A Delaware court this week began hearing a dispute between DuPont and its former chemicals business Chemours over liabilities for payouts connected to spills of fluorochemicals into US waterways.

DuPont is asking the court to dismiss a lawsuit from the company spun off in 2015 that claims it massively downplayed the cost of environmental liabilities Chemours would face after separation from the former parent.

Both companies are based in Wilmington, Delaware. DuPont says the lawsuit must be dismissed because the separation agreement mandates that disputes arising from the 2015 spinoff must be resolved through private arbitration.

DuPont also rejects Chemours’ allegation that it deliberately spun off the business to shift hundreds of millions of dollars in environmental liabilities to it.

At the time of the spinoff, prior to DuPont’s merger into DowDuPont – from which it emerged earlier this year – the then-broadly focused chemical producer was facing multidistrict litigation involving 3,500 personal injury claims related to the fluorochemical PFOA, used in production of the Teflon-branded non-stick coating.

Chemours’ lawyers want the judges to declare that the company is not responsible for liabilities exceeding the maximums certified by DuPont or any of its historical liabilities exceeding the cap. Alternatively, it is asking that the $3.9 billion dividend it paid DuPont at the time separation be returned.