Diamond Alkali, a chemical company in Newark, dumped Agent Orange and other chemicals into the Passaic River, creating a toxic mess that is now one of the nation’s largest Superfund sites.

In early March, the EPA ordered Occidental Chemical Corporation, or OxyChem — the company that bought Diamond Alkali — to start planning remediation for nine miles of the Passaic River. OxyChem is now pushing to defeat a pending legal agreement, potentially leaving New Jersey taxpayers to pay the $1.82 billion bill for the cleanup of the Passaic.