Rainfall and groundwater fluctuations may influence the migration or dilution of contaminants from US Superfund sites. This pilot study was designed to provide empirical data on relationships between rainfall and contaminant concentrations in water near Superfund sites. Four heterogeneous Superfund sites on Long Island, New York, were selected to represent a range of contaminant profiles and hydrogeologic conditions. Baseline samples were collected in December 2022, with subsequent samples obtained following major storms through September 2023. Samples were collected on 11–24 different days across the sites and measured for 18 metals and 1,4-dioxane. Overall, we observed few consistent associations between rainfall and contaminant concentrations across sites. Two trends, however, were noted: (1) at Gowanus Canal, a surface water site, there was a negative association between rainfall and contaminant concentrations using same-day or prior-day rainfall; and (2) in effluent from a treatment well near Lawrence Aviation, negative associations were observed between prior month’s rainfall and contaminant concentrations. Rainfall appeared to dilute contaminant concentrations using different hydrogeological processes at two of the four Superfund sites in this pilot study with a small sample size and study site heterogeneity. Given the increased frequency and intensity of extreme rainfall events, it is important to continue probing links between rainfall and contaminants near Superfund sites with intensive monitoring campaigns.

Rainfall and groundwater fluctuations may influence the migration or dilution of contaminants from US Superfund sites. This pilot study was designed to provide empirical data on relationships between rainfall and contaminant concentrations in water near Superfund sites. Four Superfund sites on Long Island, New York were selected to represent a range of contaminant profiles and hydrogeologic conditions. Baseline samples were collected in December 2022, with subsequent samples obtained following major storms and seasonally through September 2023. Samples were collected on 11–24 different days across the sites and measured for metals and 1,4-dioxane. Overall, we observed few consistent associations between rainfall and contaminant concentrations across sites. Two trends, however, were noted: (1) At Gowanus Canal, a surface water site, there was a negative association between rainfall and contaminant concentrations using same-day or prior-day rainfall; and (2) in a treatment well near Lawrence Aviation, negative associations were observed between prior month’s rainfall and contaminant concentrations. Rainfall appeared to dilute contaminant concentrations at two of the four Superfund sites. Given the increased frequency and intensity of extreme rainfall events, it is important to continue probing links between rainfall and contaminants near Superfund sites.