By Matthew Daily

Associated Press

WASHINGTON (AP) - Hydraulic fracturing to drill for oil and natural gas has not caused widespread harm to drinking water in the United States, the Environmental Protection Agency said Thursday in a report that also warned of potential contamination of water supplies if safeguards are not maintained.

A draft study issued by the agency found specific instances where poorly constructed drilling wells or improper wastewater management affected drinking water, but said the number of cases was small compared to the large number of wells that use hydraulic fracturing, better known as fracking.

The EPA assessment tracked water used throughout the fracking process, from acquiring the water to mixing chemicals at the well site and injecting so-called “fracking fluids” into wells, to collection of wastewater, wastewater treatment and disposal.

The report identified several vulnerabilities to drinking water resources, including fracking’s effect on drought-stricken areas; inadequately cased or cemented wells resulting in below-ground migration of gases and liquids; inadequately treated wastewater discharged into drinking water resources; and spills of hydraulic fluids and wastewater.

Congress ordered the long-awaited report in 2010, as a surge in fracking fueled a nationwide boom in production of oil and natural gas. Fracking rigs have sprouted up in recent years in states from California to Pennsylvania, as energy companies take advantage of improved technology to gain access to vast stores of oil and natural gas underneath much of the continental U.S.