Causation Expert WitnessesThe plaintiff sought review of a court of appeals decision affirming the circuit court’s grant of summary judgment dismissing his claims against the Village for negligence and private nuisance. He sued the Village after wastewater backed up into his basement. 

Plaintiff claimed that the court of appeals erred in determining that the Village was immune from suit for negligence pursuant to Wis. Stat. § 893.80(4). He also contended that the court of appeals erred in affirming the grant of summary judgment on his private nuisance claim on the grounds that he failed to present expert testimony on causation. Specifically, Plaintiff argued that the Village’s oral policy to pump water out of a lift station when it reached a certain level created a ministerial duty to act. Plaintiff also said that expert testimony wasn’t required to establish the requisite causation to maintain his private nuisance claim. 

The circuit court granted summary judgment to the Village, and the court of appeals affirmed the circuit court, concluding that the Village was entitled to governmental immunity under state statute. That court held that the Village’s fourth rung “rule of thumb” didn’t create a ministerial duty. As to the private nuisance claim, the court of appeals reasoned that because Plaintiff failed to present expert testimony, he failed to raise a genuine issue of material fact that the negligent failure to maintain the wastewater disposal system was the legal cause of his damages. 

Judge Ann Walsh Bradley of the Wisconsin Supreme Court addressed the necessity of expert testimony to establish that infiltration of water from outside sources caused the backup in Pinter’s basement. The judge noted that a showing of negligence requires proof of causation, and the party with the burden of proof on an element must establish that theres a genuine issue of fact by submitting evidence setting forth specific facts material to that element, citing an earlier case. 

Before expert testimony is held to be required to prove causation, the must determine that the matter isnt within the realm of ordinary experience and lay comprehension. 

Expert testimony, the judge wrote, is often required when unusually complex or esoteric issues are before the jury because it serves to assist the trier of fact,” quoting a 2010 state supreme court case. But if the matter is one of common knowledge or within the realm of ordinary experience, expert testimony isn’t required.  

Judge Bradley explained that expert testimony in the specific context of a municipal sewer system was addressed by the Wisconsin court of appeals in Menick v. City of Menasha (1996). In that casethe court of appeals determined that the municipality wasn’t immune from suit for private nuisance based on negligent failure to maintain the system. However, even though there existed a cause of action in private nuisance, Menick’s failure to offer an expert’s opinion as to the legal cause of the flooding defeats her claim. Specifically, the Menick court concluded: 

Menick has the burden of proving that the flooding was caused by the negligence of the City. Our review of the record shows that she has failed to provide any expert testimony or to advance any theory of liability supported by specific allegations of negligent actions on the part of the City. 

Similarly here, Judge Bradley found that Plaintiff failed to present expert testimony to demonstrate that the Village’s failure to maintain the wastewater disposal system caused water from outside sources to infiltrate the system, thereby causing the backup in his basement. Like the claim at issue in Menick, such a deficiency was fatal to Plaintiff’s nuisance claim. 

As the Wisconsin Supreme Court observed in Milwaukee Metropolitan Sewerage District v. City of Milwaukee, “a negligence-based nuisance requires proof of causation, which may require expert testimony if falling outside the realm of ordinary experience and comprehension. 

Judge Bradley opined that the nuances and complexities of storm water infiltration into the municipal sewer system at issue in this case are outside the realm of ordinary experience and lay comprehension. 

Judge Bradley noted the reasoning of the court of appeals, which stated, [d]etermining to what extent the backup was caused by infiltration, as opposed to Village employees’ failure to bypass, does not fall within the realm of lay knowledge. This kind of determination would require a jury to determine whether water infiltrated the system, if so how much water infiltrated the system, whether the amount was unreasonable, and whether the infiltration contributed to the backup. Because these matters are beyond ordinary experience and lay comprehension, expert testimony is required, the judge stated. 

Without expert testimony, Plaintiff failed to raise a genuine issue of material fact as to whether infiltration by water outside the Village wastewater treatment system caused the wastewater backup in his basement. Pursuant to the facts of this case, expert testimony was required to raise a genuine issue of material fact as to causation. 

The supreme court concluded that the oral policy didn’t rise to the level of a ministerial duty. The proffered “rule of thumb” isn’t “absolute, certain and imperative, involving merely the performance of a specific task when the law imposes, prescribes and defines the time, mode, and occasion for its performance with such certainty that nothing remains for judgment or discretion.” Because such a task is discretionary, the court held that the Village was immune from suit for negligence. 

Further, the court held that the circuit court properly granted summary judgment to the Village on Plaintiff’s private nuisance claim. Pursuant to the facts of this case, expert testimony was required to raise a genuine issue of material fact as to causation. 

The decision of the court of appeals was affirmed.