Originally published in EcoWatch

For decades, Shell and Dow hid a highly potent cancer-causing chemical in two widely used pesticides, contaminating drinking water for millions of people in California and beyond, according to lawsuits detailed in a new report from the Environmental Working Group (EWG).

The chemical 1,2,3-trichloropropane or TCP, was formerly an unwanted and ineffective byproduct in Dow’s Telone and Shell’s D-D pesticides. Internal documents uncovered in lawsuits filed by communities in California’s San Joaquin Valley show that the companies saved millions of dollars a year by not properly disposing of TCP, a chemical a Dow scientist once called “garbage,” as hazardous waste.

Shell stopped making D-D in 1984 and Dow later took TCP out of Telone, but not before it contaminated the tap water supplies of 94 California utility districts serving 8 million people.

A U.S. Environmental Protection Agency testing program found TCP in tap water supplies for about 4 million people in 13 other states between 2013 and 2015, but the chemical is unregulated at the federal level and in every state except Hawaii.

Regulators in California will meet next week to decide whether to set a legal limit for TCP in tap water. Shell and Dow have paid multi-million dollar settlements to some communities to pay for filtering TCP out of water supplies, but dozens more cases are pending.

Dow and Shell “should have taken it out and disposed of it properly as a toxic waste. But that would have cost them a lot of money, so they left it in and continued to sell these pesticides to farmers throughout California,” said Asha Kreiling, an analyst with the Community Water Center, which along with Clean Water Action has pushed the state to set a legal limit.

“This is an outrageous story of how Shell and Dow essentially got farmers who bought the pesticide to pay to help them get rid of a hazardous waste,” said Bill Walker, EWG’s managing editor and co-author of the report. “How many other hidden examples are there of chemical companies endangering communities through toxic deception?”

Read the full story on EcoWatch.