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

itoggle caption David Gilkey/NPR

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

itoggle caption Susan Philips/WHYY

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

itoggle caption Maggie Starbard/NPR

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

itoggle caption David Gilkey/NPR

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

itoggle caption David Gilkey/NPR

A natural gas drilling rig's lights shimmer in the evening light near Silt, Colo. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

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

itoggle caption Ralph Wilson/AP