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Kortlægning af diffus jordforurening i byområder. Delrapport 1 Summary and conclusionsThis review report concerning sources of diffuse soil pollution is part 1 of a three part report prepared under Phase I of a project on mapping of diffuse soil pollution in urban areas. The project is instigated and supervised by the Agency of Environmental Protection in Copenhagen under the Danish Environmental Protection Agency's technology development program. The overall objective is to prepare methods to optimise and simplify technical investigations by the environment authorities in connection with mapping of diffuse soil pollution at the legislative knowledge level 2. Phase I has included a review of information concerning the sources of pollution, measurements from actual investigations, analytical and sampling techniques and investigation strategies. The objectives for the part 1 report are;
Diffuse soil contamination is originally caused by events that are related to one or more point sources, but where emission, transformation and dilution in other media has occurred, so that the relationship between the pollution source and the soil contamination is indistinct. Diffuse soil pollution is not restricted to areas close to a point source and will typically comprise contributions from many sources. Sources of diffuse soil pollution are therefore difficult to identify and the diffuse soil pollution is typically less heavy than soil pollution at point sources such as industrial sites or waste disposal suites. Areas that have been contaminated by a range of different activities over a longer period of time e.g. culture layer in old city sites or due to larger earthworks with contaminated fill during construction projects, site preparation, land reclamation etc. can all be defined as diffuse soil contamination. In this part 1 report, five conceptual pollution models have been defined which describe the way in which diffuse soil pollution can occur. For all five models, the chronological time-frame for the emission to the environment is of importance and a detailed historic description is a prerequisite for the mapping and documentation of diffuse soil pollution at knowledge level 2. These aspects are especially pertinent with respect to clarification of the potential types of pollutant present and the conceptual model for the soil contamination, but also with respect to identification of point sources in the area under consideration. The categorisation of diffuse soil pollution is this report is based on the five different approaches:
Town development Towns have always been centres for housing and many small industries. It can be expected that in former times, both waste from trades and industries as well as waste from domestic housing has found its way to the nearby soil environment. Demolition of derelict buildings or town fires will often have resulted in the addition of various construction materials and fire residues to the topsoil. Smoke, soot and waste from domestic heating can also have been a source of pollution to the local soil environment. Typical pollution parameters are PAH, oil, heavy metals; Pb, Cu, Zn, Ni, Cr, Hg and Cd. The local infrastructure, line sources such as roads and railways, can also have contributed to the diffuse soil pollution and the degree of soil pollution will often be dependent on historical details such as the time period for construction works, traffic density as well as speed regulating structures (speed restriction zones, traffic lights, crossroads). Typical pollution parameters are PAH, oil and heavy metals; Pb, Cu, Zn. Industrial Sources Local point sources (industry) will often have produced an important contribution to the diffuse soil pollution by wet and dry deposition from smoke and other emissions, by establishment of local industrial waste dumps or by construction of earthworks with contaminated soil. Typical pollution parameters are in part dependent on the type of industry, but generally include PAH, PCB, phthalates, oil, heavy metals; Pb, Cu, Zn, Ni, Cr, Mo and Cd. Furthermore, atmospheric deposition of PAH and heavy metals from distant sources can contribute to soil loads. Distant sources only cause an even loading over large areas of topsoil and the contribution to the diffuse soil pollution across a given area is expected to be very small in comparison to contributions from other local sources. The cumulative effect is most evident in undisturbed soil, where the atmospheric contribution accumulates in the upper few soil cm. Ploughing and cultivation of the soil cause dilution in the soil layers of the pollution constituents accumulated by way of atmospheric deposition Investigations of emission Investigations in both Denmark and in other lands have comprised measurements in the atmosphere, and deposition rates for constituents such as heavy metals, soot, airborne dust, PAH, PCB, dioxins, phthalates and DDT. The highest values are seen in towns especially close to industrial sources of pollution, but also in rural areas, a pollution effect can be detected in the atmospheric air and in deposition. Investigations of soil pollution Danish soil investigations of diffuse contaminated soil have shown that a diffuse soil pollution has a very close relationship to traffic, or to older areas of towns or to large point sources of pollution. Point sources like metalworking industries can, for example, contribute to increased concentrations of the topsoil in a radius of 100 m to 6 km from the sources. The Danish investigations have mainly been carried out to assess possible conflict in land usage due to non-compliance with the Danish soil quality criteria. For these reason the most common parameters in these types of investigation are for contaminants with designated soil quality criteria, i.e. heavy metals, oil and PAH. Investigations of diffuse soil contamination in towns in other countries have shown similar levels to those seen in the Danish investigations. Statistical data treatments In many of the investigations from other countries, statistical data treatments such as frequency analysis, normal distribution, etc., have been applied to evaluate the pollution data. Furthermore, geostatistical methods to separate comparable data (same population, e.g. diffuse soil contamination) from non-comparable data (e.g. point sources). Geostatistical methods are used to evaluate the spatial distribution of the geochemical data. These techniques an be used to:
Geostatistical methods calculate variance, i.e. the statistical difference between data values localised in different distances from each other and where all data within a defined distance is compared in pairs. Conclusions It is concluded that diffuse contaminated soils in towns usually demonstrate non-compliance with Danish soil quality criteria for PAH and lead by a factor of about 2-3. Higher soil concentrations are seen close to point sources or line sources (roads). Furthermore, raised content of many heavy metals such as copper, chromium, nickel and especially zinc is seen, although the Danish soil quality criteria are seldom exceeded. The most critical sources of diffuse soil pollution are assessed to be deposition from nearby point or line sources or associated with the former history of soil utilisation, e.g. urban activities. The term history of soil utilisation not only refers to previous industrial activities, but also earthworks, type of soil fill, soil cultivation and treatments, terrain levelling, urban age and activities and to building demolition and town fires. Typical pollution parameters in the urban culture layer are PAH, oil, heavy metals; Pb, Cu, Zn, Ni, Cr and Cd. Furthermore PCB and dioxins can be potential contaminants.
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