Professor, recently I'm wondering whether we can apply the principles described in the ASTM E2600 guildline to forecast the potential health risk based on the structual characteristic of the buildings, combined with the function of them(e.g. as residential building, office building or others), to be built vertically above an area heavily contaminated by BTEX. You see based on the assessment results from the prevailing RBCA_toolkit, the risk is too conservative. So now we resort to the following approaches to emend the results: Firstly, we are planing to measure the flux of the COC and then estimate the exposure concentration under different scenarios through the related models, with the corresponding risk being calculated followed. But given the lack of experience and so much uncertainty, as well as so many variables, in the measurement process, we are not so confident with the final results. So we are considering whether we can use the soil gas, the measurement of which is not so heavily affected by the surrounding  enviromental factors, as the baseline value to predict the exposure concentration by mutiplying it with an attenuation factor. If this approach is defensible, how can we make  reasonable decisions on the following two matters:1) the depth of soil gas sampling point; 2) the value of the attenuation factor;

Thanks in advance and look forward for your opinions