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I'm puzzled by the term "poistotaso" in the following context (from a document about construction work standards):

"
Poistotaso on materiaalin poistotason muodostama maapohja. Poistotaso määräytyy suunnitelma-asiakirjoihin merkittyjen teoreettisten rajapintojen mukaan.
"

I've found several references to "poistotaso" elsewhere, but in all other cases I've seen, it refers to a rate, degree, or similar property: e.g. "pölyn poistotaso" is the percentage of dust that is removed using a given method, over a given period of time, etc.

By contrast, in the above definition, "poistotaso" seems to refer to an actual physical object or site ("maapohja").

Does anyone have a handle on what the author of that quote had in mind with "poistotaso"?

Thanks