Sinopec has halted drilling four wells in a gasfield near the city of Yulin in Shaanxi province, following a government investigation into water contamination in a village nearby, the company said via its official Weibo account on Sunday night.

The Yulin Environmental Protection Bureau said on June 21 that iron and manganese content exceeded the maximum level allowed for residential consumption in the village of Zhanggaotu near Yulin.

As a result, the city launched an investigation into emissions and waste dumping at three coal mines and Sinopec’s North China oil and gas subsidiary, the bureau said.

The bureau said the time that it planned to investigate how Sinopec disposed of liquid waste, mud and rock powders produced during the drilling process.

Sinopec’s gasfield on the border of Shaanxi province and Inner Mongolia has produced 3.3 billion cubic meters of natural gas since it started in 2005, Sinopec said.