This case arises out of the contamination of surface waters and drinking water in Chattooga County, Georgia, with per- and polyfluoroalkyl substances known as “PFAS.”
In essence, Plaintiff Earl Parris, Jr., alleged that the Defendants have contaminated his city’s water supply and thus his household water with PFAS. Parris is a resident of Summerville, Georgia, who receives running, potable water to his home from the Summerville Public Works and Utilities Department.
The City of Summerville—which has intervened in this case—used Raccoon Creek, a tributary of the Chattooga River, as the main source of its municipal water supply. The Defendants are the following companies, which allegedly manufactured and supplied the PFAS discharged into Raccoon Creek: 3M Company (“3M”), Daikin America, Inc., E.I. du Pont de Nemours and Company, and The Chemours Company. Parris alleged that Raccoon Creek and—consequently, his household water—have been contaminated with PFAS by the Defendants. PFAS can allegedly cause adverse health effects such as kidney and testicular cancer.
Parris and Summerville have jointly moved to exclude the testimony of defense expert Laurentius Marais under Federal Rules of Evidence 702 and 403.
Statistics Expert Witness
Marthinus Laurentius Marais is a consultant specializing in applied mathematical and statistical analysis. He holds graduate degrees in mathematics, statistics and business administration from Stanford University. At the Stanford Graduate School of Business he received a PhD degree for a dissertation on applications of computer-intensive statistical methods to quantitative analyses of topics in business. He has served on the faculties of the University of Chicago and Stanford University.
Discussion by the Court
Marais’ expert report examined kidney and testicular cancer rates in counties with and without high PFAS levels in the water supply, including in Chattooga County, and concluded that there is “no statistically detectable, empirically significant indication of an association” between those cancer rates and PFAS exposure.
A. Relevance
The Plaintiffs contended that Marais’ conclusions regarding the lack of association between PFAS and cancer are irrelevant because this lawsuit is based on the city’s drinking water being out of compliance with the EPA’s PFAS limits, not based on personal injury damages from health costs.
However, the Court agreed with the Defendants that Marais’ opinions are relevant.
First, the Plaintiffs conceded that evidence regarding whether PFAS “can” cause cancer is relevant to this litigation, and Marais’s opinions may help a jury answer this question. Marais’ opinions compare cancer and PFAS statistics across counties in the United States, not just in Chattooga County.
The Court is not persuaded by the Plaintiffs’ distinction between “general causation” evidence and “specific causation” evidence. That Marais’ opinions on PFAS and cancer included data from Chattooga County, where Summerville residents reside, is not grounds for excluding the opinions altogether.
Second, the Plaintiffs’ extensive allegations of PFAS’ health risks are material to the relevance question. The Plaintiffs explicitly relied on such allegations in their claims for negligence (Counts V, VII), wanton conduct and punitive damages (Count VIII), and public nuisance (Count IX). Evidence that health risk never materialized is therefore relevant to the Defendants’ liability on those claims. For example, weighing testimony about the nonexistent association between PFAS and cancer in the Plaintiffs’ geographic area may help a jury evaluate whether the Defendants were negligent for manufacturing or failing to warn about PFAS in the first place.
B. Reliability
The Plaintiffs took issue with four aspects of Marais’ testimony: (1) it misinterpreted the underlying data, which Plaintiffs argue shows above-average testicular cancer rates despite below-average rates for all other types of cancer; (2) it compared county-level cancer data with city-level PFAS exposure data, which weakens the PFAS–cancer association in the case of Summerville because Chattooga County receives only about 20% of its drinking water from Summerville; (3) it is underinclusive because it did not account for latency effects, such as when a Summerville resident moves to a different county and develops cancer decades later; and (4) it is underinclusive because it did not include data from neighboring states where Summerville residents may have sought cancer treatment (e.g., at a Tennessee cancer center less than one hour’s drive away).
Analysis
The Court held that the methodology underlying Marais’ testimony was reliable. To begin with, any issues with the content of Marais’ conclusions in interpreting his own data are improper considerations at the admissibility stage. The focus of the reliability inquiry is on the expert’s “principles and methodology,” rather than his or her ultimate conclusions.
Second, the county-city mismatch argument that the Plaintiffs identify is better suited for cross-examination than an admissibility challenge. The datasets on which Marais relies are produced by reputable organizations. The cancer data is produced at a county level from the National Center Institute, National Institute of Health, and Centers for Disease Control, and the PFAS data is produced at the public water district level by the EPA.
Lastly, regarding the possibility that Marais’ dataset is underinclusive due to latency and residency problems, this argument too is more appropriate for cross-examination. Other than attempting to identify hypotheticals, the Plaintiffs have not pointed to any evidence that suggests Marais’ datasets depart from standard industry practice.
For these reasons, the Court declined to exclude Marais’ testimony as unreliable. Marais has shown his methodology is sufficiently sound and that it is “properly grounded, well-reasoned, and not speculative.”
C. Prejudice
The Plaintiffs contended that Marais’ testimony will confuse the jury because it would question “(1) where his testimony fits into the City’s case, and (2) why the City has not offered any rebuttal evidence.”
Any jury would understand the importance of introducing evidence on the health consequences of an alleged pollutant in a water pollution case, and the lack of rebuttal evidence is plainly not grounds for exclusion under Rule 403.
Held
The Court denied Plaintiff Earl Parris, Jr., and Intervenor-Plaintiff City of Summerville’s motion to exclude the testimony of Laurentius Marais.
Key Takeaway
Datasets may be imperfect at times, but that is not grounds to render an entire analysis unreliable. The purpose of Daubert is to ensure that an expert “employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.”
Please refer to the blogs previously published about this case:
Polymers Expert Allowed to Opine on PFOS Sources
Geology Expert’s Testimony on Potential Alternative Sources Admitted
Case Details:
| Case Caption: | Parris V. 3M Company |
| Docket Number: | 4:21cv40 |
| Court Name: | United States District Court, Georgia Northern |
| Order Date: | March 13, 2026 |
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