[Green]

I would honestly just break up the soil and water it to displace the herbicide...and take the risk of bringing up seeds. My reasoning is unless I had a low spot, adding the amount of new soil necessary would probably result in a high spot. Let alone whether the seed would want to root below the new soil if the herbicide is still there below it. Plus, adding new soil is a risk in itself...could have weed seeds, jumping worm eggs, etc.

 

[Green]

Green - if the OP only has a few isolated spots, could he pre-germinate away from the pre-M herbicide that is in the yard, then spread the germinated seed with the germinating medium into those locations?

Yeah, sure. But is that going to help it establish good roots going through the layer where the herbicide is?

 

[Green]

How can you estimate where is that barrier, at what depth? Does it depend on how much water went down after applying pre-emergent? (I find it this topic a bit confusing also as a beginner) if the product is in the soil, I would think just disturbing it won't change much unless you replace the soil. Or does the little roots are able to like avoid the product in the soil and choose paths that don't contain pre-emergent active ingredient?

If it really creates a invisible barrier and the depth is variable, I can see how pre-emergent could be damagable for even like 1-2 year old grass if the product go deep enough, too much applied or mis-applied (I guess)

We're going to have to delve into the chemistry of how it works. Unless someone already knows how it works, this might take a while for everyone to learn. We might have to contact a manufacturer and get a chemist to answer some questions in order to understand this properly. I'm not going to speculate or regurgitate what I've heard from some of the pros on here like Matt M./Rey I./Ryan D., since I don't have this type of information. I'm sure someone else will, though...people usually do that on here (drives me crazy, but they do it).