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

• to ensure the safe disposal of acid tars, treatment or at least partial treatment will berequired involving some form of neutralisation (discussed in Section 6.2.5).6.2.2 Biological based technologies• Biological based techniques involve various forms of ex situ bioremediation, such asbiopiles, landfarming, slurry phase biotreatment, windrow turning and in situprocesses, such as bioventing. These techniques do pose difficulties for acid tars, dueto their acidity, high concentrations of organic compounds and problems with bioavailability;• the use of bioremediation requires neutralisation (or at least raising the pH to 5) via anintimate mixing of the tar and a neutralisation agent such as calcium oxide or calciumcarbonate. The mixing process can be prohibitively difficult to achieve (see 6.2.5,below);• even where neutralisation is achieved, the issue of bio-availability remains. Thecontamination as a solid mass is difficult to degrade due to its very low surface area :volume ratio. In order for significant degradation to take place, it needs to be fullydispersed as a suspension of fine particulates within a medium supplied with sufficientoxygen and nutrients. Given the solid nature of the tar this is difficult to achieve, evenusing specialist plant and equipment. Nevertheless, where these constraints can beovercome, it is of interest as a sustainable technique.6.2.3 Chemical based technologies• The only potentially applicable chemical based technology is that involving surfaceamendments (e.g. organic matter or an alkali such as lime), and only for surface orshallow depth contamination (see Remedial Treatment Action Data Sheets,Environment Agency 2001);• the key problem is ensuring a suitably intimate mixture of lime and tar, since evenwith specialist plant this is likely to be difficult to achieve in situ especially with alagoon of acid tar present. In any case, very large quantities of calcium oxide(quicklime) or other alkali may be required. A more advanced method may beappropriate, however, such as ex situ treatment or the use of a proprietary approachsuch as “Dispersing by Chemical Reaction” (DCR). DCR and lime-based systems arediscussed further in Section 6.2.5.6.2.4 Physical based technologies• Air sparging and soil vapour extraction are not applicable to acid tar lagoons due tothe fact that most of the contamination will be of low volatility;• various washing systems may be applicable to associated contaminated soil but willnot address the explicit tar deposits.R&D <strong>Technical</strong> Report P5-042/TR/04 34