A fracking structure (left) next to a more conventional drilling operation Reuters

Scientists have found dangerous levels of toxic chemicals in ground water from a fracking operation in a small Wyoming town.

In one example, levels of benzine, a flammable liquid used in fuel, were 50 times above the allowable limit in the water used by the 230 residents of the town of Pavillion in central Wyoming, according to research published in the Journal of Environmental Science and Technology.

The discovery was made three years after the federal Environmental Protection Agency pulled the plug on a investigation into possible contamination of the water by the fracking operation after residents complained of the smell and taste of their water.

Scientist Dominic DiGiulio and Stanford University Professor Robert Jackson discovered that workers were drilling at very shallow depths, placing the fracking operation uncomfortably close to the drinking water aquifer that supplies the wells used by Pavillion residents. They also found that chemicals were being dumped into unlined pits allowing them to leach into the ground.

"What happened there could happen elsewhere," DiGiulio told The Guardian. It was concerning how shallow the drilling was. There's not much of a buffer to where people draw their water."

Fracking — which involves injecting water and chemicals into the ground to force pockets of gas and oil from rock — is highly controversial in the US, but lightly regulated. Fracking has been linked not only to contaminated water but to earthquakes as well.

Jackson believes the EPA ended its study because of "cold feet" at a time when the Obama administration was promoting the expansion of natural gas as a way to lower the US's greenhouse gas emissions.

"It was a time of great contention as natural gas was a fossil fuel pillar for the administration," he said. "It's important to say that fracking is often done safely. But in the instances where something goes wrong, we need to know and we need to learn from them."