This is exactly why I asked why you will need 10 people to throw rubbish? It has nothing to do with your needs, it is about your perception of 10 people doing something, I asked why 10since you stated that number.
Visit the vicinity of Boon Lay Interchange, tell me if the trash bins are full. If they are not, there are sufficient trash bins. If the trash bins are full, your logic of insufficient trash bins might apply. I see a photo of a trash bin in one of the photos, it does not look like it is over flowing.
when a group packs up & leave (presumeably) to dispose the rubbish into bins its highly unlikely they single out (or in milder terms, volunteer) 1 to do just that, would be odd among friends. they walking into the interchange as you have suggested & chatting along the way before the day has ended would be most likely. why 10 you ask? that is figuratively speaking, as there are likely a larger number in the field, 10 is an estimate.
friends who work together, relax together & likely live together, yet single out (volunteer) 1 to clear the trash (in this case) is a very odd group of friends. very odd indeed...
with the litter scattered across the field & not in the bins yet, you just assumed there are enough bins? logic as you see it?