Opsamling af data for diffus forurening

Summary and conclusions

Current data from examinations of diffuse airborne soil contamination in Denmark has been collected and entered into a database. The extent of the collection is presented in the data report. Data from 3,316 soil samples were collected and analysed for one or more heavy metals or PAH compounds.

Background and objective

For several years it has been accepted that a wide range of activities have led to the environment being contaminated through airborne spreading. It is also known that excess soil from construction works in central urban and industrial areas is often contaminated. Today excess soil is checked and deposited in areas that are suitable for the degree of contamination of the soil. For many decades excess soil was used for filling old gravel pits, low-lying areas and as backfill under new urban developments.

This contamination is generally termed diffuse soil contamination as there is no sharp delimitation against clean areas, and very often no unambiguous relation to the source of contamination can be pointed out.

Diffuse soil contamination is typically encountered in old city areas, areas that are built on backfill derived from urban centres, along major roads and in the vicinity of metalworking companies.

The objective of this project has been to increase general awareness and knowledge about diffuse soil contamination. The objective has been pursued by collecting and systematising existing data from examinations of diffuse contamination in urban areas, along roads and in areas with backfill originating from city centres.

The survey

Samples were collected from Denmark’s 14 counties and the municipalities of Copenhagen and Frederiksberg. A few other major municipalities have also been contacted with a view to collecting supplementary data material.

3,316 soil samples were taken close to the surface of the ground. The sample data was entered in the DifJord database, developed in Microsoft Access 97, operating system Windows 95. The material in the database gives a greater understanding of the extent, nature and coherence of the diffuse soil contamination.

Analyses from the DifJord database indicate a total of 15,776 results for heavy metals contamination and 19,782 results indicating contamination by PAH compounds. In addition, the database contains 609 instances of hydrocarbons in the analysed soil samples.

A great deal of information is linked to the individual analysis results in terms of sampling, soil description, pre-treatment of test material, sample digestion, methods of analysis. In addition, source type, possible distance and direction have been recorded for examinations providing information about possible sources of contamination.

Main conclusions

An overview of the sampling has been made, and the systematising of the data has given others the opportunity to process existing data with a view to determining relationships between cause and effect, establishment of "normal levels", coherence between soil types and contamination, depths and distances and similar correlation.

Project results

Samples were collected from a number of counties and municipalities across the country. The collected data does not reflect an average of diffuse soil contamination in Denmark. This is due, among other things, to the disproportionate geographical distribution of the number of soil samples taken.

We have chosen to abstain from calculating mean concentrations of the various parameters processed in the database. Calculations of mean values of the individual substance parameters may be deceptive as a consequence of the data material which, as mentioned, represents a disproportionate geographical distribution of the country and in a number of cases represents local conditions in connection with a contamination source.

Subsequent processing of the samples indicated that data from different parts of the country will of course vary as a consequence of the overall natural variation in the "true" background level of the areas.

The collected data shows that at present the diffuse contamination is a condition that has typically been examined in major urban districts - i.e. the Copenhagen area, the county and municipality of Århus and, partly, the municipality of Odense.