A vast pool of natural gas lies trapped in shale nearly a mile below the surface under most of Western Pennsylvania. Marcellus Shale gas development has pitted the interests of industry and economic gains against environmental concerns. The high-profile issue is hydrofracturing, which is the controversial technique that breaks open tight shale layers with a mixture of water, chemicals and sand pumped at very high pressure.

Fracking and concerns over chemical contamination of water wells or surface water represent the first wave of Marcellus Shale development.

The second wave, which has a lower profile than fracking, is coming — with pipelines.

Though not as controversial as fracking, pipelines do raise concerns among many people.

President Barack Obama postponed a decision until after next year’s elections on a proposed pipeline extending from the Alberta tar sands in Canada to Gulf Coast refineries in Texas because it was so controversial. The pipeline project pits environmentalists against union workers, two key Obama constituencies. So he punted.

But pipelines are necessary to transport natural gas from rural areas where it comes out of the ground to markets, generally larger, metropolitan areas.

Natural-gas pipelines have for decades spanned the country and the state. These underground pipelines are rarely given much thought. But that can change — and did — when a massive and deadly September 2010 explosion in San Bruno, near San Francisco, raised awareness of the potential for disaster with poorly constructed or rarely inspected natural-gas pipelines.

After Marcellus Shale gas is extracted, it has to be moved to markets. And to move the gas from wells in rural areas, new pipelines called gathering pipelines must be constructed to bring the gas to the existing network of transmission lines.

The problem in Pennsylvania comes as pipeline construction seems to be proceeding faster than regulation or inspection capabilities can keep up. There also are loopholes or gaps in regulations, such as a set of regulations for gas pipelines in highly populated areas, but next to nothing covering pipelines in rural areas — just the sort of places where Marcellus wells are being drilled.

The Philadelphia Inquirer just published a lengthy story on the issue featuring the headline, “Powerful pipes, weak oversight.”

The reporters found minimal regulation over pipelines in rural areas and also discovered that federal and state regulators often don’t even know where the pipelines are being installed. Because of a lack of coordination and confusion over jurisdiction, the Inquirer noted that high-pressure pipelines are being constructed with “no government safety checks — no construction standards, no inspections and no monitoring.”

Older pipelines, like the one that exploded in San Bruno and those that caused explosions in Allentown and Philadelphia, are constructed of cast iron. Pipelines today are being made of steel and are believed to be much safer. Still, pipe sections have to be welded together, and the pipeline companies contract out construction work, including weld inspection.

Another concern is that the demand for gathering pipelines is growing so rapidly that companies are finding it difficult to hire qualified workers.

While less controversial than fracking and gas drilling, the transmission line issue does add to the responsibilities that state and federal lawmakers have to make Marcellus Shale gas development as safe as possible, while not putting unwarranted burdens on the industry’s ability to develop and to create jobs and economic growth here.

Pipeline companies say they are doing quality work on the pipelines being constructed now. And that’s probably true — the companies know that leaks or explosions can be costly, in terms of both money and public relations.

But still, there must be standards, clear regulations and lines of authority explaining which governmental agencies, state or federal, will monitor the work, do pipeline inspections and handle ongoing oversight. The current confusion between the role of the state Public Utility Commission and the federal Pipeline and Hazardous Materials Safety Administration (PHMSA) must be clarified — and quickly.

Transmission pipelines are essential, and no doubt safer than ever. But with an estimated 10,000 to 20,000 miles of new natural-gas pipelines expected to be coming to Pennsylvania, more attention needs to be paid to pipeline construction and monitoring.