I'm no expert, but I have installed a few drain fields and spetic tanks in my younger years working in construction. I'm with those who say the important thing is proximity of the water source in case the fire gets away. As far as harming the leach field, I can't imagine that. Years ago we put in lines with trenches about three or four feet deep with 6" of gravel below the drain tile and probably 1.5' of gravel above & covered with a vapor barier. I would assume that would be similar to yours. A fire burning branches, etc. wouldn't heat up the ground enough to affect the leach line. I currently have a septic system with the plastic Infiltrator system. Large trucks have driven over it, I've burned brush, branches, trimmings over it, & when I spread out the pile with my tractor, there isn't any effect more than an inch or so into the soil. I've been burning in the same spot for 12 years.

OK, good to know. That was part of my problem, was that I didn't know how deep the leach field is likely to be. There's a shallow depression in the ground, and earlier this year, the grass was always a little greener and taller there.

Not necessarily. It depends on how deep the water table is. They don't want to put leach pipes right above your well water source.

Don’t do it. The heat will melt the plastic and the methane will POP like you wouldn’t believe.
On the other hand you will be famous in the town forever.
Decisions.

Rule #1 of a drainfield: Never cover it up with anything. Evaporation up, not just downward drain, is a big part of the function of a leach field.

Source: https://www.cetaylorandsoninc.com/5-things-homeowners-should-know-about-their-septic-drain-field

One might argue that a burn pile doesn't cover up a leach field or drain field, but any compromise to the system can become very costly to fix. In my area, a cost to redo a leach field is upwards of $50k.

You can likely find a more ideal spot for your burn pile...

-Z

I believe you need to exercise your mansplaining skills. Seriously, the missus won’t accept your sage authority on the topic of leach fields? Who wears the pants :-)

If this involves driving on / across the line with a vehicle or tractor, the answer is no.

I'll tell you this much, if you and your wife can't agree on a suitable location, pretty soon it won't matter where the pile is, you will be in a burn ban and will have to do something else with it. Or let it sit, but I bet she isn't going for that either.

If it were me, I'd light it up today. I f she complains, show her this post, and tell her it was the last burn in that location, for now. Easier to ask for forgiveness later.

Whatever he does, we want to see it from space.