United States through a man-made conveyance such as a road, ditch or pipe. Alternatively, a small CAFO may be designated an ordinary animal feeding operation (AFO) once its animal waste management system is certified at the site. Since it first coined the term, the EPA has changed the definition (and applicable regulations) for CAFOs on several occasions. Private groups and individuals use the term CAFO colloquially to mean many types of both regulated and unregulated facilities, both inside and outside the U.S. The definition used in everyday speech may thus vary considerably from the statutory definition in the CWA. CAFOs are commonly characterized as having large numbers of animals crowded into a confined space, a situation that results in the concentration of manure in a small area. Key issues Environmental impact The EPA has focused on regulating CAFOs because they generate millions of tons of manure every year. When improperly managed, the manure can pose substantial risks to the environment and public health. In order to manage their waste, CAFO operators have developed agricultural wastewater treatment plans. The most common type of facility used in these plans, the anaerobic lagoon, has significantly contributed to environmental and health problems attributed to the CAFO. Water quality The large amounts of animal waste from CAFOs present a risk to water quality and aquatic ecosystems. States with high concentrations of CAFOs experience on average 20 to 30 serious water quality problems per year as a result of manure management issues.Animal waste includes a number of potentially harmful pollutants. Pollutants associated with CAFO waste principally include: nitrogen and phosphorus, collectively known as nutrient pollution; organic matter; solids, including the manure itself and other elements mixed with it such as spilled feed, bedding and litter materials, hair, feathers and animal corpses; pathogens (disease-causing organisms such as bacteria and viruses); salts; trace elements such as arsenic; odorous/volatile compounds such as carbon dioxide, methane, hydrogen sulfide, and ammonia; antibiotics; pesticides and hormones. The two main contributors to water pollution caused by CAFOs are soluble nitrogen compounds and phosphorus. The eutrophication of water bodies from such waste is harmful to wildlife and water quality in aquatic system like streams, lakes, and oceans. Because groundwater and surface water are closely linked, water pollution from CAFOs can affect both sources if one or the other is contaminated. Surface water may be polluted by CAFO waste through the runoff of nutrients, organics,