The amount of methane in many private water wells in North Texas has increased since 2011 but this rise cannot be linked to oil and gas drilling operations in the state, a new report released by the state Railroad Commission has claimed.

The latest report from the regulator reveals that measurements taken in September 2013 showed that the level of the explosive gas contaminating water had gone up in comparison to levels in 2010 and 2011, the Associated Press reported. However, despite claims from environmental groups and campaigners, the report concluded that there was insufficient evidence that the contamination was caused by or linked with drilling operations in the Barnett Shale.

According to Peter Pope, a geologist with the Railroad Commission, who prepared the report, the matter will not be investigated further. He suggested that residents of Weatherford, a suburb about 30 miles west of Fort Worth, where most of the wells are contaminated, should "ventilate and aerate" their water supply systems.

But previous studies on the link between water contamination and drilling operations have reached a different outcome. An independent scientific analysis of the methane in the neighborhood's water wells identified it as originating from a well operated by gas company Range Resources. A study by the U.S. Environmental Protection Agency in 2010 found that the methane was linked to Range's wells and the agency ordered the company to implement measures for cleaning up the water provided to residents of Weatherford.