Injection well

An injection well is a device that places fluid deep underground into porous rock formations, such as sandstone or limestone, or into or below the shallow soil layer.

[1] The U.S. Environmental Protection Agency (EPA) defines an injection well as "a bored, drilled, or driven shaft, or a dug hole that is deeper than it is wide, or an improved sinkhole, or a subsurface fluid distribution system".

This method of wastewater disposal also serves to spread the injectate over a wide area, further decreasing environmental impacts.

[citation needed] In the United States, there are about 800 deep injection waste disposal wells used by industries such as chemical manufacturers, petroleum refineries, food producers and municipal wastewater plants.

It is argued that the impacts of some injected wastes in groundwater is not fully understood, and that the science and regulatory agencies have not kept up with the rapid expansion of disposal practices in US, where there are over 680,000 wells as of 2012.

Extensive irrigation is not typical in areas where the produced water tends to be salty,[5] and this practice is often prohibitively expensive and requires ongoing maintenance and large electricity usage.

After some twenty years, it was sued by environmental groups after multiple studies showed that more than half the injectate was appearing in nearby coastal waters.

A 2001 consent decree required the county to obtain a water quality certification from the Hawaii Department of Health, which it failed to do until 2010, after the suit was filed.

Steam, carbon dioxide, water, and other substances can be injected into an oil-producing unit in order to maintain reservoir pressure, heat the oil or lower its viscosity, allowing it to flow to a producing well nearby.

Complex hydrocarbons and other contaminants trapped in soil and otherwise inaccessible can be broken down by ozone, a highly reactive gas, often with greater cost-effectiveness than could be had by digging out the affected area.

Class II wells are used for the injection of fluids associated with oil and gas production, including waste from hydraulic fracturing.

Class III wells are used for the injection of fluids used in mineral solution mining beneath underground sources of drinking water.

USGS scientists have found that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells.