The Environmental Protection Agency has told Oklahoma regulators to do more to protect the state from a surge in earthquake activity that scientists have linked to the underground disposal of oil and gas wastewater.

An EPA administrator sent a letter in November to the Oklahoma Corporation Commission, saying a magnitude 5.0 earthquake happened despite state and federal action to curb wastewater injection. The Frontier first reported the contents of the letter.

Well-related pressure buildup can affect health and underwater drinking water sources, said the letter, dated Nov. 22.

The commission's response to the EPA, dated Nov. 29, said Oklahoma will continue to work with federal officials and made note of a governor's task force on wastewater. That group's study is expected later this month.

Year-end data from the Corporation Commission show disposal well operators placed about 23 percent less wastewater into the earthquake zone in 2016 compared to the previous year.

Oklahoma Attorney General Scott Pruitt is President Donald Trump's pick to head the EPA. His nomination is pending Senate approval.

Environmentalists have criticized Pruitt for not doing more to reduce seismic activity linked to oil and gas production in Oklahoma.

The EPA sent the letter to Oklahoma while President Barack Obama was in power. The Trump administration could take a different stance on scaling back on oil and gas wastewater disposal.

Explore further Oklahoma warns of more quakes from energy drilling

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