World’s Largest 1,4-Dioxane Treatment Initiative

Communities on Long Island in New York State rely on extracting groundwater for most of their drinking water supply. Generally considered a clean source of water void of contaminants, United States Environmental Protection Agency (USEPA) regulations still require groundwater supplies to be routinely monitored, and water providers report any detections of biological or chemical contaminants above their regulated maximum contaminant level (MCL). 1,4-Dioxane is not a nation-wide regulated contaminant and does not have an established MCL recognized by the USEPA. Therefore, at the federal level in the U.S., remedial action when detecting 1,4-dioxane in groundwater is not considered mandatory.

However, as early as 2010, water providers on Long Island have been aware of the presence of 1,4-dioxane in local aquifers and began considering countermeasures, but little was known about how widespread the contamination was. In 2017, the USEPA released results from its third Unregulated Contaminant Monitoring Rule (UCMR3) that required public water facilities across the United States to monitor for 28 contaminants, including 1,4-dioxane, which did not have federally regulated MCLs. It was determined that likely due to improper disposal by various industries, approximately 70% of wells extracting groundwater for public supply on Long Island contained 1,4-dioxane above the minimum reporting limit (>0.07 ppb) designated by the USEPA. Further, approximately 25% of tests showed levels above 0.35 ppb, the concentration stated by the USEPA to provide a 1 in 1,000,000 cancer risk in drinking water. The New York State Department of Health (NYSDOH) in response established a Drinking Water Quality Council which recommended a state-wide enforced MCL of 1 ppb in drinking water. This MCL became state law in July 2020 but with the knowledge of widespread 1,4-dioxane contamination, water providers on Long Island had already acted.