Drilling down on shale gas.

Winter, Mary

Natural gas production hit a record high in 2012, with drillers delivering nearly 30 million cubic feet, an increase of 25 percent since 2006. Legislatures have been working at a similar pace, discussing how much to regulate the technology that's fueling the boom hydraulic fracturing.

In 2013, lawmakers in 31 states have introduced more than 170 bills related to hydraulic fracturing, a process in which drillers inject a mixture of highly pressurized water, sand and chemicals into underground shale, creating fractures that release trapped natural gas. Along with other technological advances, many experts believe hydraulic fracturing could make America energy independent by 2020 and supply the country with relatively cheap, clean energy for the next 90 years.

The natural gas boom has produced a recession-fighting financial windfall for local and state governments in Colorado, Louisiana, North Dakota, Oklahoma, Texas, Wyoming, among others, in the form of jobs, sales and severance tax revenue, lower gas prices and increased industrial activity.

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But the fast-growing practice of hydraulic fracturing also has seen stiff opposition. Homeowners in some suburban communities are concerned about the 24-hour activity, noise, odors and infrastructure damage drilling operations can cause, as well as their water consumption. Some environmentalists say hydraulic fracturing pollutes water and air with hazardous chemicals, endangering public health. They cite a 2011 Environmental Protection Agency study of water in heavily drilled Pavillion, Wyo., where residents complained of brown, foul-smelling water. The EPA said the groundwater contained compounds "likely associated with gas production practices, including hydraulic fracturing," and urged further study. Some have disputed the study, however and the scientific peer review of the draft report has been delayed.

Gas industry officials and others, including a number of government leaders, claim fears about hydraulic fracturing are overblown, and that charges against hydraulic fracturing are often untrue. They cite a February 2012 report by the University of Texas at Austin that found many water contamination problems blamed on the deep-underground injection of hydraulic fracturing fluids in fact had other causes, such as "well casing failures or poor cement jobs." Generally, contamination "can be traced to above ground spills or other mishandling of wastewater produced from shale gas drilling rather than from hydraulic fracturing," according to a UT Austin news release.

Lawmakers are busy sorting through the evidence. In New York and Vermont, they've passed temporary bans on hydraulic fracturing as they study its impacts on health and the environment. Similar legislation is under consideration in at least eight states, including California, where three bills introduced in 2013 carry bans of up to five years. If enacted, they would have a chilling effect on investment in the state, a gas industry spokesman has warned.

Another topic on lawmakers' agenda is whether to require drilling companies to disclose the names and concentrations of chemicals used in hydraulic fracturing fluids. At least 14 states now require such disclosure, although several allow companies to withhold the names of chemicals they want to keep secret from competitors, and that's a problem, say critics. A Bloomberg analysis last year showed that U.S. companies claimed trade-secret exemptions on 22 percent of the chemicals they used. Texas Representative Lon Burnam (D), a co-author of that state's disclosure bill, says he had to make concessions to win passage, and the resulting law falls short of keeping the public fully informed of the chemicals drillers bring into their communities.

Additionally, in 2013:

* Lawmakers in at least 22 states introduced bills addressing severance taxes on drilling operations; as of May, seven states enacted legislation. The bills vary significantly. Some states look to impose taxes or amend existing ones, while others seek to alter revenue allocation methods or introduce tax exemptions and credits for certain wells.

* In at least 16 states, lawmakers proposed regulations involving well construction, spacing between wells, water withdrawal, wastewater handling and other measures to protect water resources.

* In at least five states, legislatures considered proposals addressing who should govern hydraulic fracturing, with most assigning authority to the states.