How to model...

How to interpret the results of the risk table of application II (RI, ExCR, pRI and CI values)?


Application II reports the results of the risk assessment under the form of a table, giving risk values for – potentially – three major groups of effects (threshold, non-threshold and pseudo-threshold). A further distinction is made between systemic and local effects.

Why are indoor air concentrations/risks for the 'intact' floor type sometimes higher than for the 'gaps and holes' floor type?

Following the Volasoil guidance, the floor type 'gaps and holes' (which is the default setting in S-Risk) is considered the worst-case approach resulting in the highest predicted indoor air concentrations.

How to model the situation of a basement in contact with groundwater?



In case you need to assess risks due to vapour intrusion in a building with a basement in contact with groundwater, careful evaluation of local site conditions is required:

Why does S-Risk give a warning message for a calculated critical concentration in application I or III?


In applications I and III, S-Risk tries to find critical concentrations corresponding to certain threshold risk levels ((pseudo)risk index or concentration index is 1 or excess cancer risk is 1/105). In mathematical terms, S-Risk executes an optimization algorithm that searches the lowest soil/groundwater concentration at which, for instance, the risk index becomes more than 1.

S-Risk has some known inconsistencies in the soil-to-outdoor-air emission model. What is their impact?


The soil-to-outdoor-air emission model in S-Risk has some known inconsistencies. Under certain circumstances, it is possible that air concentrations predicted from topsoil contaminated layers are lower than air concentrations predicted from similarly contaminated, “buried” layers. This is counterintuitive and not realistic.

How to deal with combined soil layer & groundwater contaminations?


When a contamination is present in both soil and groundwater, both concentrations can be entered simultaneously in S-Risk. S-Risk will first calculate the outdoor and indoor air concentrations separately for each soil layer and for the groundwater layer. Afterwards, the maximum of these calculated outdoor air concentrations and of each indoor air concentration (if the scenario requires such) is taken forward to the exposure assessment and risk characterization step.

What is the best way to model a contamination below groundwater level?


S-Risk allows to define soil layers down to the groundwater table, but not lower. For situations with a contamination beneath groundwater level, S-Risk calculates transfer based on the groundwater concentration (affecting volatilization, permeation and exposure pathways with direct use of groundwater).

At this stage, it is uncertain wether we will implement the models needed for such "submerged" soil layers in S-Risk.

However, there is a workaround for situations like these:

How to deal with basement air measurements?


The modelling concept for vapour intrusion to indoor air considers the basement and the indoor of the building to be one volume. Therefore, it is not possible to enter measured concentrations for basement air in the model in the Concentrations tab.
Several approaches could be used to assess this situation as correctly as possible:

How do we cope with a crawlspace with a concrete floor?


The modelling concept for vapour intrusion to indoor air assumes that the crawl space has no floor, i.e., the crawl space is in direct contact with the soil. If you have a crawl space with a concrete floor, then the model concept will overestimate concentrations and be too conservative.

For simulating a crawl space with a concrete floor, you can take a stepwise approach.


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