Land Contamination: Technical Guidance on Special Sites: Acid Tar ...

Investigation locations will need to be re-instated and clean cover material used to coverexposed wastes. On some sites, the surface topography might suggest that local superficialsoils may be “borrowed” for this purpose. However, great care should be taken in this toavoid inadvertently digging through into underlying wastes and exacerbating problems. It isusually necessary to make sure that there is a supply of clean imported cover material fromthe very start of an investigation. Each location should be re-instated in turn as it is finished,rather than re-instatement carried out as a self-contained exercise after all locations arefinished. This is particularly important where the site is not entirely secure from publicaccess.Sampling TechniquesConventional sample collection procedures during intrusive works are relevant to samplingfrom acid tar lagoons, provided consideration is given to the potential for highly acidicconditions and the presence of free hydrocarbons and volatile organic compounds. Thus:• sampling containers should comprise amber glass jars with PTFE seals as a minimum(plastic sampling pots are unsuitable); and• once collected, the samples should be stored at a controlled temperature of between2°C and 4°C and be delivered to the laboratory within 24 hours of collection.The sampling of surrounding media, if performed, should also be conducted in the light of thelikely contaminants (e.g.. low molecular weight hydrocarbons in air/groundwater and acids ingroundwater).Gases should be measured in boreholes using appropriate instruments. In some cases, it maybe useful to collect Gresham samples for laboratory analysis. Note that aluminium Greshamtubes can absorb hydrogen sulphide and so should not be used where analysis for this gas isrequired.Early consideration should be given to the methods of, and equipment needed for, thecontainment and disposal of contaminated purge-water.4.4 Common MistakesToo much attention may be paid to the sampling of the solid tars themselves whereas it islikely to be the liquid tars, free oils and aqueous phase that are more environmentallysignificant.4.5 Chemical AnalysisNote - this section should be read in conjunction with Section 3.3, which provides analyticalinformation on acid tars.R&D <strong>Technical</strong> Report P5-042/TR/04 25