Utilities Engineering


About 1,4-Dioxane

1,4-dioxane (1,4-d) is a manufactured chemical that can occur as a colorless, flammable liquid that easily dissolves in water. It has been used as a stabilizer for solvents and cleaners and is present in many goods, including paint strippers, dyes, greases, antifreeze, and aircraft deicing fluids. 1,4-dioxane has been identified as a contaminant of concern as it can remain in the groundwater for an extended period. It remains an unregulated contaminant; drinking contaminated water is the most common way people encounter 1,4-dioxane.

Health Advisory Levels (HAL) for 1,4-dioxane were established in 2012 by the Environmental Protection Agency (EPA) at 0.35 parts per billion (ppb). Before this time, health standards were not set by the EPA, the Florida Department of Health (FDOH), or the Florida Department of Environmental Protection (FDEP). Florida adopted the EPA’s Health Advisory Level in December 2015; FDEP is responsible for enforcing state-regulated levels for 1,4-dioxane in groundwater, surface water, and soil per Florida Administrative Code. 

Please note, for information regarding Total Trihalomethanes (TTHM), please visit seminolecountyfl.gov/tthm.

Seminole County’s Water Utility 

Safeguarding Seminole County’s drinking water is of the highest importance to the Board of County Commissioners and County staff. The County’s potable water systems are sampled and tested for contaminants based on monitoring requirements established by the Florida Department of Environmental Protection. 

In April 2023, the Florida Department of Environmental Protection collected samples at three Heathrow wells. All test results for 1,4-dioxane were below the EPA’s health advisory level of 0.35 ppb. Levels of 1,4-dioxane at the County’s Markham Regional Water Treatment Plant have averaged 0.18 ppb since 2016. In May 2023, internal sampling of all potable water systems at the point of entry confirmed minimal-to-no detection of the contaminate. 

In order to ensure concentrations of 1,4-dioxane are minimized in County drinking water, well production schedules have been modified, and the sampling range has been increased. Staff has engaged a consultant to assist with developing short-and-long-term plans to address internal protocols and processes related to sampling, monitoring, and reporting. In July-August 2023, Environmental Services staff members will begin collecting samples from all 25 potable wells within the County’s Water Service Area, and the points of entry for all five potable water systems, on a monthly basis. 

The County relies on state and federal regulators to research and adopt protective standards. Staff continues to work with FDEP to coordinate sampling, assessment, and remediation activities. 

More Information About 1,4-Dioxane

Seminole County Annual Drinking Water Quality Reports by Year


Video: 1,4-Dioxane Presentation at Board of County Commissioners Meeting, 7/25/23

Feedback Form

Contact Us

For more information regarding 1,4-dioxane, please call Environmental Customer Service at 407-665-2110 or email dioxane@seminolecountyfl.gov.