Page History

...

Question:
I would like to know, if the assessment would be satisfactory, if I use an average value and thus use an exponential distribution or should I use the average + SD and use lognormal? An average value is an average of 12 samples taken each month through year from one monitoring place. So SD are calculated from 12 samples from one monitoring place and are not related to different places in specific
river. The assessment with average value without SD should represent satisfactory results compared to average + SD in my case? Dose rates should be in the same range when using exponential or lognormal?

Answer:
Easy art of your question first - your mean estimate when using a mean and pdf in Tier 3 of the ERICA Tool will be similar to estimate using Tier 2 and inputting a mean value only; it will not be exactly the same as Tier 3 is probabilistic. The mean estimates using either a lognormal or an exponential distribution in Tier 3 will be similar. The percentiles, minimum and maximum values will be different and dependent on the SD used for the lognormal distribution_.

Which should you use? As is often the case there is no definitive answer to this. It depends what your criteria are - do you want to ensure your assessment is conservative? If yes then try both distributions in the Tool and compare your answers - it is relatively straightforward to do.

You appear to be questioning how representative your input data are? I'm afraid that you are best laced placed to answer this yourself. However, if your data are from close to your the release source then you can have some confidence that they will give a conservative assessment downstream. If your data are distant from your the source and you want to ensure populations upstream from your sampling site are protected then you need to obtain more samples form from approriate locations or make predictions using a dispersion model.

...