90's City Dump Fieldtrip Mystery

Posting this on the off chance that someone knows the answer to this question!

When I was in elementary school in the late-90's we took a field trip to the Hartland Landfill. During that time I remember seeing/hearing this seagull-scaring loud noise type device that sounded (in my memory) like a shotgun blast. It went off on a timer from what I recall, and it scared the bejesus out everyone in my class.

Does anyone have any idea what that thing was? They might still use it at the dump today - I can't imagine bird scaring technology has advanced enough for an overhaul. I originally thought it was an actual gun, but then upon thinking about it more realized that would be bonkers.

If any knowledgeable dump people please could weigh in -- I would very much apperciate it!