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

2.1.2 Overview of acid tar lagoon sitesGeneral points regarding acid tar lagoon sites include the following:• acid tars have historically been generated as by-products of benzole refining, refiningpetroleum fractions (particularly white oil) and oil re-refining;• the nature of the acid tars will depend to a degree on their origin. For example, acidtar arising from a specialist refinery processes involving the treatment of petroleumfractions with sulphuric acid may comprise black, tarry deposits. However, that fromwashing of benzole (BTX fractions) with sulphuric acid may be an odorous darkcoloured liquid;• acid tars have a very variable composition between sites and even within one lagoon,but are usually characterised by a weathered, crusty and relatively solid surface, withmore fluid tars below;• in situ, acid tar comprises a mass of hydrocarbons that is generally viscous and tarrywith low pH. Layers of acid tar may be separated with intermittent soil layers or otherdeposited wastes;• surrounding soils are likely to be contaminated to varying degrees with tars andhydrocarbons;• some lagoons, in particular the older ones, are likely to have been filled with untreatedtars. This was done either as a temporary measure to allow weathering to reduce theacidity, prior to disposal or incineration, or as the permanent disposal method. Themore recently deposited lagoons may contain partially treated tars. Treatment mayhave been by the use of lime, in an attempt at neutralisation, or by igniting the tars insitu;• attempts will usually have been made at covering or capping the tars, often with soil,sand, ash or domestic refuse. However, fluid tars can ‘bleed’ to the surface and solidcapping material may sink into them. The tars that rise to the surface can expand andsoften further in the sun and, potentially, may overflow resulting in movement off-site;• some acid tar lagoons have also been used as disposal sites for other materials and it isnot uncommon to find other wastes such as demolition materials and chemical drumsin the lagoons.2.1.3 Origins of acid tarsAcid tars have been generated historically in the UK as by-products of three distinct industrialprocesses (consistent with the definition of waste acid tars in the Contaminated <strong>Land</strong>(England) Regulations 2000):R&D <strong>Technical</strong> Report P5-042/TR/04 7