Televised ducts under slab floor. Ducts are spiral wound plastic covered galvanized ducts that are showing signs of heavy rust and possible mold on plastic. There was dirt and mud in the larger ducts in the back of the house where ground water was entering the system at times of rains. Grading and downspouts should. Be addressed then the system should be spin cast mortared then spray lined with Duct Armor duct lining material.