Explanation of injection wells
Injection wells can be developed from a formerly producing gas or oil well, an exploratory well or drilled specifically for underground disposal.
They are drilled into porous rock formations far below aquifers to a depth of 4,000 to 13,000 feet. The rock formation is always below an impermeable layer of rock or clay to ensure that injected fluids remain in the injection zone.
Experts note that drinking water is much closer to the surface, far away from the injection zones.
The injection wells require at least three layers of steel casing and cement to ensure that drinking-water aquifers are protected.
Injected wastes generally are high in dissolved solids and contain sodium chloride, calcium and magnesium, plus toxic chemicals from the drilling process and low levels of naturally occurring radioactive materials and heavy metals from the underground rock.
Traces of barium, zinc, cadmium, chromium, cobalt, copper, lead, mercury and nickel are also commonly found in brine.
— Bob Downing