California regulators are proposing a strict limit on a toxic man-made chemical that has contaminated water supplies throughout the state, particularly in its vast agricultural heartland.
California would be the second state, after Hawaii, to establish a threshold for the former pesticide ingredient and industrial solvent known as TCP (1,2,3-trichloropropane) in drinking water. The chemical compound, identified in California as a human carcinogen, is no longer in wide use but has leached over the years into many wells and reservoirs in California and other states.
The California State Water Resources Control Board’s proposal would set the maximum allowable amount of TCP in public tap water at five parts per trillion — the lowest level that existing filtration systems can reliably detect and far lower than Hawaii’s.
It “is a top priority for the state water board,” said board spokesman Andrew DiLuccia.
TCP taints water systems serving nearly a million people from Sacramento to San Diego, according to the state water board. The compound is present at levels above the proposed limit in 562 wells, reservoirs and other sources belonging to 94 public water systems, according to 2016 data. Those numbers do not include private wells.
Citing federal data, the Environmental Working Group, a Washington, D.C.-based advocacy organization, says the chemical also has been detected in water supplies of a dozen other states, including New York, Pennsylvania and New Jersey, as well as Puerto Rico. The group, or EWG, said the extent of contamination is likely underestimated because federal tests used a contamination threshold much higher than California’s. (The federal government does not set restrictions on TCP in drinking water.)
Once TCP gets into the groundwater, it “persists for centuries,” according to the EWG’s April report.
In California, the contamination exists in many urban areas, including in Los Angeles, San Bernardino and San Mateo counties. Though the source in those more populated regions is not known, the pollution is believed to come from industrial and hazardous waste sites.
“Los Angeles has quite a bit of contamination,” said Andria Ventura, toxics program manager for the environmental advocacy group Clean Water Action. “It’s hard for water providers to pinpoint where it came from.”
But California’s most serious and widespread TCP contamination is in the agricultural counties of the Central Valley, where the chemical was an ingredient in soil fumigants sold by the Shell Oil and Dow Chemical companies from at least the 1950s into the 1980s.
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