At a news conference Monday, the Sierra Club and Environment Texas said the U.S. Environmental Protection Agency and the Texas Commission on Environmental Quality have failed to hold Shell accountable, The Houston Chronicle reported. The groups said that the agencies have not enforced the Clean Air Act at Shell's refinery on the Houston Ship Channel.

"On average, more than once a week, Shell Oil Co. has self-reported that it violated its permit limits and released millions of pounds of chemicals and harmful pollutants into the air around the Houston Ship Channel," said Luke Metzger, head of Environment Texas. "Already, Shell Oil is authorized to emit staggering amounts of pollutants into the air, and with Houston's air as bad as it is, it is simply unforgivable for them to exceed those permits."