Case

Optical light discovers contaminated soil

NIRAS has completed a successful inspection of contamination in Kungsbacka in Sweden with a completely new technology that both exposes the contamination in the soil and saves the client for countless expensive soil sample analyses.

In the city Kungsbacka in Sweden, project manager Freja Rebecca Johansen has just ended a contamination screening of an area. A roof and building paper factory were located here and large amounts of tar among others have contaminated the soil. NIRAS is mapping the distribution of contamination.

Since 1998, NIRAS has– as one of the first ones in Europe – used the Geoprobe system, where a drilling rig pushes a probe down through the soil layers. The probe registers contamination levels of each 1,5 cm and is able to detect even minor concentrations of both oil, creosote and tar. The method is thereby able to map the distribution of the contamination and the requirement of soil samples is significantly reduced compared to traditional contamination inspections.

New method makes the contamination luminous

However, the assignment in Kungsbacka is remarkable in a different way, as it combines the Geoprobe with the use of a new probe called OIP (Optical Profiling Tool). A little light source, transmitting a UV-light is placed inside the probe. The light makes the contamination with hydrocarbons fluorescent and thereby the signal can be captured by a camera. Besides UV-light, the light source can transmit a green light – a so-called G-light– in order to capture heavier substances such as tar and creosote.

”With this new method combined with the Geoprobe, you get a very distinct picture of where the contamination is located. We both get the type of soil exposed and an indication if it is either lighter or heavier oil components that are present in the free phase,” says project manager Freja Rebecca Johansen.

Saves the customer expensive soil samples

In the so-called free phase, the concentration of contamination is so high that the contamination is present as completely liquefied small drops in the soil’s so-called pore barrier. When the pores are filled, the contamination is able to flow through soil cracks and in this way moves down through the soil. If the contamination is not removed it may ultimately end in the groundwater.

”The OIP-camera takes regular pictures so it is possible to see that the contamination actually is present. Subsequently, individual soil samples can be conducted at the locations where the Geoprobe with OIP has proved contamination in order to confirm the presence of it. In that way, the customer saves both a lot of unnecessary expensive soil samples and can map the distribution of the contamination faster and then deploy the preventive actions faster,” she continues.

An effective remedy for contamination in Sweden

As the first ones in Europe, NIRAS got the equipment for conducting OIP-inspections in 2016 and is the only consultant company that is using it at the moment. In corporation with Sveriges Geologiska Undersökning (SGU) among others, NIRAS conducted a number of inspections of contaminated soil – among others in Kungsbacka.

”We have very good experiences with NIRAS’ use of the OIP-method, as it has provided us with lot of data in 3D and thereby a possibility to establish a good conceptual model,” says Erik Bergstedt fra SGU.

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Freja Rebecca Johansen
+45 2671 7465

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