SiteSurvey – essential that a geo-technical survey is undertaken to determinewhether 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 formthe highly explosive gas (methane).Remedialmeasures for subsoil containing chemicals or other contaminants are varied.Thetraditional low-technology method for dealing with contaminated sites has beento excavate the soil and remove it to places licensed for disposing.
With theincrease in building work on brown-field sites, suitable dump are become scarceresource. labour-intensive operations with large volumes of this type of wasteleads to high costs. Also, where excavations exceed depth of about 5 M, itbecomes less practical and too expensive.
Alternative physical, biological orchemical methods of soil treatment may be considered.Vapourexcavation – used to remove fuels or industrial solvents and other organicdeposits. At variable depths, small diameter boreholes are located at frequentintervals. Attached to this are vacuum pipes to draw air through thecontaminated soil. The contaminants are collected at a vapour treatmentprocessing 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.
Electrolysis– use of low voltage in the presence of metals. Electrolysis flows betweenanode and cathode, where metal ions in water accumulate in a sump beforepumping to the surface for treatment.CHEMICAL:Oxidation– sub-soil boreholes are used for the pumped distribution of liquid hydrogenperoxide or potassium permanganate. Chemical and fuel deposits convert to waterand carbon dioxide.Solventextraction – the sub-soil is excavated and mixed with a solvent to break downoils, grease and chemicals that do not dissolve in water.BIOLOGICAL:Phytoremediation– the removal of contaminants by plants which will absorb harmful chemicalsfrom the ground.
The plans are subsequently harvested and destroyed. A variantuses fungal degradation of the contaminants.Bioremediation– stimulating the growth of naturally occurring microbes. Microbes consumepetrochemicals and oils, converting them to water and carbon dioxide.Conditions must be right, a temperature of at least 10C with an adequate supplyof nutrients and oxygen. Untreated soil can be excavated and placed overperforated piping, threw which air is pumped to enhance the process prior tothe soil being replaced.