Miljøprojekt, 958 – Udpegning af områder med indtrængning af perchlorethylen til indeluften: "Sniffermetoden"

Identification of Intrusion of Perchloroethylene into Indoor Air: The Sniffing Method

Summary and conclusions

This report describes a new method for finding locations with a significant intrusion of perchloroethylene (PCE) from soil pollution into indoor air in buildings. The method has been developed and evaluated in this project, which was supported by the Danish Environmental Protection Agency.

The method is called the “sniffing method”, and its objective is to provide a rapid and cheap tool enabling identification of hot spots with high intrusion of VOCs such as PCE from e.g. concrete floors, or from leaks in building constructions situated at contaminated sites. At the identified locations, and from the survey performed in a grid of measuring points, a quantitative determination of the intrusion can be performed e.g. by means of the “film enclosure method” described in /2/ and /3/.

Furthermore, the sniffing method was tested for use in apartments situated above existing chemical laundries from where a high intrusion of PCE may occur, e.g. due to lack of impermeability of the storey partition between the laundry premises and the apartment.

The sniffing method is based on a device consisting of a flexible enclosure for coverage of the area of the floor, from which the intrusion is to be assessed. The flexible enclosure is placed over the area in question in such a way that minimum contact is possible between the air under the enclosure and the indoor air. After a few minutes, a gas detector can be used for rapid control of PCE present under the enclosure. The air under the enclosure is sucked to the detector via the enclosure's sample point.

The sniffing method was tested in the laboratory. The flexible enclosure was optimised in terms of shape, filling material and type of film used. The photoionisation detector (PI-detector), which was chosen as a suitable gas detector, was tested with respect to response time and measurement range. It was found that a laminated aluminium/Mylar film could be used without any significant risk of adsorption of PCE to the film. Furthermore, the test of the gas detector showed that the PI-detector is suitable for measurement of PCE in a concentration range of 0.5 mg/m³ - 10 mg/m³, and that the response time is less than 60 seconds. It was concluded that the PI-detector was suitable as a gas detector for measurement of the PCE in connection with the sniffing method.

The developed flexible enclosure - called “VaporCover” - was tested at three different locations, where intrusion to indoor air from PCE contaminated soil is known to be present. The locations were a former chemical laundry in a 5-storey building, an existing chemical laundry where PCE has been substituted with hydrocarbons as cleaning agent, and a private villa, situated at a site contaminated with PCE.

In case A, where measurements were performed in the basement under a former chemical laundry in a 5-storey building, the intrusion was measured by means of the sniffing method at a number of points across the basement floor. Measurement points were placed in a grid of about 1m x 1m. A strong intrusion was found from the floor around the penetration of a sewage pipe, where cracks were found in the concrete floor. This confirms earlier findings from emission flux measurements at the same site /2/. No other areas of the floor were found to have any significant intrusion of PCE in case A.

The sniffing method was used as a rapid survey in order to identify “hot spots” with high intrusion in case B and C, and at the identified hot spots, the intrusion was quantified by means of emission flux measurements as described in /5/. In case B, emission flux measurements were performed at the areas with a high and a low intrusion as found in the survey with the sniffing method. From the results from these two measurement points, a correlation between the sniffing method results and the emission flux results was made. From the measurement results found across the floor by the sniffing method, this correlation made it possible to estimate the total intrusion from the floor. In case B, the total contribution to the indoor air from the soil contamination was found to be 0.9 µg/m³. This is significantly below the maximum acceptable contribution of 6 µg/m³ as specified by the Danish EPA. In case C, where measurements were performed in a basement crawlspace, the total contribution was found to be 40 µg/m³, and the maximum acceptable contribution was thus exceeded.

In case D, the intrusion of PCE was measured in an apartment situated above an existing chemical laundry. By means of the sniffing method, a strong intrusion was found from an area on the floor around a doorstep. In this way, a significant leak was identified in the horizontal division between the chemical laundry and the apartment. The result has later been used to improve the horizontal division.

It was possible to use the sniffing method as a rapid and efficient tool to identify areas with a strong intrusion of PCE to indoor air. At areas selected from the survey performed with the sniffing method, the intrusion could be quantified by means of actual emission flux measurements.

In conclusion, the sniffing method was found to be very useful as a tool in a field survey, aiming at locating the intrusion of PCE to indoor air from contaminated soil. When used as a rapid method to locate hot spots, areas for quantitative measurement of the intrusion can be selected, and focus can be directed towards abatement measures. Furthermore, it has been shown through field measurements that the sniffing method can be used in apartments situated above chemical laundries, in order to locate areas with high intrusion of PCE. Thus, the method can be used in connection with the establishment and control of abatement measures, e.g. as described in the Danish EPA's regulations for establishment and operation of chemical laundries.

In this project, the test of the sniffing method focused on the intrusion of PCE. The method may be used for many other VOCs or other gaseous compounds. The possibility to measure other compounds depends on the selectivity of the gas detector used, as the developed flexible enclosure “VaporCover” may be used without modification.

The company Instrumatic AS ^[2] now produces VaporCover commercially.

Fodnoter

[2] Instrumatic AS, Ellemosen 9, 8680 Ry. Phone +45 - 8689 0911, www.instrumatic.com.