Approximately 62% of municipal waste is placed in landfills. If the waste is dumped untreated, it can promote the proliferation of rats, flies, and other vermin, encourage growth of disease-carrying organisms, contaminate surface and underground water, scar the land, and preempt open space. An alternative method of solid waste disposal is the sanitary landfill, first employed in Fresno, Calif., in 1937: waste is spread in thin layers, each tamped compactly and covered by a layer of earth. While more expensive than open dumping, the sanitary landfill eliminates health hazards and permits reclamation of the site for construction, recreation, or other purposes. The chief drawbacks are that feasible locations are relatively rare and costly and that sites must be insulated from water resources to avoid polluting them (see water pollution). Both open dump and sanitary landfill disposal depend on the natural degradability of wastes for an ultimate return to normal earth conditions. Decay, however, takes time; buried paper, for example, can persist as long as 60 years. Many plastics and synthetic textiles do not degrade at all.