From the OSC image, I can see that the sand is not really processed/filtered there, but is accumulated to be sold to whoever want to buy to build house etc. Any proper that for this amenity?

Suggestion for proper tags for this amenity? This is the site where sand that mined/extracted from river bed by using dredges is purified, filtered and processed to separate smaller and larger sand.

Done. Thanks a lot, Bryce.

It is a workshop for repairing motorcycles only, not for bicycles or cars. And not a self-service workshop. The workshop is operated by a group of foremen. Or, should I tag the node with other amenity attribute?