soil vapour testing

Redeveloping sites such as this former powder coating and spray-painting business can become a much more costly activity when a historic Trichloroethylene (TCE) tank turns up during the routine environmental due diligence stage, and TCE contamination is suspected.

But what is TCE? TCE is a cleaner/degreaser that was historically used extensively in industrial processes and can remain in soil, and migrate to groundwater. Over time, TCE can manifest as soil vapour which in turn poses a risk to human health from the potential migration of the vapour to indoor air. Exposure to TCE can then result in a range of acute and chronic health effects and can affect the central nervous system, in addition to causing liver and kidney damage. As TCE degrades, it can form carcinogenic by-products. Therefore, when it comes to the redevelopment of such sites, as was the case with this site near Auckland's CBD, it's crucial to understand whether TCE in the soil (and its subsequent quantities) is also present as soil vapour in the sub-slab at concentrations which may pose a risk.

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For this particular project, in order to investigate the presence of soil vapour beneath the existing building, 4Sight installed 10 Soil Vapour Pins™ across a basement concrete slab down-gradient from the TCE tank. This method, although used globally, is not something many companies in New Zealand are currently offering, and its benefits far outweigh those of other traditional extraction methods. This is because the installation of the pins themselves is fast (in this case 10 sample pins were able to be installed in a single day) and its ability to allow for sampling the following day.

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Sampling results for this project indicated TCE concentrations in soil vapour that were up to six-orders of magnitude above the adopted human health assessment criteria immediately beneath the concrete slab. Concentrations of TCE were so elevated that the analytical laboratory had to dilute the soil vapour samples to prevent damage to their analytical equipment.

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While the presence of soil vapour in the sub-slab environment was not indicative of actual migration to indoor air, the highly elevated concentrations of TCE recorded as soil vapour suggested that there was a high potential for risk to human health. Based on the results of the soil vapour sampling, it was determined that the property was not suitable for the proposed re-development without implementation of appropriate remediation strategies.

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Watch our video on Soil Vapour Pins™ below and check out the image gallery: