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Frequently Asked Questions

We are currently completing this page with an initial set of questions. This page will be continuously updated as we receive new requests via the S-Risk helpdesk.

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How to choose the appropriate soil type?

When defining the appropriate soil profile in S-Risk, it is important that the soil layer types you add on the Soil tab have soil properties that are as close as possible to the ones of the soil profile at your site. As a first, pragmatic approach, you can choose the soil types that provide you the best match regarding organic matter and clay content (these properties are visible in Tier 1).
In case the soil properties at your site deviate significantly from the ones available in the default database, it is recommended to switch to Tier 2 and to customize the selected soil layer types. In Tier 2, additional soil properties such as volumetric air content (θa), total soil porosity (θs) and volumetric water content (θw) become visible and editable. When using S-Risk FL/BRX and when site-specific information is not available, you can use Annex I of the FL/BRX technical guidance document to estimate the Tier 2 soil properties from more readily available soil information.
last modified on 10/04/2017 - 12:12

Why do RI (or ExCR) and CI results differ for volatile substances?

For volatile chemicals, there are a number of conditions which can result in a RI (or ExCR) which is more stringent than CIindoor air. Situations were CI is more stringent than RI (or ExCR) are explained in a separate FAQ.

  • RItotal ≠ RIinhalation although the only exposure route is inhalation
    For threshold effects, S-Risk also accounts for background exposure. RItotal reflects total local (through air) and total background (through air, drinking-water and food) exposure; RIinhalation reflects local and background exposure through inhalation only.
  • RIinhalation or ExCRinhalation leads to a more stringent result than CIindoor air and indoor exposure dominates inhalation exposure
    There are a number of reasons why this kind of results is obtained (typically in residential scenarios).
    • RIinhalation or ExCRinhalation takes into account the higher inhalation rate per unit of body weight of children relative to adults, whereas the CI value only compares concentrations in air,
    • RIinhalation or ExCRinhalation is calculated using a health-based value (Tolerable Concentration in Air), while CIindoor air is calculated using a legal limit (if available) or the same health-based value. If a legal limit is used, which is higher than the health-based value, CI results will be less stringent.

last modified on 09/09/2016 - 12:45

Why do mercury, copper, nickel, zinc and lead simulations sometimes give counterintuitive results?

For mercury compounds, copper, nickel and zinc, S-Risk adopts non-standard model equations for most plant uptake factors (the so-called BCFs or bioconcentration factors). For mercury compounds, copper and nickel, these BCF models include a discontinuity (jump) at a soil concentration equalling four times the background concentration of the chemical (official background concentrations in 2007; values can be found in the substance data sheets). For zinc, the BCF models include two jumps, namely at a soil concentration of 60 and 360 mg/kg dm. Also for lead, a discontinuity takes place (at a soil concentration of about 1000 mg/kg dm and more) due to the non-standard model used for the determination of the soil-water distribution coefficient Kd.

These jumps can sometimes be seen clearly in the graphs of the risk index (RI) versus soil concentration. For mercury compounds, copper and nickel, this typically occurs in scenarios with the intake via locally produced vegetables, meat and milk and/or eggs as an active pathway. For zinc, the graphs of scenarios with the intake via locally produced vegetables checked as active pathway might include discontinuities. For lead, a jump typically occurs in scenarios with the intake via locally produced meat and milk and/or eggs as an active pathway or where groundwater is used as drinking-water. The graph below presents the function discontinuity for the overall risk index (RI) for systemic effects of mercuric chloride versus soil concentration: the RI crosses the threshold value of 1 at two soil concentrations.

FAQ BCF Hg Ni - graph tab


The optimization algorithm currently used in S-Risk (i.e., from version 1.1.5 onwards) for application I and III will systematically find the higher critical soil concentration of the two concentrations shown in the graph above, i.e., the wrong/less stringent choice for a soil remediation value.& The basic principle in this situation is that the lowest soil concentration should be retained in your risk assessment. For these situations, S-Risk will always generate a clear warning message in the reports and advise you to double check your optimization result using the Graph tab.

last modified on 24/03/2017 - 9:54

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

How to account for background exposure when using measured concentrations in air, food/feed or drinking water?

last modified on 01/12/2016 - 09:19S-Risk FL/BRX takes into account background exposure in the risk characterization for threshold effects. For these effects, the risk is calculated using a TDI approach (see the Risk tab). Background exposures via food and drinking water are added to local oral exposure; background exposure via inhalation is added to local inhalation exposure. If you have measured concentrations, you should account for model background concentrations before entering values in S-Risk, in the following way:

  • Measured concentrations in outdoor or indoor air
    Subtract the background concentration used in S-Risk from the measured total air concentration. If the background concentration is higher than the measured concentration, a zero value (0) should be used as measured concentration. The chemical-specific background concentrations can be found in the substance data sheets (FL/BRX) or on the Exposure tab in the S-Risk model;
  • Measured concentrations in local food and feed
    No correction is needed. The measured value can be entered as such in S-Risk. S-Risk automatically accounts for the fraction of locally consumed food when calculating background intake from food;
  • Measured concentration in drinking water (i.e., the water that is consumed)
    If a concentration is filled in for the field “Drinking water” on the Concentrations tab, the calculated concentration in the final drinking water (i.e., the weighted average of the concentration in groundwater and supply water, whereby the weighting factor is the fraction groundwater in local consumption) is overwritten:
    • if there is no local groundwater consumption (i.e., only water from the water supply system is used):
      Subtract the background concentration used in S-Risk from the measured concentration in drinking-water. If the background concentration is higher than the measured concentration, a zero value (0) should be used as measured concentration. The chemical-specific background concentrations can be found in the substance data sheets or on the Exposure tab in the S-Risk model;
    • if there is 100% local groundwater consumption:
      In case of 100% local groundwater consumption, no correction for background is needed;
    • if there is partial local groundwater consumption:
      In case of partial local groundwater consumption, correction for background exposure is complex and is therefore approximated. It should be done for the water supply concentration and the groundwater concentration separately (as explained above). Then, the drinking water concentration should be calculated according to equation 26 in the S-Risk TGD . The chemical-specific background concentrations can be found in the substance data sheets or on the Exposure tab in the S-Risk model. The fraction local groundwater consumption is 0 by default, its value can be found on the Scenario tab.

In the case of non-threshold effects, background exposure is not added to local exposure. However, the above corrections are allowed as well, as the acceptable excess lifetime cancer risk is only applicable to local site contamination.

Overview of corrections for background exposure to be applied to measured concentrations:

Medium Correction for background exposure
Outdoor air Subtract S-Risk background concentration in outdoor air from measured value; value should be >= 0
Indoor air Subtract S-Risk background concentration in indoor air from measured value; value should be >= 0
Local food & feed Enter measured concentration without correction
Drinking water from water supply system Subtract S-Risk background concentration in drinking water from measured value; value should be >= 0
Drinking water from groundwater Enter measured concentration without correction
Drinking water partially from water supply system, partially from groundwater Approximate as explained above

last modified on 01/12/2016 - 09:19

How does switching land use affect the parameter values?

Within a simulation, it is possible to change the land use type of your scenario by selecting another land use on the Scenario tab.

When you do this, you have to keep in mind that the following parameter values will be reset to the corresponding land use defaults:

  • Scenario tab (parameters only visible in Tier 2):
    • time patterns on site (see Tables 35-43 in the FL/BRX and Tables 35-42 in the WAL version of the Technical Guidance Document (TGD))
    • soil & dust ingestion rates (see Tables 44-45 in the FL/BRX TGD and Tables 43-44 in the WAL TGD)
    • fraction of soil contributing to soil & dust ingestion (see Table 44 in the FL/BRX TGD and Table 43 in the WAL TGD)
    • fraction of groundwater used as drinking water (see Table 46 in the FL/BRX TGD and Table 45 in the WAL TGD)
  • Water tab:
    • enter / calculate groundwater concentration (gets reset to "Calculate groundwater concentration")
    • fraction of drinking water intake coming from site (only visible in Tier 2, see Table 46 in the FL/BRX TGD and Table 45 in the WAL TGD)
  • Outdoor air tab (parameters only visible in Tier 2):
    • terrain roughness length (see Table 47 in the FL/BRX TGD and Table 46 in the WAL TGD)
  • Indoor air tab:
    • building type (gets reset to "basement")
    • state of floor (gets reset to "gaps and holes")
    • basic air exchange rate for indoor space (only visible in Tier 2, see Table 15 in the FL/BRX and WAL TGD)
    • fraction of soil in indoor dust (only visible in Tier 2, see Table 47 in the FL/BRX TGD and Table 46 in the WAL TGD)
  • Exposure tab (parameters only visible in Tier 2):
    • food consumption rates for vegetables & animal products (see Tables 29-30 in the FL/BRX and WAL TGD)
    • fraction of local origin for vegetables & animal products (see Table 46 in the ​FL/BRX TGD and Table 45 in the WAL TGD)

last modified on 10/04/2017 - 12:19

How does S-Risk deal with concentrations exceeding solubility?

S-Risk deals with concentrations exceeding solubility in different ways, depending whether it relates to a soil or groundwater contamination.

It should be noted that in case of very high concentrations, approaching solubility, attention should be paid to the presence of non-aqueous phase liquids. You should consult applicable guidance documents in your region on how to deal with non-aqueous phase liquids in site assessment.

Soil concentrations

When you enter a soil concentration for an organic pollutant, S-Risk will limit the calculated concentration in soil pore water to the solubility of the chemical. You can find this value on the Chemical tab and in the substance data sheets. The concentration in soil pore water is used for the calculation of leaching to groundwater (if a groundwater concentration is not entered), volatilization to outdoor and indoor air, permeation through drinking water pipes and plant uptake (depending upon the type of plant uptake calculations). As S-Risk is not designed to calculate mobility of non-aqueous phase liquids in soil, limiting the pore water concentration to solubility is a conservative approach with regard to human health risk assessment, in most cases. The water solubility of chemicals in pure product (mixtures) is at maximum equal to the solubility of the chemical (assuming ideal behaviour). Keep in mind that permeation through drinking water pipes is potentially underestimated.

Groundwater concentrations

When you enter a groundwater concentration for an organic pollutant, S-Risk will generate a warning message if the entered concentration exceeds the solubility of the chemical:


The solubility value can be found on the Chemical tab and in the substance data sheets. You will, however, be able to continue data entry and run the calculations. S-Risk will use the filled-in groundwater concentration for further transfer (volatilization to outdoor and indoor air, permeation through drinking water pipes) and direct exposure (direct consumption of  groundwater as drinking water if selected as an exposure pathway, consumption of groundwater by animals if applicable) calculations. Using a groundwater concentration exceeding the solubility value will result in an overestimation of the soil air concentration and thus, in an overprediction of the transfer to outdoor and indoor air.

If inhalation from outdoor and/or indoor air are the only exposure pathways for groundwater, the solubility limit can be entered as groundwater concentration in a Tier 1 assessment. However, you should be aware that groundwater concentrations exceeding solubility point to a need for further evaluation of the data on groundwater quality in view of overall site assessment (not limited to human health risk assessment). 

last modified on 25/11/2015 - 13:40

Which parameters do I have to provide when adding a new chemical?

ou can add a new chemical by selecting and adding "(Blank chemical)" from the drop-down menu on the Chemical tab. Afterwards, under Tier 2, you have to fill in various chemical related parameters on the following tabs:

  • Chemical tab: Physico-chemical property data.
    Depending on the type of chemical (i.e., inorganic or organic), other parameters may be required.
  • Plants tab: Volumetric washout factor for particles, metabolization rate, photodegradation rate and transfer factors for vegetables and animal feed plants.
    These parameters should only be provided when you have selected at least one of the following exposure pathways on the Scenario tab: intake via locally produced vegetables, meat and milk or eggs. Default values are provided for the volumetric washout factor for particles, the metabolization rate and photodegradation rate. In case of an organic chemical, the transfer factors for vegetables and animal feed plants can also be calculated by the model.
  • Animals tab: Transfer factors to animal products.
    These factors should only be filled out when you have selected at least one of the following exposure pathways on the Scenario tab: intake via locally produced meat and milk or eggs. In case of an organic chemical, the transfer factors to meat and dairy products can also be calculated by the model.
  • Concentrations tab: Just as for built-in chemicals, you have to provide concentrations of the new chemical in all added soil layers and in groundwater (if this option is chosen on the Water tab). If relevant, pathway specific soil concentrations can also be filled in as well as concentrations in transfer media and animal related (background) concentrations.
  • Exposure tab: Background exposure via food, relative bioavailabilities, age specific weight factors, dermal exposure parameters and background concentrations.
    Default values are foreseen for the relative bioavailabilities and the age specific weight factors. Background exposure and concentration data need to be provided in case of a chemical with threshold effects (i.e., for which the risk is calculated using a TDI approach). Furthermore, the background concentrations in plants and animal products are only of significance in case you have a scenario with consumption of local food. In case of an organic chemical, dermal absorption from water can also be calculated by the model.
  • Risk tab: Toxicological reference values.
    Depending on the type of chemical (i.e., with threshold, non-threshold or pseudo-threshold effects), other parameters may be required.
  • Concentration limits tab: (Legal) concentration limits for transfer media.

The user manual (EN / NL) provides more information on how to fill in these fields.
last modified on 01/12/2016 - 09:28

Why can’t I customize the properties for copper, nickel, mercury, zinc or lead?

The metals copper, nickel, zinc, lead and the mercury compounds follow non-standard models for the calculation of Kd factors, pollutant uptake in plants and/or transfer to animal food products. These model exceptions were decided upon during the development of the Flemish soil remediation values, independent from the S-Risk development, and can be found in the substance data sheets (FL/BRX - WAL).

To avoid confusion with regard to the models used, these chemicals cannot be modified. If you would like to work with modified versions of these chemicals, you will need to configure them starting from the ‘Blank Chemical’ template available in the chemical list. In this case, you will also need to calculate the appropriate Kd factor, bioconcentration factor (BCF) and/or biotransfer factor (BTF) from the models given in the substance data sheets.

last modified on 10/04/2017 - 12:22

How to simulate the presence of a paved surface?

In case the soil on the site under study is paved, you can simulate the presence of a pavement (asphalt, concrete) by creating a top soil layer  on the Soil tab (the soil type of this layer does not matter), with a thickness corresponding to the real thickness of the pavement. The properties of that top layer should be modified as follows:

  • Switch to Tier 2 and customize the soil type;
  • Modify  the value for air-filled porosity θa according to the type of pavement (Table 10 of the Flemish/Brussels and Walloon version of the Technical Guidance Document can be used as a guide, but you should check the validity of the data for your conditions);
  • Change the value for total porosity θs to 2 times the value of the air-filled porosity θa;
  • Change the value for water-filled porosity θw to 0.

The remaining soil properties do not need to be changed and certainly does not have to be set to 0 (which should lead to erroneous results).

On the Indoor air tab, make sure that the paved top layer is not involved in the sub-building soil profile (i.e., the depth of the floor of the concrete slab, the crawl space or the basement floor below the soil surface should be equal to or bigger than the thickness of the paved top layer).

On the Concentrations tab, fill in a concentration of 0 mg/kg dm for the paved top layer.

You should not use the above approach if the pavement is of bad quality (i.e., with cracks and holes), if the contaminated area is only partially paved, or if the pavement is of an open type (e.g., to allow rainwater infiltration).

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 (thresholdnon-threshold and pseudo-threshold). A further distinction is made between systemic and local effects.

The toxicological information on the chemical determines which types of effect are considered. If a certain type of effect is not relevant for the chemical, the field(s) in the report for that type of effect will be empty. The risk metric to be retained for risk decisions and the cut-off value (value above which one should decide that there is a human health risk) for each risk metric is given in the table below.

Type of effect Risk metric Cut-off value
(Flemish soil remediation Decree)
Systemic Highest RItotal of the reported age groups RI = 1
Local Highest RI (oral or inhalation) of the reported age groups RI = 1
Systemic ExCRtotal for lifetime exposure ExCR = 1x10-5
Local ExCR (oral or inhalation) for lifetime exposure ExCR = 1x10-5
Systemic pRItotal for lifetime exposure pRI = 1
Local pRI (oral or inhalation) for lifetime exposure pRI = 1

Type of effect Risk metric Cut-off value
(Flemish soil remediation Decree) Threshold Systemic Highest RItotal of the reported age groups RI = 1 Local Highest RI (oral or inhalation) of the reported age groups RI = 1 Non-threshold Systemic ExCRtotal for lifetime exposure ExCR = 1x10-5 Local ExCR (oral or inhalation) for lifetime exposure ExCR = 1x10-5Pseudo-threshold Systemic pRItotal for lifetime exposure pRI = 1 Local pRI (oral or inhalation) for lifetime exposure pRI = 1

The risk indices (RI or pRI) and the excess cancer risk values (ExCR) are based on the calculated exposure to the contamination. While calculating this exposure, S-Risk takes into account all scenario details (land use, time expenditure, …) the user has entered. Calculated exposures are then divided by their toxicological threshold values to obtain the final (p)RI values or are multiplied by the unit risk/slope factor to obtain the ExCR values.

Application II also reports concentration indices (CI). This is the case if legal limits or toxicological reference values are available for the environmental compartment under consideration (water, air, food products). The cut-off value for CI results is set at 1.

CI values are calculated by comparing the chemical concentration in a specific environmental compartment with the concentration limit for that compartment. These limit values do not take into account any scenario details the user has entered, and often suppose a full-time exposure of 24 hours/day, 365 days/year. This may or may not correspond to the real site scenario. Concluding:

  • A (p)RI value > 1 or an ExCR > 1×10-5 represents a risk;
  • A CI value > 1 may or may not imply a risk, depending on the exposure conditions or the type of limit value used for calculating the CI.

The way these results are further interpreted with regard to site remediation or management depends upon the procedures available in your region. For Flanders, further guidance is given in the procedures for risk assessment and detailed site investigation.

last modified on 10/06/2015 - 17:00

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.

However, simulation results show that in cases where diffusion (concentration gradient drives vapour intrusion) is dominant over convection (pressure difference drives vapour intrusion), the default settings for floor quality result in higher indoor air concentrations for the 'intact floor'. Diffusion processes will typically start to dominate over convection in less permeable soil types and in case of deep contamination.  The cause for this counterintuivitive result is the difference between the concepts for the floor type options: for 'intact floor', Volasoil considers diffusion to occur over the whole floor area while for a 'gaps & holes' floor, diffusion is only considered to occur from the gaps & holes themselves, which is only a small fraction of the whole floor area.

We recommend to use 'gaps and holes' as the default setting. Except in situations where it is clear that the floor meets the condition of intact floor (new buildings, no gaps or seems, coating, ...), the option 'intact floor' can be chosen in association with values for air permeability and air-filled porosity corresponding with good or very good quality. Default values can be found in the Technical Guidance Document (table 10 in FL/BRX and WAL version).

last modified on 10/04/2017 - 12:24

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:

  • If there is water in the basement or the basement walls or floors are moist, there is a high-risk situation for indoor air volatilisation: measuring indoor air concentrations is the preferred option.
  • If the basement is constructed to avoid entrance of moist, the floor and walls most probably restrict vapour intrusion. In case of modelling, you probably have to adapt the floor and wall quality parameter values in S-Risk. We do recommend however to verify with indoor air measurements.

In case of future projects, modelling vapour intrusion should be in line with construction requirements to avoid moist and vapour intrusion.

In some situations, the basement floor is situated below groundwater level (as shown in situation ① of the scheme). Currently, S-Risk is lacking the models for calculations in this situation, and consequently does not allow for a basement depth below groundwater level.

To cope with this situation, you can follow a workaround solution in which you enter the groundwater concentration as a 'surrogate' soil concentration, Cartificial , using an artificial soil layer. A crucial step is the calculation of a surrogate soil concentration Cartificial corresponding to the groundwater concentration Cgw. To make the calculation easier,  we have made available an Excel tool that you can download here.

The steps in the workaround are as follows:

  • On the Soil tab, enter a groundwater level that is situated below the depth of the basement. Then, fill in the soil profile corresponding to the site information, but create an additional soil layer between the effective depth of the groundwater table (site information) and the value for groundwater table depth you entered in S-Risk.
    This is illustrated in step ‚② of the scheme. The properties of this artificial soil layer are not critical, but you need the information for the calculation tool. The properties of the artificial soil layer in S-Risk and in the calculation tool need to be exactly the same!
  • On the Water tab, choose the option of entering a groundwater concentration.
  • Use the calculation tool to calculate the surrogate soil concentration, Cartificial. The calculation tool contains detailed guidance on how to do so (see step ③ƒ in the scheme).
  • On the Concentration tab, enter the soil concentrations corresponding to the site information for the effective soil layers. Enter the surrogate soil concentration Cartificial from the calculation tool as the soil concentration for the artificial soil layer. Set the groundwater concentration Cgw equal to zero.
  • Run your simulation (see step ④„).
Kelder in grondwater

If you would need a remediation value for the groundwater layer, you can use the above type of simulation. It will give you a surrogate soil remedation value for the artificial soil layer. The groundwater remediation value then corresponds to the pore water concentration in equilibrium with the calculated soil concentration, which you can read from the extended report of application II).

last modified on 10/06/2015 - 16:44

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.

This optimization is run for a concentration range of 0 - 106 mg/kg dm for soil and 0-109 µg/L for groundwater. The efficiency of this optimization procedure not only depends on the algorithm itself, but more importantly, on the complexity of the relation between soil/groundwater concentration and risk index. For instance, when in application III, several soil layers or (a) soil layer(s) in combination with an entered groundwater concentration are used, the layer determining the risk can shift while the concentration is modified during optimization, and in certain cases the optimization algorithm can be hampered in finding the correct critical concentration. In other cases, the calculated risk may be lower or higher than the critical threshold for all soil concentrations in the preset concentration range. In these cases, a critical soil concentration cannot be found by S-Risk as it does not exist.

The situations above are flagged by S-Risk, using one of the following warning messages:

  • “The index is lower than the critical level for all realistic concentrations.”
    This message appears when S-Risk could not find a concentration within the considered realistic range that causes a risk. The critical concentration will be set to 106 mg/kg dm for soil layers or to 109 µg/L for groundwater.
  • “The index exceeds the critical level for all realistic concentrations.”
    This message appears when the layer to be optimized always involves a risk or another layer than the optimized one is determining the risk. The critical concentration will be set to 0 for both soil and groundwater.
  • “This substance uses non-standard calculation models. Double check the result using the Graph tab.”
    This message appears always for the chemical substances Cu, Ni, Hg, Zn and Pb as – mathematically speaking – multiple critical concentrations could be found due to discontinuities or a non-monotonous behavior of the relation between soil/groundwater concentration and threshold risk level and the optimization algorithm does not necessarily finds the lowest concentration. You should use the Graph tab for a concentration range between 0 and the critical concentration reported by the optimization algorithm to check whether there is a lower critical concentration (the lowest should be used in your risk assessment).
  • “An unknown error has occurred while searching for the critical concentration. Use the Graph tab to plot the index in function of the concentration in the optimized layer.”
    When this message appears, it is recommended to check if all necessary input data were provided correctly. When the Graph tab also does not give any explanation, it is best to contact the helpdesk.

last modified on 09/09/2016 - 12:17

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.

During the development of the S-Risk model, this inconsistency was acknowledged and discussed in detail. Together with the S-Risk steering committee (OVAM, VEB), the decision was made to leave the model as-is, since outdoor air concentrations rarely form the key issue in most soil investigations.

Due to this inconsistency, you may sometimes encounter strange results from S-Risk when comparing simulations with "buried" versus topsoil layers. An example can be seen in this picture:


This picture shows the value of the calculated critical soil concentration (Y axis), varying with the depth of an uncontaminated layer (X axis) covering the polluted layer. When the covering layer disappears (x → 0m), the soil-to-outdoor-air model inconsistency results in an unexpectedly high critical soil concentration.

last modified on 24/11/2014 - 08:59

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. So, the soil layer-specific concentrations resulting from volatilization are not summed together, nor are the concentrations resulting from volatilization from soil and groundwater. Instead, it is the maximum contributing layer that determines the final exposure & risk.
In application III, this poses a problem. Since S-Risk only calculates critical concentrations for one single layer at a time, it can not provide guidance when multiple layers significantly contribute to the risk together. In these cases, it is advisable to calculate critical concentrations for each layer separately, ignoring the contamination in the other contributing layers. This is explained in more detail in the OVAM guidelines for soil remediation experts, see https://www.ovam.be/sites/default/files/21-02-2014_Richtlijnen_BSD.pdf (section on "Locatiespecifieke saneringsdoelstellingen voor bodem en voor grondwater").
last modified on 24/11/2014 - 08:59

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:

  • convert the measured concentration of the submerged soil layer to an equivalent pore water concentration. This can be done:
    • based on equations 17/18/19 of the Flemish/Brussels and Walloon version of the Technical Guidance Document, or
    • based on the approximate formula Cporewater [mg/m³] = Csoil [mg/kg] × 1000 / Kd [l/kg].
      The calculation of the Kd depends on the type of chemical. More information is given in the Technical Guidance Document - chapter 2.2.1: Kd values.
  • enter the calculated pore water concentration in S-Risk as a measured groundwater concentration (using the "Water" and "Concentrations" tabs)

If you have an actual concentration measurement for groundwater, use that value for the measured groundwater concentration.

last modified on 10/04/2017 - 12:26

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:

  • As a worst case, first fill in the basement air concentration as if it was the indoor air concentration.
  • Assume a building with a crawl space ("crawlspace" option on the "Indoor" tab) and set the floor quality parameter fof (fraction of openings in the floor between crawl space and indoor air) at bad (1×10-4) or very bad quality (2×10-4). Proposed parameter values according to floor quality are given in the TGD. Then, fill in the basement air concentration as a crawl space concentration in the "Concentrations" tab.

last modified on ​24/11/2014 - 08:59

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.

  1. Select the "basement" option in the "Indoor" tab, enter dimensions for the basement equal to the effective crawl space dimensions, and set the volume of the indoor space to 0 m³ and the basic air exchange rate for indoor space to 19.2 d-1 (default value for a crawl space);
  2. Perform a simulation run and note the resulting indoor air concentration (i.e., “indoor air concentration from volatilization (mg/m³)” within the section “Building: General” of the detailed report);
  3. In a second run, select "crawl space" in the "Indoor" tab and enter the real dimension for crawl space and indoor building volume (groundfloor) as appropriate for the site;
  4. The indoor air concentration from the first run can now be filled in as a measured "Crawl space" concentration in the "Concentrations" tab.

last modified on 25/11/2016 - 11:37

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How to use...

How to use the simulations overview table ?

Sorting :

The table contains several columns which can be sorted on by clicking with your mouse on the column header. You can sort ascending or descending by clicking multiple times on the same column header.

Filtering :

Some columns contain also a filter input field in the column header : you can input part of the text to which corresponding row fields must be conforming with before they are made visible. You can e.g. use the 'label' field to group multiple simulations together and afterwards this group can be found back by giving the filter field in the label column part of the group name.

last modified on 24/11/2014 - 08:59

Why is field X or field Y not editable?

The accessibility/editability of fields in the interface can be determined by several configuration factors:

  • the configuration of exposure routes on the Scenario tab: for instance, chicken-related parameters on the Animals tab will not be editable when the "Intake via locally produced meat & milk" route is disabled.
  • wether or not a related item is customized or not: for instance, plant & risk parameters are not editable if your chemical is NOT customized. Or, data for ingestion rates in the Scenario tab are NOT editable when the landuse is not customized.

last modified on 24/11/2014 - 08:59

What are the browser or network requirements for running S-Risk?

S-Risk is completely web based and operates fully inside of your browser. The only requirement for running S-Risk is a recent browser:

  • Google Chrome, Mozilla Firefox
    These browsers have long supported all browser features used by S-Risk and do not give any problems running S-Risk. Depending on the settings and/or version of the Google Chrome browser used, the print preview of the online result summary might not be complete, i.e. does not show all pages.
  • Internet Explorer
    S-Risk usage in Internet Explorer 9 or higher should not give any problems except that the online result summary may not always load when it should. Internet Explorer 8 does not support the graphical simulation overview (in the "Simulation summary" panel), but should otherwise run all S-Risk functionality normally. Internet Explorer 7 and earlier are not supported.
  • Safari 
    We have not tested S-Risk functionality in Safari, and hence, can not give any guarantees that all S-Risk functionality works without problems.

S-Risk uses the standard HTTP and HTTPS network ports for client-server communication, so in most cases, there is no need for special network or firewall configurations.

last modified on 04/12/2017 - 12:10

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Licensing & registration

How do I order additional S-Risk user accounts if I already have a license?

When you ordered the S-Risk license, you should have received an email with your S-Risk license details. This mail contains a link labelled "Your personal link", which gives you access to our webpage for ordering additional S-Risk accounts.
If you should have lost this email, please contact the S-Risk helpdesk so we can resend it to you.
last modified on 24/11/2014 - 08:59

S-Risk will be transferred from VITO to SPAQuE in 2023. What are the impliciations?

Based on a cooperation agreement signed with the 4 co-owners of S-RISK® : the Walloon Region, OVAM, Brussels-environment and the Grand-Duchy of Luxembourg, SPAQuE will take over, in the beginning of 2023, the management and development of S-RISK®, previously developed by VITO.

SPAQuE and VITO are cooperating on improving the S-RISK® application and preparing the transfer to SPAQuE. We have the ambition to make this transition as smooth as possible, not affecting previous or current work of the soil experts.

More information will follow in October, and meanwhile, answers to your questions will be answered as complete as possible on the S-RISK® FAQ. It is agreed that no new licenses need to be bought, and that yearly maintenance fees will be organized by SPAQuE in 2023.

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Problem solving...

Why does my simulation take so long to calculate?

The amount of time taken by S-Risk for calculating results is determined by several factors: (i) the application type, (ii) the number of chemicals, (iii) the number of risk endpoints, (iv) reading and saving data and (v) the calculation queueing procedure.

i) The application type
There is a fundamental difference in the way S-Risk performs calculations for Application II versus Application I & III simulations. The S-Risk model, in essence, is designed to take soil or groundwater concentration measurements as input and calculate human health risks as output. That is exactly what happens in application II:  a forward calculation that only needs to be executed once to retrieve exact results.
Applications I and III, however, perform the reverse operation: they calculate soil or groundwater concentrations corresponding to a pre-defined risk level. This implies a backward calculation of the model, and in mathematical terms, this translates to a so-called optimization procedure. Since the core S-Risk model can only calculate forward, i.e., from soil concentrations to risks, the desired concentration value needs to be determined in an iterative manner: the S-Risk model is run repeatedly with varying input soil concentrations.  The algorithm varies these concentration values itself, searching for the concentration that causes the risk to be equal to the pre-defined level. Finding this value can take 30 to 40 iterations, causing applications I & III simulations to take a lot longer to complete than application II simulations.

ii) The number of chemicals
A significant part of the S-Risk model calculations needs to be executed for every chemical added to the simulation. The more chemicals are present in a simulation, the longer calculation times are to be expected.

iii) The number of risk endpoints
For a single chemical, S-Risk calculates all possible risk and concentration indexes. This means that the calculation for a chemical with lots of toxicological reference values (e.g., Cadmium) takes longer than the calculation for a chemical with only a few toxicological reference values.

iv) Reading and saving data
Before any calculation can start on the S-Risk calculation server, the server first needs to retrieve the input data from the database server. After calculating results, the newly found values also have to be saved (written) back to the database server. These read/write operations typically take some time, as S-Risk simulations hold quite a lot of information in the form of input parameters, intermediate results and output results. These read/write operations also take longer when more chemicals are involved in the simulation.

v) The calculation queueing procedure
The number of calculation servers behind S-Risk is finite, and every calculation server processes one simulation at a time. This means that on busy moments with lots of customers working on S-Risk simulations, it is possible that all calculation servers are busy. In that case, the next simulation started (by any customer) ends up on a waiting queue, until one of the calculation servers becomes available for a new calculation. Currently, S-Risk has 6 calculation servers available to distribute the simulation workload. This number can be easily revised and expanded as our customer base grows. There are a few simple rules that determine which simulation is run:

  • Our basic principle is FIFO: first-in-first-out. If you are the first to submit a simulation, and a calculation server is available, your simulation will be started first;
  • The number of simultaneous simulations per account is limited to 2. If you start a 3rd calculation, and already have 2 simulations that are running, the 3rd simulation will be automatically moved to the waiting queue. This way, no single customer can block the calculation capacity for other customers;
  • If there are more than 6 simulations in the waiting queue, new requests for calculations will be cancelled. In this case, S-Risk will show you a warning message that the servers are too busy. Try again at a later time.

last modified on 28/09/2016 - 14:18

Why can't we use special characters in the simulation name?

S-Risk uses the simulation name for generating the file name of the report file. The transfer of this file via the website (over HTTP protocol) doesn't always correctly handle filenames with special characters, making the report unavailable for the user. For this reason, the use of special characters in simulation names should be avoided.
last modified on 24/11/2014 - 08:59

What do I do if S-Risk seems to be hanging?

In some cases, it's possible that the S-Risk application seems to be hanging. This is possible in case of bad internet connectivity or high load on the S-Risk server.
In these cases, it's best to refresh the browser page to get S-Risk working again, using the Refresh button on your browser or the F5 key. It's possible that you will have to re-enter the non-saved information in the last selected tab before refresh.
NOTE: closing your browser in this case will result in the "Maximum sessions of 1 for this principal exceeded" error, as described in this FAQ.
last modified on 06/07/2016 - 09:46

Why can't I login anymore? What does "Maximum sessions of 1 for this principal exceeded" mean?

The S-Risk login system is designed to allow only one simultaneous login session per account. A consequence of this is that S-Risk requires you to explicitly log out of the application using the user menu's "Logout" command on the upper right.
If you do not log out like this, for example, by simply closing the browser during an S-Risk session, the S-Risk server will maintain your login session for half an hour. Logging in again during this period causes the error "Maximum sessions of 1 for this principal exceeded". If this occurs, try logging in again after half an hour.
last modified on 24/11/2014 - 08:59