Swan1172:I assume you are trying to make a point about the potential for contamination of the air due to the four-wheeler running. Isn't that what the filters on the compressors are for?
I have my own compressor and make it a point to put the intake away from any fumes. Yes, there are filters, but those filters aren't cheap and keeping them near exhaust fumes means they need to be replaced more often. But if these people aren't that knowledgeable about scuba, they probably aren't testing the air very often and are just changing the filters on a regular schedule. I wouldn't get air from them.