Clean-up techniques for rocks and other hard surfaces
HP
hot water washing (datasheet)
Final clean-up of hard surfaces can be carried out using
a thermal pressure washer (20 to 150 bars, temperature of
0° to 90°). Even if the values displayed on the
thermometer and the manometer may not be entirely representative
of the output (due to a reduction in pressure and temperature),
the destructive effect of these machines can be high enough
to damage the physical and biological environment (burning
vegetation or sterilising surfaces for instance). It is
therefore important not only to seek optimum settings to
ensure a reasonable compromise between efficiency and impact,
but also to only clean what is necessary and to follow any
specific instructions which may be given for ecologically
sensitive sites.
The pressure washers used should be able to function with
seawater as it is more economical and ecological than using
fresh water and avoids the implementation of imposing logistics
which would be required for a fresh water supply. The washers
must also be easy to use and to transport. Furthermore,
urgent maintenance and repair of this type of equipment
requires maintenance to be carried out on site.
On large-scale pollution, it is advisable to concentrate
the machines rather than spread them out in order to ensure
a better maintenance and repair service as well as more
efficient cleaning.
This
type of cleaning should be preceded by the removal of large
accumulations of pollutant, as well as the installation
of protective measures for non-contaminated surfaces and
recovery of effluents.
Difficult
access sites (datasheet)
When response in cliffy areas is deemed necessary, certain
specific measures should be taken in terms of the equipment
needed, but also the personnel to be hired. Supplying human
and material means to the foot of a cliff requires, like
the evacuation of waste from a creek, the intervention of
highly qualified professional climbers who are the only
people able to set up the specialised installations (Tyrolean
traverse, life line and all the site’s safety installations).
Washing
agents
The purpose of using washing agents is to soften and remove
oil more easily from the rocks, which does not prevent prior
scraping of thick outer layers, nor hot water pressure washing.
The experience of the Erika and Prestige spills showed that
the use of such agents is not always necessary, even on
weathered heavy fuel oil. Nevertheless, the advantage of
washing agents on other pollutants can be assessed.
Washing agents can be divided into two categories:
- Solvents, or oil fractions (low aromatic content recommended < 5%), which remove oil from a surface, without dispersing it and allowing recovery of the removed oil
- Agents containing a solvent phase and a surface active phase: the surface active phase has an emulsifying effect, i.e. it disperses the removed oil and facilitates its penetration into the sediment. Due to the noxious effects of dispersed oil on flora and fauna, the use of products containing surface active agents should be exceptional, highly restricted, or even prohibited, in the presence of sensitive marine resources.
Whatever the type of agent selected, it should have undergone
prior testing (conducted by accredited organisations) on
its toxicity, biodegradability and efficiency. Cedre keeps
an up-to-date list of products which can be used on the
shoreline. Furthermore, controlled tests should be carried
out in the field to confirm the efficiency of the selected
agent on the pollutant in question.
The optimal use of these products involves spraying them
on the polluted surface, 15 to 30 minutes before washing.
The solvent dosage should be around 1 volume of product
for 3 volumes of pollutant.
Dismantling riprap
Ripraps, installations designed to protect the shoreline
from erosion, constitute veritable oil traps. The difficulties
encountered when cleaning riprap mean that it may need to
be dismantled, at least partially, as this may be the only
way to remove all the trapped oil.