Authors:
Jeroen Provoost | Independent researcher | Finland
Dr. Jan Bronders | Vito NV | Belgium
Ilse Van Keer | Vito NV | Belgium
1. Background
Many countries have developed contaminated land management policies to reduce risks to humans and ecosystems originating from soil pollution. One of the major pathways of exposure for humans is inhalation of indoor air as a result of sub-surface contamination with volatile chemicals, called vapour intrusion (VI). Predicting the soil air and indoor air concentration as a result of soil pollution, and the related human exposure, is complex and is affected by numerous factors. Most of the present algorithms for VI calculate point estimates based on a set of default parameter values and therefore give no indication of the variation and conservatism of the predicted air concentrations.
2. Aim
A probabilistic assessment with sensitivity analysis is presented for 6 commonly used VI algorithms. In addition the deterministic default parameter set of each of the algorithms is evaluated against observed air concentrations (benzene, ethylbenzene, trichloroethylene) for accuracy, and against the probabilistic predicted range for the level of conservatism. The screening-level algorithms are ranked according to accuracy and conservatism in predicting observed soil air and indoor air concentrations to determine their suitability for regulatory purposes. To determine the periodization for further actions such as additional measurements or remediation, dominant parameters that drive the predictions, are grouped by physic-chemical, soil or building parameters, and by parameters that are either uncertain or variable.
3. Conclusion
According to this study, the screening-level algorithms that have a higher degree of conservatism for their default parameter set are the Johnson and Ettinger model (JEM), Dilution Factor algorithm from Sweden (DF SE), Vlier-Humaan and VolaSoil. From these 4 algorithms the JEM and VolaSoil have a relative high accuracy (discriminative power). For the latter two algorithms different parameters, that are variable and uncertain, contribute to the variation in indoor air concentration. Differences between parameters that drive the variation were observed between the aromatic and chlorinated hydrocarbons. For trichloroethylene, the default parameter set of Vlier-Humaan, CSoil and DF SE should be adapted to arrive at a higher deterministically predicted indoor air concentration when a more conservative approach is required. The deterministically predicted air concentrations for benzene and ethylbenzene seem to be sufficiently conservative. It is shown that the probabilistic approach allows for an improved insight into the relative importance of parameters in the risk estimates.
4. Reference
Provoost J, Reijnders L, Bronders J, Van Keer I, Govaerts S (2014). Probabilistic Risk Assessment for Six Vapour Intrusion Algorithms, Journal of Environment and Pollution, vol. 3, No. 2, 2014, ISSN 1927-0909 (print), ISSN 1927-0917 (online), Canadian Center of Science and Education, Toronto, Canada, http://dx.doi.org/10.5539/ep.v3n2p1