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

• there are very few records relating to the locations or the methods of acid tar disposalused. It is believed, however, that even at the larger re-refining sites there was little orno treatment of acid tars prior to disposal (this being usually on-site or close to theplant);• there may therefore be a number of sites as yet undiscovered, which could have acidtar lagoons present.Box 2.4 Scenario: What quantity of acid tars might be found at an oil rerefiningsite?If we assume, based on the above, that a refining plant produced typically 500tonnes of acid tars per year then 40 years operation would correspond to 20,000tonnes.An acid tar disposal area for a re-refinery that was remediated in the 1990s costapproximately £1 million to address*. It involved excavation and re-depositionin a licensed landfill as special waste (presumably after mixing with othermaterials). This cost would be broadly consistent with the quantity of acid tarsindicated above.* further details confidential2.2.3 Uncertainties and unidentified sitesA definitive list of the location of sites where acid tar has been deposited is not available andthere may be unidentified sites. However, from the discussion above, acid tar lagoons arelikely to occur at:• about 140 former benzole refining sites near larger gasworks and at coke-making sites;• about twelve major oil refineries (white oil production); and• about 30-40, mainly small, oil re-refining plants.2.3 Key Site Features• Disposal of acid tars is likely to have occurred in the most convenient location on ornear the site in the easiest manner for the site operators as possible;• topography, proximity and availability often controlled the choice of locations fordisposal sites;• on large sites, such as major refineries, disposal may (particularly more recently) havebeen within an engineered repository but cruder disposal is likely to have beenpractised historically in most situations, especially on smaller sites.R&D <strong>Technical</strong> Report P5-042/TR/04 12