WASHINGTON, June 21 (Reuters) - The U.S. Environmental Protection Agency will review Texas' oversight of wells used for injecting oil drilling wastewater and carbon dioxide into the ground after "substantial concerns" from environmental groups that the operations are behind a spate of well blowouts, sinkholes and seismic activity.

The EPA announced the review in a May 23 letter to the environmental groups that was seen by Reuters on Friday.

A spokesperson for the EPA did not immediately respond to a request for comment.

Nine Texas-based environmental and watchdog groups led by Commission Shift and Clean Water Action requested the review in March.

Texas has authority to permit so-called "class II" injection wells, which are used to dispose of drilling wastewater, as well as for injecting carbon dioxide underground to enhance oil recovery in active fields.

Parts of Texas, especially the Permian oil basin in the west of the state, have been beset by frequent incidents of blowouts of unplugged wells and seismic activity linked to the injection of wastewater into the subsurface, the petitioners said.

The groups had urged the U.S. regulator to evaluate whether the Texas Railroad Commission, the state agency that regulates oil production, exploration and transportation, is meeting federal standards under the Safe Drinking Water Act to safeguard public health and the environment.

A spokesperson for the Railroad Commission said on Friday that it has not yet been contacted by the EPA and stood by its track record.

"The RRC has a long-standing history of regulating underground injection that is protective of the environment and public safety," commission spokesperson Patty Ramon said in an e-mail.

There are approximately 180,000 Class II injection wells across the United States, with the largest concentration in Texas, according to the EPA.

The groups that filed the petition raised concerns that there is no recourse from the RRC when they get reports of poorly managed class II wells and that the regulator has not examined the root causes of well leaks and blowouts or open well permitting decisions to the public.

"We believe that a rigorous and transparent evaluation by the EPA will ultimately lead to stronger protections for our water resources and greater accountability for regulatory practices," said Virginia Palacios, executive director of Commission Shift.

The RRC has also applied for authority, or "primacy," from the EPA to run its own permitting program for injecting carbon dioxide underground for permanent storage.

Commission Shift said the concerns raised around its management of wastewater disposal and carbon for oil recovery raise red flags around its ability to regulate carbon sequestration.

(Reporting by Valerie Volcovici; Editing by Rod Nickel and Aurora Ellis)