Televised ducts under slab floor. Ducts appear to be PVC ducts with metal fittings and connections that are allowing sand to enter into the system from outside the ducts. The plenum is also rusted with sand on the bottom. There appear to be water marks in the ducts but there was no standing water at the time of the inspection. Suggest spin cast mortaring the joints repairing the plenum then spray lining the system with Duct Armor duct lining material. Downspout an d gutters have been replaced but only on this unit. Other units on building are not. Downspouts on this unit are extended underground