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
Chesapeake Energy Corp,the Oklahoma-based firm is the No. 1 driller in Ohio.
Rig Count Interactive Map by Baker Hughes, an energy services company.
Shale Sheet Fracking, a Youngstown Vindicator blog.
The Ohio Environmental Council, a statewide eco-group based in Columbus.
Earthjustice, a national eco-group.
People's Oil and Gas Collaborative-Ohio, a grass-roots group in Northeast Ohio.
Concerned Citizens of Medina County, a grass-roots group.
No Frack Ohio, a Columbus-based grass-roots group.
Fracking: Gas Drilling's Environmental Threat by ProPublica, an online journalism site.
Pipeline, blog from Pittsburgh Post-Gazette on Marcellus shale drilling.
Allegheny Front, environmental public radio for Western Pennsylvania.