With only 6 to 18 inches to the water table, it probably isn't that the land doesn't drain it is more that it can not drain. Plant covers and what ever else you desire to grow and they most likely will grow fine. Lay down some
compost then cover with mulch and as these layers are taken into the soil it will improve. Roots improve the soil through their entire life cycle, decaying forest litter also improves the soil. If this land was reclaimed by mother earth as you state, the soil is not in such bad shape, after all, it became forest again so you know things will grow there.
In permaculture there is no "bad soil" there is soil that needs tender loving care. By careful use of the land to grow your desired plants, applying cover crops and composting and mulching, you will be stewarding the land back to really good health.