I am at a farm where previous tenants left a non-biodegradable plastic film roughly 10-15 years ago. It is inconsistently spread over a few acres and was not discovered until we attempted plowing the fields. The fields are overgrown with weeds (grasses, thistles, small shrubs, etc.) about 1m tall and this growth has fragmented the plastic considerably (see image, left). The plastic must be removed in order for food to be safely grown there, and to meet the organic standards of the farm.
One issue that you've got is the area will be contaminated with fragments of plastic that are microscopic in size to large pieces and they will be at varying depths throughout the soil.
To most people that wouldn't be much of a problem, but for you, who wants to grow food with an organic certification it's going to be a major problem.
Setting fire to that land and burning the plastic with dried vegetation is not a option for you and your desired organic accreditation.
If you can't use the land for another purpose, such a site for new buildings, a parking lot for visitors, or a new roadway you may need to dig deeply to remove the affected soil, and more, and then import replacement soil from elsewhere.