How to deal with a contamination that is only partially situated below a building?

Rule n°1: Always check the rules applicable to your region in order to see for which scenarios you can use this outlined approach, and for which not.

Situations with buildings under which there is only a partial soil contamination with chemical substances, can be simulated by enabling the "separate profile for indoor vapour intrusion" in the "Soil concentrations" section ob the "Concentrations" tab.
 
The soil concentrations in the separate profile need to be calculated taking into account the area of the contamination and the area of the building (or basement) floor. This is done by multiplying the concentration in the contaminated soil under the building with the area of the contamination below the building and dividing it by the full area covered by the building (or basement) floor. For example, if the soil contamination is only present below 30% of the building surface, the calculated concentration equals 30% of the measured soil concentration.
 
This modified concentration needs to be entered in the rightmost field (the "indoor profile") of the Soil concentration panel on the Concentrations tab; the concentration representative for outdoor calculations needs to be entered in the leftmost field (the "default" profile). The soil concentrations entered in the separate indoor profile will only be used for the calculation of evaporation to indoor air. Other parameters, such as surface area of the floor, volume of the indoor space, and so on, should not be modified as they also impact S-Risk calculations other than evaporation to indoor air. By following this method, you will receive a more accurate estimate of the risks given a partial soil contamination below a building.
 
S-Risk does not allow you to use the same approach for groundwater, as this will inadvertently impact other calculations too (e.g., for outdoor air and in some cases, drinking water). Moreover, groundwater contaminations are very mobile in contrast with soil contaminations. Only when you can convincingly demonstrate that the groundwater contamination is only partially present below the building (e.g., groundwater contamination only present below 30% of the building surface), you may perform the following two-step approach.
  1. Perform a simulation in S-Risk in which you enter (at the Groundwater concentration panel on the Concentrations tab) a groundwater concentration that equals, e.g., 30% of the actual measured groundwater concentration. This simulation will provide you with a calculated total indoor air concentration, to be found in the detailed PDF report of your simulation.
  2. Perform a second simulation in S-Risk in which you enter (at the Groundwater concentration panel on the Concentrations tab) the actual measured groundwater concentration. At the "Concentrations in transfer media" panel on the "Concentrations" tab, you enter the calculated total indoor air concentration from the first simulation.
For situations with a partial groundwater contamination below the building and possible health risks only due to exposure via inhalation (not via outdoor air or otherwise), you only have to perform the first step in the above mentioned approach.
 

last modified on 10/01/2019 - 10:18

FAQ Category: