it appears even the heavily industrialized Ohio Valley has contributed to the ecological problem of lakes as far north as northern Ontario. Research from data gleaned up to the late 1980s demonstrated acid rain to have affected the biology of some 7,000 lakes. Prior to Vale's purchase of Inco, a major construction effort by Inco in the early 1990s dramatically scrubbed waste gases before pumping them up the Superstack. These upgrades were completed in 1994 and emissions from then on have been much reduced. By comparison to the plume prior to installation, the plume now disperses quite rapidly and is often see-through even at the stack site. Emissions reductions and increases in thermal efficiency have reached the point where natural draught is no longer sufficient to draw flue gas up the stack, necessitating the use of induced draught fans and/or reheating of the flue gas using natural gas burners. In contrast to the reduction of SO2 emissions, Inco's Superstack stands out in North America in its arsenic, nickel and lead emissions to the atmosphere. Using data compiled by the Commission for Environmental Cooperation, Inco alone accounts for 20% of all of the arsenic emitted in North America, 13% of the lead and 30% of the nickel. Although it is not strictly fair to compare a nickel-copper smelter to a lead smelter, by so doing one can get an idea of how poor the containment of lead is at Copper Cliff. In 1998, Inco emitted 146.7 tonnes of lead at Copper Cliff with a smelter production of 238,500 tonnes of nickel-copper matte. The EPA regulations in the United States require a primary lead smelter to limit emissions of lead to 3.0 gm per tonne of product. With this emission factor, Copper Cliff would be required to limit emissions of lead to approximately 1 tonne per year, demonstrating that the actual emission is about 150 times greater than allowed by US regulations for a lead smelter. Even with the 85% reduction postulated by Hatch, Inco would still emit 10 tonnes per year of lead, or four times the amount allowed by the EPA for a lead smelter. As a result of the excessive lead emissions from the Inco Superstack, the surrounding community of Copper Cliff was found to have levels of lead in soil tests at a level sufficient to cause harm to young children. See also List of chimneys List of