When people think of industrial pollution, they generally think of chemical pollution. Chemicals can pollute air, water and soil. In some cases, entire communities are affected, such as in Love Canal, New York. The community of Love Canal was built on land that was once a chemical waste dump. The company that built the dump, the Hooker Chemical Company, capped the waste with what it thought was an impenetrable clay barrier. An explosion breached the barrier, allowing the waste to leach into ground water. The chemicals, called dioxins, were causing a large number of birth defects and miscarriages. The entire community had to be abandoned. In other cases, such as Leadville, Colorado, lead mining and tailings created very high concentrations of lead in the soil. The top layer of residential areas is currently being removed and replaced with uncontaminated soil. Lead can cause learning difficulties and cognition problems in children.