowser and
fine spray nozzle, a mist of water or water pva mix
can be drifted over the material during excavation,
lifting and deposition on the wagon or dumper (this
is a fine balance between over-weighting the material
effecting tipping costs and dust suppression. Some training
and experience will be required by the site operative
involved but this takes a fairly short time to perfect.
See photographs for this system in action at Paradise
Tip, Witton Park, an 8 month long contract for One Northeast.
A mist spray or spray
curtain can also be employed to down any airborne dust
which positioned correctly. Any haul roads or areas
of the site where contaminated machines are like to
raise dust must be sprayed with a bowser to prevent
any visible dust release. Airborne dust blowing across
site is the most likely source of complaints from members
of the public- they cannot tell whether it is asbestos
or not so its suppression must be regarded as essential.
To measure the effectiveness
of these measures, the site analyst carries out continual
long-term background monitoring at established sampling
points on the site’s perimeter fence and personal
monitoring on himself, plant operatives and any banksmen
/ spray operators.
2) Cross-migration- Control is achieved by fencing the
site into Dirty (contaminated and work area) and Clean
(parking, office and public access) areas and directing
all access and egress between the two via a decontamination
unit (people) and Wheel-washing facility (vehicles).
A specialised metal trough with numerous nozzles to
either side can be acquired for wagons to drive through
and have wheels and bodies washed off as they pass through
it. All site machinery (excavators, dumper trucks etc.
remain on the Dirty side of the site until all work
is completed. They are then power washed, allowed to
drive and then swab tested and have reassurance air
testing in their cabs prior to being allowed off site.
All site personnel must
wear disposable PPE and suitable P2 or P3 RPE depending
on the material being excavated. It is possible to acquire
nylon overalls that can be re-used and sent to a specialist
laundry for long-term jobs where the cost of disposables
will become prohibitive. Regular reassurance air monitoring
should be undertaken by the site analyst in the DCU’s
clean end to ensure the system is working.
To prevent the work
site itself becoming cross-contaminated by vehicles
carrying asbestos waste as parts become completed, it
is common practice to commence excavation down to clean
at the farthest end of the site from the Clean area
and work gradually back towards the entry / exit point-
vehicles travel only over ‘dirty’ material.
Otherwise, haul roads will need to be constructed from
hard-core fill either from material crushed on-site
or brought in at cost from elsewhere.
Waste Issues
Transport of contaminated / special waste could prove
extremely costly and where possible (with the consent
of the client and the environment agency) retaining
the waste on site (for example inside bunds or banks
or under roads) should be investigated as the best environmental
option. Remember that the waste will only end up underground
anyway and if you can save the damage to the environment
by transportation of the material by road as well as
the cost of haulage and tipping, then this should be
pursued. At the Seaham remediation site MIS saw the
installation of contaminated waste beneath new roads
being constructed and at Marske in Cleveland asbestos
cement was used in the centre of newly constructed earthwork
bunds. In all cases, the material must be capped (preferably
with clay and some form of high visibility membrane
to warn anyone potentially excavating in future) with
at least 500mm of neutral material. The position of
the waste along with depth and quantity must be carefully
documented and the records retained indefinitely by
the site owners.
Where waste must be
taken off site (and with Special Waste this is usually
the case) wagons must be covered (most have a removable
cover anyway) and pressure washed after use. They can
then be swab tested and verified as clean before commencing
other work. The wagon can be sheeted out with polythene
to prevent contamination if this is deemed practical
based on the material being transported. Whilst on site
and at the landfill, wagon drivers must keep windows
close and where a disposable mask. Regular personal
and reassurance air monitoring should be carried out
in random wagons by the site analyst.
Remediation Analyst’s Process In A Nutshell
· Establish asbestos
presence (trial pits and sampling)
· Draw up a specification
and site plan
· Fence off site (warning
signs) and designate clean and dirty areas
· Install DCU and wheel-wash
across the barrier between clean and dirty
· Suppress dust release
while excavating material.
· Visible dust or winds
>20 knots stop work until problem subsides
· Visually identify the
type of waste and treat accordingly
· Waste off site via wheel-wash
with appropriate documentation
· Excavation works from the back
of the site towards the wheel-wash leaving clean material
behind
· All machinery jet-washed
and tested prior to leaving site
· Final sampling to establish
site cleanliness
· Leave site
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