Q.Weeds In Top Soil ?
Lawn Reno, lawn killed off with round up, all dead sod removed, nothing growing, tilled 6” base, added 15 yrs more to he approx 1500;2q ft lawn. Contoured, rolled, starter fertilizer added with new Seed. Used Scott’s bluegrass/ sunny mix with water technology for drought conditions. Lawn came up looked good in first 10 days. A week latter it was completely taken over by crab grass. I never had this weed or a lawn in such bad condition. My old lawn was far better. I cannot help but sate that the top soil must have been full of weed seeds. Probably the dead grassy stuff m6 experienced landscaper had never seen before.

Certified GKH Gardening Expert
Unfortunately, you may have to start over! Solarizing large swaths of land can be difficult, but not impossible. This will be a good way to go about killing off the seeds, and roots.
This article will help you to solarize soil: