On July 9^th, 2025, the Eastern District of New York ruled on a series of motions in Suffolk County Water Authority v. Dow Chemical Company, a case brought by the Suffolk County Water Authority (“Suffolk”) against chemical manufacturers for the alleged contamination of Suffolk’s groundwater supply with 1,4-dioxane (“dioxane”), a chemical classified by the EPA as a “probable human carcinogen.”  Judge Gershon issued an opinion allowing most of the plaintiff’s common law tort claims to proceed to trial while clarifying the standard for expert admissibility under recently amended Federal Rule of Evidence 702.

Suffolk is a public benefit corporation that provides drinking water to Long Island residents, operating over 580 wells that draw from aquifers in Suffolk County, New York.  In this case, Suffolk brought suit against The Dow Chemical Company (“Dow”), Legacy Vulcan LLC (“Legacy”), and Vibranz Corporation (“Vibranz”), alleging the three companies’ involvement dating back to the 1950s in manufacturing 1,1,1,-trichloroethane (“TCA”), an industrial solvent used in metal degreasing containing dioxane, caused contamination of Suffolk County water supply through ordinary use and disposal of these products.  Suffolk argued that to address the contamination, it must design, construct, and maintain treatment facilities and equipment to remove dioxane from its wells.  Suffolk sought compensatory and punitive damages alongside injunctive relief through New York common law claims for strict products liability and negligence for defective design and failure to warn, trespass, and public nuisance.

The defendants filed a joint motion for summary judgment and a motion to exclude the opinions of several expert witnesses retained by Suffolk under Federal Rule of Evidence 702 (“Rule 702”).  Because exclusion of expert testimony had the potential to impact whether the evidence was sufficient to withstand defendants’ motion for summary judgement, Judge Gershon’s opinion first addressed the 2023 amendments to Rule 702, which clarified that when deciding whether an expert opinion is admissible, trial courts must apply a preponderance-of-the-evidence standard to each of the rule’s four admissibility prongs: the witness is qualified to be an expert, the opinion is based on reliable data and methodology, the opinion reflects a reliable application of the methodology to the facts of the case, and the expert’s testimony on a particular issue will assist the trier of fact.  According to the Federal Rule’s Advisory Committee, this clarification was necessary because many courts had incorrectly held that some of the Rule 702 criteria constituted questions of weight and not admissibility.  Despite the change in Rule 702, the court found nearly all of Suffolk’s expert witnesses testimony was admissible, emphasizing that disputes over methodology and interpretation should typically be addressed through cross-examination at trial rather than exclusion.

The opinion then addressed the defendants’ joint motion for summary judgment, which was granted in part and denied in part. The court dismissed Suffolk’s design defect claims against all defendants, finding that Suffolk failed to provide sufficient evidence that an alternative feasible design was available.  Specifically, the court found that Suffolk had not demonstrated that using 1,3-dioxolane would have been safer than using dioxane stabilized TCA.

With respect to Suffolk’s failure to warn claims against Dow and Vulcan, the court first addressed causation. The defendants argued that Suffolk could not show that Dow and Vulcan’s failure to warn about the risk of their products was a substantial factor in causing Suffolk’s injury, because Suffolk did not provide direct evidence that the dioxane chemicals originated at defendants’ facilities. The court disagreed, holding that Suffolk was not required to show that individual dioxane chemicals originated at Dow or Vulcan; it was enough to show that dioxane contamination within the wells “came from dioxane-stabilized TCA products and that those products were manufactured by Dow and Vulcan.” The court also barred Suffolk from presenting a market share theory of causation in the alternative in the event the jury were to find it did not establish substantial factor causation. Separately, in addressing the adequacy of the warnings themselves, the court found genuine issues of material fact regarding whether the defendants’ warnings about dioxane hazards were sufficient. For that reason, Suffolk’s strict products liability and negligent failure-to-warn claims against Dow and Vulcan survived summary judgment.

Additionally, the court held that Suffolk’s trespass claim could proceed. Defendants argued that Suffolk had no ownership interest in the groundwater itself, which is a natural resource held in trust by the State. The court rejected this argument, citing Benoit v. Saint-Gobain Performance Plastics Corp., 959 F.3d 491, 503, in which the court held that well owners may maintain a trespass action for groundwater contamination because the groundwater is the medium through which the contaminant invades the wells. The court found that Suffolk put forth sufficient evidence of a property interest in each of its wells, whether by leasehold, easement, or ownership.  The court then addressed the appropriate trespass standard, which is whether the defendants (i) intended the act that produced the unlawful invasion, and (ii) had good reason to know or expect that the contaminant would migrate onto the plaintiff’s property. The court found that the record demonstrated that Dow, Vulcan, and Ferro intentionally manufactured, sold, and distributed dioxane and dioxane-stabilized TCA, including in the Suffolk County market, where they instructed end users on its use and disposal. The evidence also showed that each defendant had good reason to know or expect the products would travel to and contaminate Suffolk’s wells, based on their large market share, knowledge of disposal practices, scientific understanding of dioxane’s persistence and mobility, membership in industry groups centered around water pollution, and awareness of the vulnerability of Long Island aquifers to contamination.

Regarding Suffolk’s public nuisance claim, the defendants argued that they could not be held liable because they had no ability to control how end users disposed of TCA. While some jurisdictions require control in public nuisance claims against product manufacturers, New York does not. The court applied New York’s “substantial participation” test, under which a manufacturer’s liability does not depend on control over the end user. Rather participation and control are distinct concepts, and a jury may conclude that a chemical manufacturer substantially participated in creating a nuisance based on its role in manufacturing, supplying, and selling a harmful product even without evidence that it controlled the product’s ultimate disposal.

This case exemplifies the potential viability of state common law claims for public water suppliers seeking to hold chemical manufacturers accountable for legacy groundwater contamination.  Additionally, this decision signals that the recent amendments to Rule 702 may not alter the district court’s “gatekeeping” function for expert evidence as the court found that disputes over environmental expert testimony should typically be addressed at trial.

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