Chesapeake Energy Corp. said Thursday crews have significantly reduced the flow of the chemical-laden water from its out-of-control well near Canton in Bradford County.
Spokesman Brian Grove says the cause of Tuesday night's breach is unknown but it's located in a wellhead connection.
Thousands of gallons of drilling fluids spilled. They escaped containment, crossed farm fields and entered a stream.
Grove says initial testing of area waterways has shown "minimal impact, if any."
The gas drilling technique is called hydraulic fracturing, or fracking. It involves blasting chemical-laced water into the ground. Critics say it could poison water supplies; the gas drilling industry says it's safe.