"Emergency pollution control crews worked to clean a potentially serious oil spill from the River Des Peres as attempts were made to patch its sources at the Great Lakes Carbon Corp. coke plant on the South Side Thursday. The oil has been leaking into the river from a lagoon that contains an estimated 3 million gallons of waste products, authorities said. Carl Walter, chairman of an environmental response team investigating the incident, estimated that several hundred gallons of oil have leaked through the eastern side of the lagoon since at least Monday. 'But while it is small in quantity, it could pose potentially serious problems,' he said."