The U.S. Environmental Protection Agency has given California regulators a series of deadlines -- some coming as soon as next week -- for developing plans of action and producing other information related to the state's oversight of oil field waste injection wells.

Contained in a letter the federal EPA sent state officials July 17, the deadlines make clear that federal pressure is driving the state's recent focus on disposal wells, including its emergency shutdown last month of 12 Kern County injection wells, two of which have since been allowed to reopen.

The EPA's concern is that the state may have granted permits for wells that inject produced water into aquifers that either contain federally protected drinking water or are located near existing water wells.

The letter opens with a statement that the Safe Drinking Water Act, passed by Congress in 1974, authorizes the EPA to protect underground sources of water.

"This role is of particular importance at this time of drought and diminished water supplies," Jared Blumenfeld, EPA Regional Administrator for the Pacific Southwest, wrote in the letter to John Laird, secretary of the California Natural Resources Agency, and Matt Rodriquez, secretary for environmental protection at the California Environmental Protection Agency.

The letter traces the EPA's ongoing scrutiny of California injection wells to a 2011 audit faulting DOGGR's oversight of the injection well program. The federal government had given the state primary authority for regulating such facilities in 1983.

In 2012, a separate federal review raised questions about whether California injection wells had been allowed to operate outside the boundaries of aquifer exemptions granted by the EPA.

That review was followed by DOGGR's broad review of its UIC program. Last month's emergency well shutdowns were a result of that review.

By the letter's first deadline of Aug. 16, DOGGR is expected to turn over a list of every injection well in the state that has been permitted to inject into non-oil-producing formations containing what is generally considered to be federally protected drinking water.

On the same date, DOGGR is to provide a status report on its 2012 action plan for addressing "deficiencies" in California's regulation of what are known as Class II Underground Injection Control wells. Most such wells involve oil production, but the ones the federal government has recently focused on dispose of produced water, a saline byproduct of oil production.

Also by Aug. 16, the federal EPA wants "all documents" pertaining to California's requests for aquifers to be exempted from the federal Safe Drinking Water Act, as well as the EPA's responses to those requests and any related state appeals.

Within 60 days of the date of the letter, or Sept. 15, DOGGR is expected to give the EPA its "initial assessment of whether any existing and potential sources of drinking water are at risk of contamination from improper Class II injection."

As part of that deadline, the EPA wants the location of private and public water wells that "may be at risk" from injection wells. It also asked for a plan to "ensure protection of human health" from injection wells, as well as a plan to share such information with the public, in coordination with other state agencies including the State Water Resources Control Board and the Department of Public Health.

Also within 60 days of the letter's date, DOGGR is expected to produce a plan and timetable for creating a searchable database of all the state's Class II wells. That system must include a map overlay showing the wells' locations, geological formations and federal aquifer exemptions.

By Oct. 15, DOGGR is to provide a list of all California Class II wells permitted to inject in oil-producing aquifers containing water not generally considered to be federally protected drinking water.