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

vegetation, black or dark brown staining and, of course, any sign of oozing tars. A rangingrod or similar implement may allow the ground to be probed for evidence of soft ground andtars. As this is withdrawn, any free liquids/tarry deposits remaining on the end may be testedfor pH using appropriate pH papers or detectors.4.3.2 Site investigationApproach to Site InvestigationsIn relation to acid tar lagoons, the following issues are of particular relevance when planning aninvestigation strategy:• likelihood of contaminant migration away from the lagoons (e.g. into groundwater andsurrounding soil);• many sites will have few records of the composition or extent of lagoons, due to theirage, which can be in excess of 100 years. In such cases, aerial photographs can be ofparticular benefit in determining their extent and location, as can local residents andformer employees of the producing works. In some cases, satellite images may beavailable that reveal impacts on vegetation (usually requiring specialist interpretation);• geophysical techniques may be useful in delineating both the extent of lagoons andalso the nature and thickness of the capping layer;• an investigation will need to take into account the presence of features that couldallow migration of tars away from the lagoon e.g. old mine workings, conduits,drainage channels, solution features etc; and• key pieces of information relevant to planning the study include the type of refiningoperation likely to have given rise to the waste, the period of filling, the origin andidentity of fill materials (including any wastes) and any treatment that has been carriedout.A phased approach to site investigation in which exploratory sampling is followed by a moredetailed study is appropriate for acid tar lagoons. However, exploratory sampling may not beneeded in all cases (e.g. where the existence of a lagoon is obvious). In designing thesampling density and locations, it may be possible to restrict the number of samples on thegrounds that it is known that the material is homogenous.Some acid tar lagoons are quite heterogeneous. For example, investigation of an acid tar pitin Derbyshire found that “fill products ranged from materials involved in the process ofreprocessing used oils (tar product, fullers earth and free flowing lubricating oils) to foundrysand, mining spoil and household refuse.”, (Nesbit et al 1995). In this case, during remedialstages, it may be practical to segregate and deal with the different wastes separately and thusgreater quantification via a more intensive sampling regime may be warranted. Where thereare only discrete pockets of non-acid tar wastes all of the wastes are likely, in practice, to betreated as special waste and the variability within the lagoon need not be quantified to thesame degree.R&D <strong>Technical</strong> Report P5-042/TR/04 22