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

5.2.3 Ecological systemsThe risks to flora and fauna from the contaminants in acid tar lagoons together with vapours andgases produced, are similar to many other contaminated land/landfill sites. The clear exceptionto this is the severely acidic conditions that exist, particularly where acid tars have “bled” to thesurface and the effects on flora and fauna that come into contact. The actual ecological issuesneed to be assessed on a site specific basis.5.2.4 BuildingsAcid tar lagoons are ordinarily not built upon due to inherent stability problems and it is mostunlikely that an acid tar lagoon would be developed without addressing risks to buildingsassociated with the tars.There may occasionally be a risk to buildings or infrastructure such as roads associated with asudden release of acid tars down a slope where these are held back by fragile supportingbanks, especially where these are made unstable by engineering works nearby.As indicated previously, acid tar lagoons may emit methane, hydrogen sulphide and othergases as a result of naturally occurring degradation processes. However, explosive orflammable levels of the former are unlikely, due to the relatively small quantities involved,and, in any case, buildings are very unlikely to have been placed directly on top of a lagoon.The possibility of lateral migration of gases off-site should be considered especially whereareas of hardstanding are present and there are nearby buildings.5.2.5 Generic pollutant linkage matrices for acid tar lagoon sitesA variety of pollutant linkages may be identified on acid tar lagoons and examples are givenbelow. These are meant only as an initial guide to the types of issues and are not intended tobe a substitute for the site-specific assessment which will be required in practice. Howeverthey should provide an initial indication of the pollutant linkages which should be consideredin the site-specific assessment.Table 5.1 - Examples of Pollutant LinkagesSource/HazardAcid tars exposed/near surfacePathways/ReceptorsTrespassers/visitors to the site and fauna– skin contact,vapour inhalation, fire risk, risk of sinking into tars.Neighbours – odour and hazardous vapours/gases.Flora – unsuitable physical and chemical conditions,poisonous soil gases.Acid tars at depth (e.g.>1 m Groundwater/surface water depending on thebelow surface)hydrogeological and hydrological regimes.Instability Buildings/infrastructure/personnel downslope –migrating tars and liquids.R&D <strong>Technical</strong> Report P5-042/TR/04 30