There are thousands of dirty old drill sites in Colorado. The state gave oil firms a $1bn pass

Investigation reveals regulator let firms off the hook on cleanup bonds despite backlog that will take decades to clear

When Christiaan van Woudenberg moved to Erie, Colorado, in 2007, he never imagined he would become an anti-fracking activist. He simply thought he was buying his dream home – a four-bedroom with a panoramic mountain view, 30 minutes north of downtown Denver.

Then, in 2014, the drilling started. Oil and gas rigs sprang up, some just 800ft (240m) from his bedroom window. The dream turned to nightmare: loud noises rumbled all night long, and the air stank like exhaust. Neighbors started getting headaches and nosebleeds, and Van Woudenberg developed new respiratory issues. He kept his windows shut and worried about his daughters going outside.