Maunabo Area Ground Water Contamination

Overview

The Maunabo Area Ground Water Contamination site sits in southeastern Puerto Rico. Chlorinated solvents polluted the groundwater that feeds four public supply wells serving roughly 14,000 residents. EPA added the site to the National Priorities List in September 2006. A final cleanup plan was chosen in September 2012, remedial design finished in February 2018, and construction wrapped up in April 2023.

Four contaminants are present in the groundwater: 1,1-dichloroethene, vinyl chloride (also called chloroethene), cis-1,2-dichloroethene, and tetrachloroethene (PCE). Testing found three separate contaminated plumes. The cis-1,2-dichloroethene plume had the highest levels. The PCE plume was very dilute. The 1,1-dichloroethene plume was more spread out. EPA determined all four chemicals pose an unacceptable risk to human health or the environment.

In March 2002, the Puerto Rico Department of Health ordered one well, Maunabo #1, to close because PCE exceeded the federal safety limit of 5 micrograms per liter. Instead of closing it, the Puerto Rico Aqueduct and Sewer Authority installed activated carbon filtration at the wellhead. The 2012 cleanup plan used air sparging, which forces air through contaminated water to drive off harmful chemicals, to treat the worst plume. The two more dilute plumes were left to monitored natural attenuation, meaning contaminants degrade or dilute on their own while the site is regularly sampled. Air sparging work ran from November 2020 through March 2021. Confirmation sampling showed volatile organic compound levels in monitoring wells had dropped below federal safety limits. Quarterly sampling continued through 2023.

Human exposure is currently under control, with no unacceptable exposure pathways identified. Contaminated groundwater migration has been stabilized, and no unacceptable discharge to surface water is expected. EPA is now managing long-term response actions that began in September 2023. The site is estimated to be ready for anticipated reuse between October and December 2027. A five-year review is scheduled for April through June 2028.

Community members can contact the EPA staff assigned to the site. Records related to the site are available at the EPA Region 2 Superfund Records Center in New York, the EPA Division of Environmental Protection of the Caribbean in Guaynabo, Puerto Rico, the Environmental Quality Board in San Juan, Puerto Rico, and at Maunabo City Hall.