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Kortlægning af diffus jordforurening i byområder. Delrapport 3 Summary and conclusionsThis review report concerning strategies for investigation of the diffuse soil pollution is part 3 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 3 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 of the pollutants 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 less heavy than soil pollution at point sources such as industrial sites or waste disposal suites. The basis for an investigation strategy is that the diffuse soil pollution via the historical description of activities for the area can be related to one or more events that caused the overall diffuse pollution of the area, and therefore can be described by statistical tools. Many individual soil analyses will seldom be sufficient to document that a larger area is polluted since the individual analyses can only demonstrate that the points from which the analysed soil samples are taken are contaminated. More evidence must be provided if the area between the sampling points is also to be documented as contaminated. This evidence can be provided by proposing a conceptual pollution model, which accounts for the origin of the contamination according to the historical description of activities in the area, and by showing that there is a reciprocal and statistically well founded relationship between point measurements within the area of interest, which is in accordance with the proposed model. The planning of an investigation strategy for mapping of diffuse contaminated areas comprises the following systematic steps:
The historical description The historical description including the identification of potential contaminants, spreading to the environment and the possible presence of point sources is prepared. Conceptual Pollution Model One or more conceptual pollution models are proposed to describe the diffuse polluted area taking account of the way (mechanism) in which diffuse soil pollution can have occurred. The nature of the source, the emission, the spreading and expected loading of the soil environmental are important parameters. In the part 1 report summarising the present knowledge concerning sources of pollution and experiences acquired by investigation of diffuse soil pollution, five pollution models have been defined, which are used to define five overall types of strategy. The five models are the deposition model, the line source model, the surface addition model, the contribution model and the soil fill model. Hypotheses The hypotheses, which are to be elucidated during the course of the investigation, are defined. For example that the content of lead in the specified area exceeds the soil quality limit and that the contaminant level is uniform throughout the area and can be represented by an average and a confidence interval. Statistical data needs The data required to calculate both the descriptive statistics; analytical uncertainty and accuracy, log normal plot, cumulative frequency plot, geographical variation across the area and correlation between parameters (e.g. lead and PAH); as well as the geostatistical treatment (spatial statistics), which estimates the geographical correlation and uses this for interpolation of the concentration levels and uncertainty in these across the area of interest. The statistical treatments are used to confirm or reject the hypotheses. In the part 1 report, statistical methods for investigation of diffuse soil pollution are described. Analytical parameters and measurement techniques Based on the historical description of the area and the conceptual pollution model, suitable analytical parameters and measurement techniques are chosen. Previous investigations of diffuse soil pollution have mainly focussed on heavy metals especially lead, oil and PAH, and these are the most critical parameters for most investigations. However, other pollutants such as cyanides, sulphur, sulphate, PCB, phthalates, plasticizers and dioxins may be present and the range of relevant parameters is dependent on the historical description of the area. Since it is expensive to analyse soil samples for all potential pollutants, an advantageous alternative is to initially analyse indicator parameters and if possible to use field-screening techniques to assess the pollution levels and the pattern of distribution across the whole area. After the pattern of distribution is established, a number of representative samples can be sent to accredited laboratory analysis to confirm the content of a wide range of contaminants, which then constitutes the Environmental Authorities decision-making legal basis. In the part 1 report, analytical parameters and results from former investigations of diffuse soil pollution are assessed and reported. Sampling and analytical programme On the basis of the aforementioned systematic steps, a sampling and analytical programme is drawn up. The necessary number of samples and distance between the sampling points is partly determined by the ambition level for the investigation and partly by the natural variation in the soil and distribution pattern. Whether the number of samples is adequate to describe the pollution distribution pattern can be estimated statistically. Most of the pollution models for diffuse soil pollution (deposition model, line source model, surface addition model) give rise to pollution of the topsoil surface and the pollution is not mixed to more than plough depth. This is however not true for areas built on fill (soil fill model) and in the older areas in towns (contribution model). Initiation and execution of the investigation After completion of the systematic steps in the planning phase, the investigation can be initiated. Assessment of the collected information and data with a view to adjusting the hypotheses or strategy must be undertaken continuously. The investigation is reported in a data report and the results are described statistically. During the data treatment, the hypotheses concerning the pollution model and distribution can be confirmed. Conclusions can be drawn as whether the area can be documented as polluted at the legislative knowledge level 2, and if an reciprocal and well founded relationship between point measurements in the area under consideration is established giving veracity to the original hypotheses. It is assessed whether further investigations in supplementary investigation phases are needed. Suggestions for investigation strategies for the five conceptual pollution models including all the systematic steps are given in the report.
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