Michelle Salvini (left) and Terri DiCarlo take a break from work outside the Cornerstone Care clinic in Burgettstown, Pa. Mysterious fumes have repeatedly sickened clinic staffers, forcing them to evacuate the building several times. Maggie Starbard/NPR hide caption
Trucks, water tanks and fracking equipment amassed on a gas pad near the town of Silt and the Grand Hogback Mountain Range. David Gilkey/NPR hide caption
Plastic surgeon Amy Pare says it's important for doctors to know what kind of substances patients she's treating might have been exposed to. Susan Philips/WHYY hide caption
William Reigle has fibrosis, a disease that may be aggravated by nearby fracking. He's one of more than 2 million Pennsylvanians who get their health care from Geisinger Health System. The system wants to use its extensive database of patient records to study the health impact of natural gas production. Maggie Starbard/NPR hide caption
Demand for natural gas has created a hydraulic fracturing or fracking boom; since 2008 over 5,000 new wells have been drilled nationwide. Workers at Chesapeake Energy, one of the biggest gas companies conducting fracking, are seen on the job site near Towanda, PA. David Gilkey/NPR hide caption
A working gas well head is fenced in just opposite of a home in Dish, Texas. Dish is about 30 miles north of Fort Worth. David Gilkey/NPR hide caption
A natural gas drilling rig's lights shimmer in the evening light near Silt, Colo. David Gilkey/NPR hide caption
Workers move a section of well casing into place at a natural gas drilling rig near Burlington, Pa. The industry is expected to drill as many as 10,000 new wells in the next few years. Ralph Wilson/AP hide caption