8 REMEDIATION OPTIONS - Castings Technology International

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8. Remediation Options An overview of remediation options that have been applied in the UK is provided below. Table 32. A Classification of Some Remediation Options Applied in the UK <strong>Technology</strong> Class Application Medium Linkage Element Affected Excavation and off site disposal Civil Engineering Ex situ Soil, Free product, water, vapour Source management Pump and treat Physical Ex situ Free product, Water Source management Air sparging Physical In situ Water Source management Soil washing Physical Ex situ Soil Source management Soil vapour extraction Physical In situ Soil – vadose zone Source management Windrows Biological Ex situ Soil Source management Biopiles Biological Ex situ Soil Source management Thermal desorption Thermal Ex situ Soil Source management In situ vitrification Thermal In situ Soil Source management Incineration Thermal Ex situ Soil, free product Source management Capping Civil Engineering In situ Soil Pathway interruption Vertical barriers Civil Engineering In situ Free product, water, vapour Pathway interruption Bioslurping Biological In situ Water Pathway interruption Biosparging Biological In situ Water Pathway interruption In situ oxidation Chemical In situ Soil Pathway interruption In situ reduction Chemical In situ Soil Pathway interruption Monitored Natural Attenuation Biological, chemical & physical In situ natural processes Water Pathway interruption Permeable reactive barriers (PRB) are a means of bringing some of the advantages of ex situ technologies to the in situ domain. They comprise an impermeable barrier (the ‘funnel’) with an opening (the ‘gate’) that allows contaminated water or vapour to flow through. PRBs operate by allowing or funnelling contaminated water or vapours to reach the gate and then treating the contamination while allowing the carrier water or soil air to pass freely through the barrier. Page 92
8. Remediation Options 8.1 Source management Remediation targeted at the source of contamination can seek to remove the contaminants, destroy them, change their chemical form or immobilise them. 8.1.1 Soil Both heavy metals and organic contaminants can adhere to the soil particles, especially clay and vegetation components. In situ source management options for contamination in soil include: • solidification and stabilisation, • vitrification. Ex situ methods involve excavation of the contaminated soil or pumping contaminated water or vapour out of the ground followed by disposal or treatment. Technologies include: • off site disposal to licensed landfill site, • encapsulation in an on site engineered cell, • soil washing and then treatment or disposal of the contaminated residue. 8.1.2 Free product and non aqueous phase liquids Leaking tanks or spills can result in free product migrating down through the ground. Some products will dissolve readily in groundwater. Others are not soluble or only sparingly soluble in water – they are called non-aqueous phase liquids (NAPL). NAPL such as petrol or diesel are lighter than water and will float on the water table (LNAPL). Chlorinated solvents such as trichloroethene (TCE) are denser than water and will sink through the ground water to the bottom of an aquifer (DNAPL). In situ remediation options include monitored natural attenuation (MNA). Natural attenuation has been observed at the edges of many occurrences of free product. However degradation of the core of a source area is only very rarely possible. MNA is particularly effective for dissolved phase hydrocarbons and phenol (in low to moderate concentrations, but ineffective for dissolved chlorinated solvents. Once contamination has entered the fissures of bedrock it is almost impossible to remove it all. This makes it difficult to develop ex situ techniques for fractured bedrock. Ex situ methods include pumping free product and destroying, treating or disposing the recovered fluids. This can reduce the amount of free product remaining in the ground, but is a slow and expensive process with variable results. 8.1.3 Vapour/ gas In situ remediation options are limited, but include soil vapour extraction. Preventing infiltrating water from reaching waste can slow down the rate of methane production. Ex situ methods involve recovering the vapour or ground gas followed by capture or destruction. Technologies include: • capture via an activated carbon filter, • thermal desorption from excavated soil, • destruction by an incinerator. Page 93
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8 REMEDIATION OPTIONS - Castings Technology International

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