A Maryland report on hydraulic fracturing, or fracking, said the oil-drilling process could affect public health but likely would not cause earthquakes in the state. This Aug. 21, 2013, file photo shows an oil well near Tioga, N.D. (Karen Bleier/AFP/Getty Images)

Maryland’s latest report on the impact of proposed natural gas exploration in the western part of the state said drilling could pose a threat to air quality and workers in a region that is ecologically pristine.

But the report, presented to a state commission Monday, said the process called hydraulic fracturing would pose little threat of earthquakes, which were triggered recently in central Oklahoma by gas-drilling operations, according to researchers, and are of concern to environmentalists.

The report is the second of three called for under Gov. Martin O’Malley’s 2011 executive order to study hydraulic fracturing, an unconventional horizontal drilling process also referred to as fracking.

O’Malley (D) said studies of drilling impacts were required before a natural gas well could be built in Maryland. A third and final study funded by the Natural Resources and Environment departments is expected soon.

Several oil and gas companies have sought drilling permits and leased private land in hopes of exploring natural gas opportunities in remote Garrett County, home to the popular Deep Creek Lake. Their aim is to build wells in the Marcellus Shale, a 95,000-square-mile rock formation that stretches from Ohio to Virginia, where gas has been entombed for about 380 million years.

Hydraulic fracturing wells are typically drilled vertically for up to 5,000 feet, then horizontally for about a mile, according to experts. Up to 5 million gallons of water mixed with undisclosed amounts of chemicals are fired into the well to crack rock and release gas.

The American Petroleum Institute has called hydraulic drilling “a tried-and-true technology that promises thousands of new jobs and vast and indispensable supplies of clean-burning energy.”

But environmentalists say the process poses a severe threat to the environment, because of air pollution and other impacts. Meanwhile, President Obama, whom environmentalists have supported, has called natural gas use a key to the nation’s energy future.

The University of Maryland report presented Monday relied on numerous studies of drilling sites to warn that air pollution associated with gas exploration increased the risk of “adverse birth outcomes including congenital heart defects . . . sinus problems, eye burning, severe headaches, persistent cough and skin rashes.”

The report also found that traffic fatalities accounted for nearly half of underground gas exploration fatalities.

It recommends strict police and state agency monitoring of fracking operations if they are allowed in Maryland.