Western Pennsylvania is considered the birthplace of commercial oil drilling. On Aug. 27, 1859, Edwin Drake struck oil in Titusville, Pa., and changed the course of history. Now, people there are busy trying to stop wells and the increasingly pervasive drilling practice known as fracking. Fracking is the popular term for hydraulic fracturing, the technique used to extract natural gas from deep beneath the earth’s surface. Fracking is promoted by the gas industry as the key to escaping from dependence on foreign oil. But evidence is mounting that fracking pollutes groundwater with a witches’ brew of toxic chemicals, creating imminent …