When I worked for a supermarket market chain back in the 80's, the company bought a couple of independent stores. One only a year or so old and the other was maybe 20 years old. When surveying the mechanicals for a remodel at the the older one, I noted the store had a noticeable odor upon entering at the front.,,something that reminded me of a freshly mopped floor using Pine-Sol. When I got to the mezzanine above the meat room in the back where the main air handler was, I found an open access panel in the return air plenum. Inside, there were five or six air freshener sticks with lots of used ones scattered on the floor.
It turned out, later during the remodel work, the odor was indeed coming from the meat prep room and meat cooler area. There was a long-broken floor drain in the prep room which upon opening up led to what was a virtual cesspool of swirling maggots and rotted meat mixed in the sewage. In was as close as I (and others) ever came to puking on the spot. The cesspool had undermined the ground under the adjacent meat cooler too.
