The odour impact in this study was assessed based on the results of olfactometry and the
previous 5-year weather data. It can be indicated that odour concentration at the nearest air sensitive receivers (Office Buildings 1 and 2) of the landfill site is always below 5 ou/m3 with a chance of 99.99% based on the yearly, monthly and daily average weather data, and odour
concentration at the boundary of the landfill site is higher than 5 ou/m3 with a chance of more
than 0.01%, based on the hourly average weather data. However, it may not be a good
approach by simply applying the “pass” and “fail” attitude in the practice of odour impact
assessment. The concentration component of the odour modelling guideline gives the
indicative level of odour nuisance, but that any concentration predicted by the model within a
factor of two of the boardline may not indicate whether adverse effects will occur. For
example, the concentration component of the odour modeling guideline in Hong Kong is
5 ou/m3. If the model results were less than 2.5 ou/m3, then it could be concluded with more
confidence that no significant adverse effects would occur. Similarly, if the model results
were greater than 10 ou/m3, then it could be concluded that significant effects were more
likely to occur (subject to assessment of the sensitivity and conservatism in model results).
However, if the model results fell into the “grey area” range between 2.5 and 10 ou/m3, then
the evaluation process would need to rely more heavily on a subjective assessment of the
model results, and other methods in the evaluation “toolbox” to assess the potential for
adverse effects.