A view shows the Walmart logo at a Walmart store in North Bergan, New Jersey in this Nov 22, 2012 file photo. [Photo/Agencies]

LOS ANGELES - The world's largest retailer, Walmart Stores, Inc. pleaded guilty Tuesday of violating the Clean Water Act and will pay more than $81 million to settle the case.

The US Attorney's Office announced that Walmart admitted in San Francisco six misdemeanor counts of negligently violating the Clean Water Act by illegally handling and disposing of hazardous materials at its retail stores across the United States.

The Bentonville, Arkansas-based company will pay approximately $81.6 million for its unlawful conduct, the office said.

"Retailers like Walmart that generate hazardous waste have a duty to legally and safely dispose of that hazardous waste, and dumping it down the sink was neither legal nor safe," Attorney Andre Birotte Jr. said.

Documents show that up until January 2006, Walmart did not have a program in place and failed to train its employees on proper hazardous waste management and disposal practices.

As a result, hazardous wastes were either discarded improperly at the store level -- including being put into municipal trash bins or, if a liquid, poured into the local sewer system -- or they were improperly transported without proper safety documentation to one of six product return centers in the country.

"By improperly handling hazardous waste, pesticides and other materials in violation of federal laws, Walmart put the public and the environment at risk and gained an unfair economic advantage over other companies," said Ignacia S. Moreno, assistant attorney general for the US Justice Department's Environment and Natural Resources Division.

The fines will go in part to fund environmental projects in the communities affected by the violations and help prevent future harm to the environment, Moreno added.

In addition to the civil penalties, Walmart is required to implement a comprehensive, nationwide environmental compliance agreement to manage hazardous wastes generated at its stores.

The agreement includes requirements to ensure adequate environmental personnel and training at all levels of the company, proper identification and management of hazardous wastes, and the development and implementation of Environmental Management Systems at its stores and return centers.

With more than 4,000 stores in the United States, Walmart sells thousands of products which are flammable, corrosive, reactive, toxic or otherwise hazardous under federal law.

The products that contain hazardous materials include pesticides, solvents, detergents, paints, aerosols and cleaners. Once discarded, these products are considered hazardous waste under federal law.