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

4.5.1 Approach• Acid tars are chemically extremely complex with many thousands of individualchemicals, most of which (the asphaltenes) have been characterised to a very limitedextent. When deciding what to analyse for, it is important to have regard to theobjectives of the analysis that is to be undertaken. For example, if the immediatehazard posed to human health is the only hazard that needs to be assessed, thencharacterisation in terms of pH, volatile organic compounds and gas evolution(sulphur dioxide, hydrogen sulphide, methane) may be all that is required;• even very simple analysis can indicate the likely source of the acid tars e.g. BTX atrelatively high concentrations (% levels) will indicate that the acid tars originate frombenzole refining and that risks to groundwater may be higher than for other types ofacid tars due to the mobility and toxicity of BTX compounds;• very simple analysis can also reveal variability between different lagoons e.g. acidcontent can vary between 10 and 90 per cent, water content between 5 and 40 per centand organics content from 15 to 70 per cent;• a more sophisticated analytical approach may be needed in some cases. If anassessment is being made of risks to groundwater or surface water, greater emphasiswill need to be placed on characterising the organic component. In particular,characterising liquid tars and free oils present is likely to be important. This is likelyto include both analysis of samples of free phase hydrocarbons from within the lagoonbut also free phase and dissolved components in groundwater or surface water outsidethe lagoon. The heavy end asphaltenes (high molecular weight viscous tars) may be ofless interest in this context although this is subject to confirmation of thehydrogeological regime and the absence of preferential migration routes off-site suchas fissures, mine-workings etc;• if the purpose of the assessment is to evaluate potential remedial technologies, thencharacterising various layers within the lagoon will be important in assessing thepracticality of handling and achieving intimate mixing in any neutralisation or“dispersing by chemical reaction” (DCR) process. Chemical analysis will also beuseful in this context in assessing the degree of heterogeneity which any treatmentprocess will need to be able to address;• if the tars are to be characterised for waste disposal purposes, then the acceptancecriteria at landfill must be taken into account when developing the analytical schedule.4.5.2 Analytical techniquesAcid tars do pose specific analytical problems, as the highly sulphonated polar residues makechromatographic analysis difficult. Nesbit et al (1995) detail non-conventional analysis usedto characterise the nature of the organic material, including:• class separation by thin layer chromatography/flame ionisation detection to separatearomatic hydrocarbons, saturated hydrocarbons and tarry residues;R&D <strong>Technical</strong> Report P5-042/TR/04 26