Guardian: One day in November, mysterious black piles appeared on the banks of the Detroit River, not far from the Motor City's downtown and right next to the Ambassador Bridge, the busiest international crossing in North America. These huge stockpiles of petroleum coke, the byproduct of refining tar sands oil at the Marathon refinery in south-west Detroit, are owned by Koch Carbon, run by businessmen Charles and David Koch. This series of photographs takes a closer look at the people the petroleum coke piles...