The <a href=http://www.eoearth.org/article/Groundwater title=Groundwater>groundwater</a> near the landfill is closely monitored for signs of contamination from the leachate.</p><p>As the buried wastes are decomposed by <a href=http://www.eoearth.org/article/Bacteria title=Bacteria>bacteria</a>, gases such as methane and carbon dioxide are produced.