There are three main disposal methods for hazardous waste. One is landfills. Des

There are three primary means of hazardous waste disposal in the United States and most other developed countries: landfills, surface impoundments, and injection wells. Secure landfills store hazardous waste so that it is isolated from people, wildlife, and ecosystems. The standards for landfills that receive hazardous waste are higher than those of ordinary sanitary landfills. They must have several impervious liners and leachate removal systems and must be located far from aquifers. Another method for storing hazardous waste, particularly liquid hazardous waste or waste in dissolved form, is in ponds or surface impoundments. To create a surface impoundment, a shallow depression is dug and lined with plastic or an impervious material such as clay. Water containing small amounts of hazardous waste is placed in the pond and allowed to evaporate, eventually leaving a residue of solid hazardous waste on the bottom. The dry material is removed and transported elsewhere for permanent disposal. Surface impoundments may leak waste and some toxic material may evaporate, blow away, or travel in floodwater to surrounding areas. Therefore, impoundments are usually used only for temporary storage. The third disposal method is deep?well injection. In this long?term disposal method, a well is drilled deep beneath an area's water table. The well must reach below an impervious soil layer and must enter into porous rock. Wastes are injected into the well with the idea that they will be absorbed into the porous rock and remain deep underground, isolated from groundwater and human contact. Sometimes wells become corroded and leak waste into soil and aquifers.