In 2019, oil was found seeping from a California railyard into the Sacramento River; six years later, cleanup had removed 75,000 gallons of oil and 100,000 tons of contaminated soil.

We measure pollution by what we can see: smoke rising from factories, plastic floating in rivers, or oil spreading across the surface of water. But some of the most persistent environmental damage happens quietly, beneath the ground, sometimes for generations.

Among those hidden places, A railway yard may seem like an unlikely place for an environmental crisis, but what lies beneath the ground can sometimes be more dangerous than what meets the eye. And that's exactly what happened in California, US.In Dunsmuir, California, oil from an old locomotive-fuelling facility had been leaking into the surrounding soil and the Sacramento River for decades.

It was not until in 2019, that the scale of the contamination came forward only when authorities began investigating the seepage.The investigation revealed that the problem was much older than initially understood. According to the US Environmental Protection Agency (EPA), the contamination could be traced back to the early 1900s, when leaking tanks and equipment were used to fuel locomotives at the railyard.