Survey – essential that a geo-technical survey is undertaken to determine
whether contaminants are in the soil and ground water. Of particular concern are: acids, heavy metals, salts,
cyanides and coal tars, in addition to organic material which decompose to form
the highly explosive gas (methane).
measures for subsoil containing chemicals or other contaminants are varied.
traditional low-technology method for dealing with contaminated sites has been
to excavate the soil and remove it to places licensed for disposing. With the
increase in building work on brown-field sites, suitable dump are become scarce
resource. labour-intensive operations with large volumes of this type of waste
leads to high costs. Also, where excavations exceed depth of about 5 M, it
becomes less practical and too expensive. Alternative physical, biological or
chemical methods of soil treatment may be considered.
excavation – used to remove fuels or industrial solvents and other organic
deposits. At variable depths, small diameter boreholes are located at frequent
intervals. Attached to this are vacuum pipes to draw air through the
contaminated soil. The contaminants are collected at a vapour treatment
processing plant on the surface, treated and evaporated into the atmosphere.
This is a slow process and it may take several months to cleanse a site.
– use of low voltage in the presence of metals. Electrolysis flows between
anode and cathode, where metal ions in water accumulate in a sump before
pumping to the surface for treatment.
– sub-soil boreholes are used for the pumped distribution of liquid hydrogen
peroxide or potassium permanganate. Chemical and fuel deposits convert to water
and carbon dioxide.
extraction – the sub-soil is excavated and mixed with a solvent to break down
oils, grease and chemicals that do not dissolve in water.
– the removal of contaminants by plants which will absorb harmful chemicals
from the ground. The plans are subsequently harvested and destroyed. A variant
uses fungal degradation of the contaminants.
– stimulating the growth of naturally occurring microbes. Microbes consume
petrochemicals and oils, converting them to water and carbon dioxide.
Conditions must be right, a temperature of at least 10C with an adequate supply
of nutrients and oxygen. Untreated soil can be excavated and placed over
perforated piping, threw which air is pumped to enhance the process prior to
the soil being replaced.