Septic smell -- new system

I just had a septic system -- 1500 gallon tank, leach field -- installed on a 200+ year old farmhouse. The prior "system" was a pipe going out into a field. There is a 2" cast iron vent on the main line that goes out to the tank, and all of the sinks and tubs are trapped correctly. The toilet is also installed correctly, and the wax seal seems to be intact.

I'm getting intermittent septic smells in the basement and outside the house. I definitely smell septic smells from the vent over the leach field. I've run a hose down the vent stack to make sure that it's not plugged and it seems fine.

The vent stack is next to a dormer and so the roofline is roughly 6' higher than the top of the stack. I'm planning on extending that stack higher today to see if that makes a difference, but was also wondering if anyone here had any suggestions.

And isn't it wrong to have septic smells coming from the leach field vent? Isn't that supposed to be more of an intake vent, for fresh air to go in and push the lighter-than air toxic gasses up and out through the system via the roof vent?

(Of course, the plumber who I've consulted said it must be a septic problem and that I should call the septic installer. The septic installer said it's a plumbing problem and i should call the plumber....)

Thanks.

My own leach field is vented, and sometimes there is an odor at ground level rather than above the roof of the house. Maybe temperature and humidity affect that. I have heard there are charcoal filters for stopping that odor, but I have yet to actually ever try one.

My guess is that your septic system and plumbing are both fine, but I could be wrong.

Sounds like the perfect place to do a smoke test...

Smoke Testing