LOS ANGELES (AP) — The thirsty metropolis of Los Angeles plans to slash its use of imported water and instead spend up to $800 million to create drinking water pulled from one of the nation's largest Superfund pollution sites.

The Department of Water and Power will build the world's largest groundwater treatment centers over the San Fernando Basin, the Los Angeles Times (http://lat.ms/134bWpq ) reported.

Over the years, pollution from toxic chemicals such as perchlorate and trichloroethylene has made about half of the 115 groundwater wells in San Fernando Valley unusable. The pollutants were in solvents from industrial plants, military bases, car repair shops and even historic dairy operations.

The DWP began closing polluted wells in the 1980s but as the contamination plumes spread, the remaining wells could become unusable within seven years, according to the agency.

The DWP has relied on imported water to make up for the local supplies, but environmental restrictions have reduced Sierra Nevada imports and the cost of water from Northern California has risen 84 percent over the past decade.

Two treatment plants in North Hollywood could reopen the local wells and prevent others from closing, authorities said. One of the plants will process three times as much water per second as the world's current largest such facility, officials said.

Construction will begin in five years and the DWP hopes to have them open by 2022, producing about a quarter of the 215 billion gallons of water the city consumes each year, said Marty Adams, the DWP's director of water operations.

"By 2035, we plan to reduce our purchases of imported water by half," said James McDaniel, the DWP's senior assistant general manager.

The plant construction will mean a rate increase for DWP consumers, although some will be offset by reduced demand for imported water and by payments from polluters required under federal Superfund compensation laws.

Environmental groups applauded the treatment plans.

"The key thing is that Los Angeles is looking ahead. With climate change, we can no longer rely on snow in the Sierra Nevada range to be our reservoir," said Lenny Siegel, spokesman for the Center for Public Environmental Oversight.