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Guidelines on remediation of contaminated sites

Appendix 4.2
Soil sampling in connection with borings

For geological determination, soil samples are typically taken at 50 cm intervals; however, at least one sample must be taken for each soil stratum. When investigating the top layers of soil (0-0.5 m) it will be necessary to take samples near ground level.

It will normally be sufficient to take soil samples at 50 cm intervals as regards geological characterisation and PID measurement. Samples are often selected for chemical analysis based on this characterisation and PID measurement. Descriptions of geological characterisation is found in Appendix 4.9.

However, there are cases where it is appropriate to take samples at smaller intervals. In connection with contaminants that are strongly embedded in the soil – such as heavy metals – samples should be taken at smaller intervals around the level that is expected to be contaminated. In connection with oil contamination it may be relevant to increase sampling around groundwater level.

Soil samples are taken as normal stirred samples from a bucket auger or a solid-stem auger. To prevent cross contamination, the outer couple of centimetres must be removed using a clean trowel/scraper, whereupon the soil sample is taken using a trowel/scraper/hollow sampler and put directly into the sample container. Intact soil samples can be extracted using a hollow sampler in cases where optimum sample material is wanted under almost physically intact conditions, or where evaporation of any volatile contamination is not wanted. After purging, the sample is taken from the bottom of the soil boring using a hollow sampler as known from soil engineering /2/.

Normally, 50 g of soil is used for chemical analysis, while approximately 200-300 g is used for geological characterisation. The laboratory extracts test portions of the incoming sample in accordance with the amount needed for analysis.

There are no requirements made for packaging for soil samples that have been extracted for the purpose of geological determination. For instance, the use of plastic bags is widespread. Samples taken for chemical analysis must be packaged in a way that ensures minimum change during transport and waiting time. Soil samples for analysis for volatile substances require extraction in tight-shutting packaging. Table 1 states which types of packaging should be used. Packaging should be completely filled to avoid air above the samples. This is done in order to minimise the loss of volatile substances from the soil samples /1/. It is most practical for the laboratory carrying out the analyses to supply test tubes in connection with analyses of volatile substances.

Table 1
Packaging and storage /3/.

Table 1 shows various forms of packaging, storage, and storage life for various substance classes. The samples must be delivered to the laboratory as quickly as possible. Until delivery, the samples must, if possible, be stores in a dark place at a temperature of approximately 4^oC. (The samples should not be frozen, as this may cause the loss of compounds with a lower freezing point than water). The jars must be kept shut.

An extra set of samples is taken in cases where measurement using a photo ionisation detector (PID) is desired. The samples may be packed in rilsan bags, which inhibit diffusion. Guidelines for measurement using a PID detector are found in Appendix 4.7. As regards disposal of the soil samples, the same conditions apply here as for any other extracted material.

References

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