HARRISBURG — Pennsylvania needs more inspectors and greater wastewater treatment capacity to better handle the strong interest in drilling on Marcellus shale, a mostly untapped reservoir of natural gas that holds huge potential, a top state environmental official said Tuesday.

John Hanger, the acting secretary of the state Department of Environmental Protection, told a state House panel that while his department is able to adequately protect the environment, he also has concerns.

For instance, his department will need dozens more people to process drilling permit applications in a timely fashion and inspect drilling sites to help ensure that the drilling operations are not contaminating waterways or groundwater, Hanger said.

In addition, the state's capacity to treat contaminated drilling water is running out as more exploration companies begin drilling, he and industry officials testified.

"We're just at the beginning of this rush and there will be even more activity in the very near future and we need to frankly gear up," Hanger said in an interview after the hearing.

To date, exploration companies have spent about $2 billion on leasing land, performing seismic studies and other activities in pursuit of Marcellus Shale gas, an industry official said. Companies as large as ExxonMobil Corp. have shown interest in Pennsylvania, which is one of four states that sit atop the 54,000 square-mile formation.

With the price of natural gas tripling in recent years, exploration companies are more willing to spend millions of dollars to drill into the shale, a process that can involve the high-pressure injection of a million or more gallons of chemically treated water to break up the shale and release the gas.

About 40 percent of the water used returns to the surface, said Tom Beauduy, the deputy director of the Susquehanna River Basin Commission.

Department of Environmental Protection officials said that, so far, they have detected no environmental contamination problems from the drilling, although they have received a couple complaints about well-water supplies being temporarily interrupted by the drilling.