PITTSBURGH (AP) — The final report from a landmark federal study on hydraulic fracturing, or fracking, found no evidence that chemicals or brine water from the gas drilling process moved upward to contaminate drinking water at a site in western Pennsylvania. Scientists used tracer fluids, seismic monitoring, and other tests to look for problems, and created the most detailed public report to date about how fracking affects adjacent rock structures. The fracking process uses millions of gallons of high-pressure water mixed with sand and chemicals to break apart rocks rich in oil and gas.