Sydney Mine Sludge Ponds

Overview

Sydney Mine Sludge Ponds sits in Brandon, Florida, and carries final National Priorities List (NPL) status, meaning the EPA considers it among the nation's most hazardous sites. The property was used for phosphate mining from the 1930s through the 1950s, then served as a liquid waste disposal facility until 1981. Past disposal practices contaminated soil, sediment, and groundwater, including the Hawthorn Aquifer, the principal local drinking water source. Contaminated groundwater spread a few hundred feet beyond the site boundary but remains contained within the mining area.

EPA has identified nine contaminants of concern, all found in groundwater. They include volatile organic compounds (VOCs) and solvents: benzene, toluene, ethylbenzene, chlorobenzene, vinyl chloride, 1,1,1-trichloroethane, 1,1-dichloroethane, 1,1-dichloroethene, and 1,2-dichloroethane. The Agency for Toxic Substances and Disease Registry (ATSDR) maintains additional health effects information for each of these chemicals.

Cleanup began in 1982 with a slurry wall and a groundwater pump-and-treat system. Contaminated soils were excavated from 1987 to 1989, and a formal remedy was approved in September 1989, then modified in 1991 to address VOCs in the upper aquifer. The pump-and-treat system was shut down in 1997 after natural attenuation proved effective. Physical construction across the site was completed in June 1999. The site is now in long-term operations and maintenance, carried out by the responsible parties. The groundwater plume is stable and shrinking, with concentrations steadily decreasing. Semi-annual sampling tracks benzene, vinyl chloride, and 1,4-dioxane levels. Hillsborough County plans to install additional monitoring wells between 2024 and 2025 to better map 1,4-dioxane contamination. The 2021 Five-Year Review confirmed the remedy remains protective of human health and the environment, and the most recent Five-Year Review was completed in April 2026. The site has not yet been deleted from the NPL.

A restrictive covenant prohibits groundwater use at the site and prevents any residential development. People living nearby are far from the contaminated groundwater, and human exposure is under control. The site achieved a status of "sitewide ready for anticipated reuse" in July 2017, and an investment group has purchased the property with plans to develop it as an alternative energy park converting algae into fuel.

Community members can review site records at Brandon Library, located at 619 Vonderburg Drive in Brandon, Florida. A Question-and-Answer Fact Sheet is available to address common questions. The EPA holds public notices and meetings to share updates and gather community input.