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.
U.S. industries have injected more than 30 trillion gallons into rocks below ground in the past several decades, according to ProPublica.
The assumption is that the toxic waste is safe below ground and does not pose a threat to aquifers.
Reporter Abrahm Lustgarten found there are more than 680,000 underground waste and injection wells in 32 states including Ohio.
His long review of injection wells includes a review of more than 220,000 well inspection reports on file with government agencies.
From late 2007 to late 2010, one well integrity violation was issued for every six injection wells examined, he said. That's more than 17,000 violations nationally.
He looked at injection well problems in Ohio, Texas, Florida and Louisiana.
Click here to read his report.