Four earthquakes have been confirmed in the Eagle Ford Shale of South Texas in the past two weeks. The strongest were 3.1 magnitude, according to the U.S. Geological Survey.
The latest measured 2.5 magnitude and struck on Saturday with an epicenter about five miles east of the Gonzales County town of Smiley. No damage was reported.
Five days earlier, a 3.1 magnitude quake struck in the area. Another 3.1 magnitude earthquake was recorded May 12 south of the town of Westhoff in DeWitt County.
On May 11, a 3.0 magnitude quake struck a few miles east of Gillett, a town in Karnes County.
There have been seven earthquakes recorded in the Eagle Ford Shale of South Texas this year.
Environmentalists blame the tremors on saltwater disposal wells, which inject wastewater generated in the hydraulic fracturing process and other oil and natural gas activities deep underground.
Saltwater disposal wells are regulated by the Railroad Commission of Texas, the state agency that regulates the oil and natural gas industry.
Railroad Commission officials adopted stricter regulations for saltwater disposal wells in November 2014. Over the last four years, the agency received 367 disposal well applications in areas of historic seismicity.
Of those proposed projects, 163 permits were issued with special conditions that include reducing maximum daily injection volumes and pressures as well as being required to record volumes and pressures on a daily basis as opposed to monthly.
Fifty-four disposal applications were returned or withdrawn. Eleven applications were sent to hearing. Twenty-one permits were issued without special conditions and 118 applications are pending technical review.