The new pollution limits are contained in a proposed "General Permit 5," now under final consideration by the state Department of Environmental Protection, and would significantly reduce emissions of nitrogen oxides or "NOx" -- a primary component of unhealthy ozone, smog and acid rain. They also would apply to other pollutants from well drilling, compressor station and pipeline pumping engines of less than 1,500 horsepower that emit less than 100 tons of the pollutant annually.

But after two years of lobbying by the gas drilling industry, the DEP decided to allow the engines to emit three times more air pollution than what was initially proposed by the DEP's Bureau of Air Quality in 2010, even though emissions-controls manufacturers say their equipment can meet lower emissions limits.

The higher pollution limits allowed in the proposed general permit could cause significant air quality deterioration in coming years as Marcellus Shale wells, pipelines and compressor stations multiply, according to a 55-page comment document by the Clean Air Council, a Philadelphia-based environmental organization, and seven other environmental and community groups.

"We'd like to see policy based on relevant science. That's what should be at the heart of this thing," said David Presley, a Clean Air Council attorney. He said the DEP increased the emissions limits in the general permit proposal based solely on drilling industry objections and didn't verify the accuracy of claims that the technology isn't applicable.

The U.S. Environmental Protection Agency also was critical of general permit control requirements for larger engines known as "synthetic minor sources" -- those that would have emissions of more than 100 tons of NOx a year if not for the use of controls. And the agency urged the DEP to consider the cumulative impact that issuing numerous general permits could have on air quality standards.

The DEP can institute a general permit program for such "minor sources" if it determines that air pollution sources in a particular category are similar and standardized regulations can be applied. Such a "one-size-fits-all" regulation is favored by industry because it streamlines the permitting process to less than 30 days. The proposal under review also would eliminate the opportunity for public comment on individual gas development operations.

DEP spokesman Kevin Sunday said in written responses to questions about the proposed permit that the DEP is making sure the GP-5 will protect the environment by requiring natural gas developers to use "best available control technology."

"For the most common lean burn engine (1340/1380 horsepower), the new limits will represent a 75 percent reduction in allowable NOx. For the rich burn engine, a 90 percent reduction," he wrote. "Simply put, the proposed GP-5 means cleaner air as gas development unfolds."

The proposed general permit also doesn't require gas-development operations to use updated engine emissions control technology as it becomes available and economically viable. Such provisions should be, and usually are, included in the text language of other general permits, according to the Clean Air Council comments.

"The proposed general permit is not pushing the envelope. It's not going further than the individual permits the DEP is issuing now," Mr. Presley said. "Best available technology standards are supposed to push the envelope and set emission controls that companies have to attain."

While it's true the proposed general permit reduces nitrogen oxides emissions limits from 2.0 to 0.5 grams per horsepower hour, Mr. Presley said, that lower rate is already regularly achieved by many natural gas-powered engines. He said a NOx emissions limit of 0.15 grams -- three times lower than the 0.5 gram limit in use -- is achievable using Selective Catalytic Reduction, or SCR, controls.

The higher 0.5 gram emissions limits were sought in the proposed GP-5 by the Marcellus Shale Coalition, an industry lobbying organization, and individual drilling companies in several industry-only meetings and a series of email exchanges with the DEP over the past two years as well as public comments submitted during the spring of 2012.

According to the coalition's nine-page comment document, it doesn't dispute that SRC technology would reduce emissions but contends that such equipment is complex, unreliable and too expensive.

"Some of those engines using natural gas fuel already have much lower emissions, and we don't want to unnecessarily retard or reduce the viability of the industry," said Kathryn Klaber, the Marcellus Shale Coalition president and executive director. "That could happen if the technology is so stringent so as to damage the economical collection of natural gas and the industry's competitive balance."

Joe Aleixo, an engineer with DCL International Inc. in Toronto, a supplier of pollution controls worldwide, said SCR is the "state of the art'' technology for reducing NOx emissions in diesel and lean-burn natural gas-fired engines, turbines, power generators and trucks.

"It's widely used and well proven for over 30 years, and its ability to handle changing load conditions has improved significantly in the last decade," Mr. Aleixo said. "It's been used in some gas compressor applications, but its use has been limited because the industry has been successful in lobbying to use other control technology."

According to Mr. Aleixo, adding SCR controls to engines isn't cheap and can cost $200,000 to $300,000 for some of the bigger engines. But it is competitive with engine-modification equipment, he said, which can vary widely in cost, from $50,000 to $500,000. Such engine combustion modifications are favored by the gas drilling and collection industries.

SCR controls have been used on gas-drilling engines in Wyoming, where NOx emissions have been reduced 90 to 98 percent, said Wilson Chu, business development manager for emissions-controls supplier Johnson Matthey, which has an office in Audubon, near Philadelphia. He said SCR costs for smaller 1,300-horsepower engines, those covered by the proposed general permit, have come down by 30 to 40 percent in recent years.

He said Johnson Matthey has sold some SCR controls to Marcellus Shale companies trying to keep the emissions of bigger and aggregated drilling and collection operations below the "major source" emissions level of 100 tons of NOx a year, where additional controls and permitting requirements would apply.

"Right now their use in gas-drilling operations is not widespread, and if you aren't aggregating their emissions, those operations are not above the [100-tons-a-year] threshold," Mr. Chu said. "But if all of those operations are spewing out 40 tons of NOx a year, that's still a lot of NOx."

The DEP published the latest version of the proposed general permit in the March 3, 2012, Pennsylvania Bulletin and requested public comments. The comment period ended in May. The DEP hasn't issued its required "comment and response document" yet, although a draft of that document and final permit language has been under review by DEP Secretary Michael Krancer and executive level staffers since Nov. 1.

Mr. Sunday said the final general permit language will be released soon.

Don Hopey:  This email address is being protected from spambots. You need JavaScript enabled to view it.  or 412-263-1983.