Smell the Gasoline

Today’s experiment is of an environmental nature. It has to do with the gasoline smell that wafts out of the sewer grates on NE 16th Ave and NE Buchannan St in Minneapolis. I often walk my dog near there, as it borders on the Northeast Athletic Fields, a nice open park.
So far I have observed:
The smell is a gasoline or diesel fuel smell.
The smell is strongest when it is coldest out. The smell is strongest at NE 16th Ave and NE Buchannan, but also it is detectable at 16th and Lincoln and at 17th and Pierce. I couldn’t smell anything at 18th and Buchannan, but that is on a busier intersection and I felt a little weird kneeling down to smell the gutter.
On cold days, there is more steam coming out of the grate at 16th and Buchannan than anywhere else in the neighborhood.
There is an old elementary school at the corner of 16th and Buchannan.
The old school is heated by natural gas. I walked around the building and could hear the natural gas meter’s familiar whine.
What I have done :
Last December: I called a Hennepin county (or was it the city of Minneapolis?) agency for environmental protection. Gasoline in the sewer wasn’t their juristdiction but they seemed concerned and recommended that I call 911.
I called 911 and they said call the city Sewer department and even gave me the phone number.
The sewer department said “They’d look into it”. Unfortunately, they never asked for my name so they’re not going to tell me what they discover (if anything).
Today : I got online and emailed the Minnesota Pollution Control Agency. They emailed back and seemed concerned and suggested I call the fire dept. I related the story about calling 911 already and haven’t yet heard from them again.
My Hypotheses
The school is gas heated but still uses radiators. For some reason, they waste some of the hot water into the storm sewer system. That explains why the grates at 16th and Buchannan steam so much more than other grates.
Gasoline is volatile at warmer temperatures. The hot waste water from the school causes the gasoline in the sewer to warm up making it easier to smell at that intersection.
The smell is stronger on cold days because the temperature inversion — the cold air makes the hot air in the sewer rise faster. That brings the smell out into the air more readily.
There is a gas station only four blocks away, up hill from 16th and Buchannan.
Conclusions:
If my hypothesis about the warming of the storm sewer at 16th and Buchannan is correct, then the fact that the smell is strongest there does NOT indicate that the source of the pollution is there. The cold gasoline could be running down the storm sewer for many blocks and isn’t detectable by my nose because it isn’t getting warmed up.
There are some sources of error in this experiment. I already cited the socially induced error to my sampling method (being embarrased to sniff the gutter in front of traffic on 18th). Other factors include: My nose got stuffed up after too much sniffing, so I might not have been able to smell as well by the end of the walk. I don’t know how the storm sewers are connected together; I might be sniffing the wrong grates as I migrate away from 16th and Buchannan.
I’ll let you know if I find out any more about this study.