Can it be that you once generated wrong URLs (a bug or something). Google indexed at that time your page finding all those URL's. Since those URL are basically valid category URL they return a valid page and google keeps them in the database?
Try changing in SEO & URL your category route to:
{id}/{rewrite}
And the layered nav route to:
{id}/{rewrite}{/:selected_filters}
You category view is then reached via: <home>/34/evaporation_materials
The old routes are invalid, so Google gets real 404's on those pages.
But beware. It invalidates all your current category links, impacting your google ranking for those pages.
Rg,
Leo