Miljøprojekt, 913 - Teknologiudviklingsprogrammet for jord- og grundvandsforurening – Diffus jordforurening og trafik - Delrapport 3

Summary and conclusions

This data report presents the data collection and results for the investigation of diffuse soil pollution caused by emissions from traffic. The report concerns data collection and results for the investigations of diffuse soil pollution along two different road sections.

The data rapport is one of four reports prepared in connection with a project initiated and supervised by the Agency of Environmental Protection in the City of Copenhagen under the Danish EPA Technology 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.

Test area

The investigation was carried out on two different section of Hareskov road and Frederiks road, both established at least 60 years ago and both have a traffic density of 20,000 - 48,0000 cars a day.

Conceptual model

The diffuse soil pollution alongside the main roads is assumed to be described by

a line model due to emissions from traffic and the road construction

Hypotheses on the line model

It is assumed that the contamination consists of lead and other heavy metals, PAH, oil, pesticides, dioxins and phthalates. It is assumed that the pollution decreases with distance from the road, and that the contaminated area extends to at least 30 m from the road verge. At greater distances, it is assumed that the level of contamination is determined alone by the other diffuse sources of pollution (historic fill – contribution model). It is assumed that the soil pollution decreases with depth.

Experimental plan

in the line model contamination levels in the sampling positions along the two test sections of road are expected to decrease with distance from the road and in depth. To document contamination levels and dependency of distance from the road, samples are taken from sampling areas placed at different distances form the road verge. To determine variation in depth, samples are taken at different depths down to 1 m.

In all samples, indicator parameters are measured, and selected samples are analysed for other additional parameters.

Results

Generally, it is concluded that the contaminant pattern along the test road sections can be described by the line model within 0 – 15 m from the road verge, while areas at greater distance from the verges can be described by the contribution model.

Large variation in concentration levels is observed in samples close to the road, and it is assumed that soil along the verges is arbitrarily removed or planed in connection with road maintenance or renovation.

Generally, the contamination levels are highest in the upper soil layers (contribution form the surface), but can penetrate to a depth of at least 30 cm.

A comparison of PAH composition in soil samples from the test areas in housing areas with historic fill or contamination from industrial stacks and soil samples taken close to the two main roads indicates that three PAH indicators that are expected to indicate emission from traffic, are elevated in soil samples close to the road. While the analysis of additional PAH to assess the PAH composition has indicated some interesting relationships, these are often indistinct, presumably due to the many sources that contribute to the PAH load in soils. Assessment of PAH composition is especially interesting in connection with characterization of pollution sources, but does not aid appreciably in the mapping of diffuse soil pollution.

Heavy metals, oil and PAH

Generally, soil quality criteria (JKK) for lead, BaP and cadmium are exceeded in soil samples close to the road, and a few samples exceed the soil intervention level (ASK) for BaP. Copper and zinc contents are elevated in comparison to urban background levels, and a few samples exceed JKK. The content of lead, copper and zinc in soil samples are correlated to a certain extent.

Soil quality criteria for hydrocarbons (oil) are exceeded in about 50% of soil samples in the upper soil layers (10 cm). Oil contents of up to 700mg /kg dw have been measured.

Measurement of PAH is an important parameter, but BaP is the most critical PAH parameter. Measurements of seven PAH can be used to control if there is agreement between the content of BaP and DiBahA (dibenz(ah)anthracen), in that individual PAHs are directly correlated

PCB

PCB was generally not found in soil samples alongside the two roads (no PCB was detected in 85% of the samples)

Phthalates

Low content of phthalates was detected in all samples, but the JKK is not exceeded. The content of phthalates taken in samples immediately alongside the road is slightly elevated compared to samples at a greater distance from the road

Dioxin

All the analysed soil samples had a low content of dioxins (2 - 8 ng international toxic equivalents (ITE)/kg DW). There is no Danish JKK, and therefore the toxicological aspects cannot be assessed. However in Germany, the background level in rural and urban areas is 1- 5 ng ITE/kg dw and 10 – 30 ng ITE/kg dw respectively.

Pesticides

The pesticide content (only pesticides with slow degradation times) was determined in nine soil samples, but only low levels of DDT were found in three of the nine samples (0,005 - 0,018 mg/kg dw). The JKK for DDT of 0.5 mg/kg dw was not exceeded.

Experiences concerning the strategy

Analytical parameters

The important pollutants in diffuse soil pollution along roads are lead and benzo(a)pyrene (BaP). Supplementary analysis for other heavy metals (cadmium, copper and zinc) and sum of PAH will lead to a better description and documentation that the contaminant levels along the road section lie within the expected range, and to identifying possible contaminant loads from other sources.

Experimental plan

The experimental plan for the investigation of diffuse soil pollution and traffic was based on random sampling in 2 by 2 m (4m²) sampling areas placed at different distances from the road.

It was assumed that the contaminant levels within a distance zone – e.g. Zone A 0-2 m from the road – are comparable. In other words that the content in soil samples from the same depth in each zone should lie within a narrow confidence interval. However, variation in concentration levels within a zone was high, while variation in the individual 4 m² sampling areas was low.

To ensure that the contaminant levels can be evaluated in relation to position along a road, it is recommended that a future strategy should comprise sampling in 0 - 20 m profiles at right angles to the road.