[...] Just over a generation ago, refuse was rarely a problem because families, then largely poor and rural, used and reused everything. As cities have grown, urban support systems have been unable to keep up with the growing demand for the processing and disposing of waste. Most landfills are poorly managed and have only thin linings of plastic or fibreglass. These sites leach heavy metals, ammonia and bacteria into the groundwater and soil, and the decomposing waste sends out methane and carbon dioxide.