Why 1,4-dioxane is harder to treat than PFAS — and what that means for NJ water systems

Published by NJ Clean Stream  |  1,4-Dioxane Series, Article 3 of 3

Among water treatment professionals, there is a growing recognition that 1,4-dioxane presents treatment challenges more difficult than those posed by PFAS. This is not widely understood by the public, elected officials, or even many water utility managers. Understanding those challenges should motivate both immediate investment in source control and advance planning for treatment infrastructure — before the contamination that is already developing in New Jersey’s groundwater reaches residents’ taps.

The activated carbon problem

Granular activated carbon (GAC) filtration is the most widely deployed treatment technology for organic contaminants in drinking water. GAC works by passing water through a bed of activated carbon granules to which organic contaminant molecules adsorb, removing them from the water. It is effective against a wide range of contaminants — many chlorinated solvents, certain PFAS compounds, trihalomethanes, pesticides.

Many New Jersey water utilities have invested in GAC systems to address PFAS or other organic contaminant concerns. Water utility managers who understand their systems have GAC may reasonably believe they are protected against organic contaminants. This belief does not extend to 1,4-dioxane.

1,4-dioxane adsorbs very poorly to activated carbon. Its small molecular size, high water solubility, and low tendency to partition out of water make it fundamentally resistant to the adsorption mechanism GAC relies on. Studies consistently demonstrate GAC removal efficiencies of less than 20 percent for 1,4-dioxane under typical drinking water treatment conditions. Water utilities with GAC for PFAS have not thereby protected their customers from 1,4-dioxane. These are independent treatment challenges requiring different solutions.

What does work: advanced oxidation processes

The treatment technology that has demonstrated effective removal of 1,4-dioxane from drinking water is the advanced oxidation process, or AOP. Rather than capturing contaminant molecules on a surface, AOPs destroy them through chemical oxidation using highly reactive hydroxyl radicals that attack and break apart organic molecular structures.

UV/hydrogen peroxide (UV/H₂O₂)

Water is treated simultaneously with ultraviolet light and hydrogen peroxide. The UV light causes hydrogen peroxide to decompose into hydroxyl radicals, which then react with and destroy 1,4-dioxane molecules. UV/H₂O₂ is currently the most widely deployed AOP for 1,4-dioxane treatment in drinking water systems. It is effective, well-understood, and commercially available. Properly designed systems achieve greater than 90 percent removal of 1,4-dioxane.

Ozone/hydrogen peroxide (O₃/H₂O₂)

Ozone and hydrogen peroxide are combined to generate hydroxyl radicals through a different reaction pathway. Used at some large utilities as part of integrated treatment trains that include ozonation for other purposes.

Photocatalytic oxidation

Emerging technologies using semiconductor photocatalysts — typically titanium dioxide — activated by ultraviolet or visible light to generate reactive oxygen species that destroy contaminants. Still largely in research and pilot stages but showing promise for certain configurations.

Why AOP is more expensive than conventional treatment

Capital costs for UV/H₂O₂ systems are significant. A full-scale system capable of treating a medium-sized utility’s source water requires UV reactors (high-intensity UV lamp arrays in stainless steel reactor vessels), chemical storage and dosing systems for hydrogen peroxide, control systems, and integration with the existing treatment train. Capital costs for a system serving a community of 10,000 to 50,000 people might range from several million to tens of millions of dollars.

Operating costs are driven primarily by energy consumption (UV lamps require substantial electrical power) and hydrogen peroxide consumption (continuously replenished). Ongoing operating costs can be several hundred thousand to over a million dollars per year for a community-scale system.

Water quality challenges increase costs. The efficiency of UV/H₂O₂ is significantly affected by background water quality. Water with high concentrations of natural organic matter, iron, carbonate, or other hydroxyl radical “scavengers” requires higher UV doses and more hydrogen peroxide to achieve the same 1,4-dioxane removal — because the scavengers compete with 1,4-dioxane for available hydroxyl radicals. New Jersey groundwater from many aquifer systems has characteristics that reduce AOP efficiency and increase costs.

Post-treatment management. UV/H₂O₂ treatment generates oxidation byproducts — transformation products formed when hydroxyl radicals react with 1,4-dioxane and other organic compounds in the water. Some byproducts require monitoring and may require additional treatment steps.

The monitoring gap: you can’t treat what you haven’t measured

Before a utility can address 1,4-dioxane, it must know it is there. Standard analytical methods for 1,4-dioxane in water require EPA Method 522 — a specialized procedure using solid-phase extraction followed by gas chromatography/mass spectrometry. This method is not included in the routine compliance monitoring panels that New Jersey utilities must conduct under the Safe Drinking Water Act. Without a federal MCL for 1,4-dioxane, it is not on the list of contaminants utilities are required to monitor.

The result: most New Jersey water utilities serving groundwater or groundwater-influenced surface water have simply never measured 1,4-dioxane in their source water or finished water. They don’t know whether it is present, at what concentration, or whether it is trending upward as contaminated groundwater plumes migrate toward their supply wells. This monitoring gap is not acceptable given what we know about the industrial footprint of 1,4-dioxane contamination in New Jersey.

What New Jersey needs to do: a treatment and regulatory roadmap

  • Establish a New Jersey MCL for 1,4-dioxane. The NJ DEP has authority under the NJ Safe Drinking Water Act, independent of federal regulation. New York has set 1 ppb; Connecticut 3 ppb. New Jersey should establish an MCL at or below 1 ppb — consistent with EPA’s one-in-one-million cancer risk benchmark — with immediate notification requirements if source water exceeds the MCL.
  • Mandate statewide source water monitoring. All community water systems should be required to test source water for 1,4-dioxane using Method 522, with results reported to the NJ DEP and disclosed to the public. Annual monitoring at minimum; more frequent for utilities near identified 1,4-dioxane source sites.
  • Require 1,4-dioxane assessment at all active contaminated sites. The NJ DEP’s Site Remediation Program should require 1,4-dioxane characterization at all sites with documented chlorinated solvent contamination, including sites with existing remediation approvals that predate recognition of 1,4-dioxane as a co-contaminant.
  • Invest in AOP treatment infrastructure. State and federal infrastructure funding should be available to utilities that need to install advanced oxidation treatment. Priority for utilities near known 1,4-dioxane source sites and smaller utilities lacking financial capacity to fund AOP installation independently.
  • Pursue cost recovery aggressively. When 1,4-dioxane in a water supply can be traced to an identifiable industrial source, the NJ DEP and affected utilities should pursue cost recovery from responsible parties for the full cost of source investigation, treatment installation, and ongoing operation.

What the failure to act will cost

PFAS contamination provides the cautionary lesson: communities exposed for years before contamination was discovered and remediation required now face cleanup costs, health monitoring programs, and legal proceedings vastly more expensive than early action would have been. 1,4-dioxane is at the point where early action is still possible. The contamination exists. The source sites are known categories. The treatment technology exists. The regulatory authority exists. The scientific basis for setting a health-protective MCL exists.

What does not yet exist is the political will — driven by an informed public demanding action — to move the NJ DEP from awareness to regulation. NJ Clean Stream is committed to creating that political will. New Jersey can do better. It has done better — on PFAS, on lead pipes, on other water quality issues where advocacy, science, and regulatory will converged. The case for doing better on 1,4-dioxane is exactly as strong. The time to act is now.

This is Article 3 of 3 in NJ Clean Stream’s 1,4-Dioxane Series. Article 1 introduces the chemical, its health risks, and the regulatory gap. Article 2 examines the industrial sites responsible for NJ’s contamination and the cost recovery framework.