She works at a health clinic in Burgettstown, Pa. — in the southwestern corner of the Keystone State where the rolling hills are now pockmarked with fracking wells in a natural-gas gold rush. In one sense, Allen and her co-workers at the Cornerstone Care community clinic are like a lot of health care professionals across the suddenly overwhelmed Marcellus Shale region of Appalachia: They’ve seen an increase in visit from anxious neighbors who are worried that symptoms such as increased headaches, dizziness, rashes, difficulty breathing, and various and sundry aches and pains might have something to do with these new wells, polluting the air that they breathe or the water that they drink.