I would imagine it's possible to create landfills in areas that are 'geological material sinks' (lay-person made-up term) - i.e. places where particulate matter

I would imagine it's possible to create landfills in areas that are 'geological material sinks' (lay-person made-up term) - i.e. places where particulate matter has a tendency to accumulate rather than diffuse elsewhere over time. Better to concentrate vast quantities of waste in isolated areas where it's relatively contained than let it pollute literally everywhere on earth.