The Environmental Protection Agency is expanding the monitoring of ground water in the Whittier Narrows area of the San Gabriel Valley Area Superfund site.
Cost of the five-year plan was estimated at $5.2 million, including $900,000 for sampling existing wells and $4.3 million for installing and sampling new wells, federal EPA officials said.
The water is safe and does not need to be cleaned up, but expansion of monitoring was approved to ensure health and environmental protection, the EPA said.
The San Gabriel Valley Area Superfund site, which was added to the EPA's national priorities list in 1984, is being monitored because of ground water contamination by substances known as volatile organic compounds.
Whittier Narrows lies between the San Gabriel and Rio Hondo rivers near South El Monte.
The EPA said that as many as 17 new wells will be added to its existing monitoring network, beginning as early as this summer.
The EPA said an agency study conducted last September found that Whittier Narrows drinking water met federal and state standards and did not pose any health risks. It also found that chemical concentrations remain at low levels and had not increased over the last several years.
The agency said that if the expanded monitoring reveals increasing contamination, the EPA could begin efforts to extract the ground water and treat it.
The EPA and the Los Angeles Regional Water Quality Control Board are conducting investigations to find the sources of contamination in order to evaluate cleanup alternatives.
The Superfund is the government's toxic waste cleanup program. The national priorities list is the EPA's slate of hazardous-waste sites judged to pose the greatest long-term health and environmental threats.