Previous method in StormTac Web of producing distributed acceptable load (kg/ha/year), for the watershed to the recipient, has meant that the recipient’s acceptable load (kg/year) has been distributed over the total area (ha) of the watershed area. The new method is based on the fact that the distributed acceptable load is instead based on the recipient’s treatment needs (kg/year), the total load on the recipient (kg/year) and the area of the watershed area (ha).

It is the pollution load via the drainage (such as stormwater and baseflow) that stormwater measures refer to and therefore the new calculation of distributed acceptable load (kg/ha/year) is based on the total load via only stormwater and baseflow from the watershed area, and does not include the part that comes as direct atmospheric deposition on the recipient surface and not as the part of the groundwater that flows directly into the recipient.

The improved function and description in the guide provides the opportunity to distribute the treatment needs to several actors (the Transport Administration, municipalities, operators, etc.). The distribution of the treatment needs is based on the amount of pollutant load the individual operator contributes to in the catchment area.