Underground injection wells
Steel- and concrete-encased shafts into which hazardous waste is deposited by force and under pressure.
Injection wells are widely considered to be the best method for disposal of treated waste water. Unlike outfalls or other direct disposal techniques, injection wells utilize the earth as a filter to further clean the treated wastewater before it reaches the receiving water. This method of waste water disposal also serves to spread the injectate over a wide area, further decreasing environmental impacts.
Critics of waste water injection wells cite concerns relating to the injectate polluting receiving waters. Most environmental engineering professionals, however, consider waste water treatment followed by disposal through injection wells to be the most cost effective and environmentally responsible method of waste water treatment. The only known alternatives to injection wells are direct discharge of treated waste water to receiving waters or utilization of the treated water for irrigation. Direct discharge does not disperse the water over a wide area; the environmental impact is focused on a particular segment of a river and its downstream reaches, or on a coastal waterbody. Extensive irrigation is often prohibitively expensive and requires ongoing maintenance and large electricity usage