Hocomonco Pond

Overview

A wood-treating facility ran at the Hocomonco Pond site in Westborough, Massachusetts from 1928 to 1946. The site covers 23 acres and has been on the EPA's National Priorities List (NPL) since September 8, 1983. Physical construction of the cleanup finished on September 22, 1999, and the site achieved Sitewide Ready for Anticipated Use status on December 5, 2017. That status means all cleanup goals for current and reasonably expected future land uses have been met, required land-use restrictions are in place, and no further actions are needed to address contamination. The site has not yet been deleted from the NPL.

EPA identified 39 contaminants of concern tied to creosote from the former wood-treating operations. These include metals such as arsenic and chromium, volatile organic compounds (VOCs) like benzene, and polycyclic aromatic hydrocarbons (PAHs) including naphthalene, anthracene, pyrene, and benzo[a]pyrene. Contamination is found in groundwater (19 contaminants), soil (21), surface water (18), and sediment (18).

Cleanup has included building a double-lined landfill completed in 1996, capping a former lagoon, and removing sediment. A groundwater treatment plant ran from 1994 to 2003 to recover Dense Non-Aqueous Phase Liquid (DNAPL), a heavy contaminant that sinks below the water table. Since 2003, DNAPL has been manually removed every three months (except winter) from above the bedrock and disposed of off-site, averaging about 37 gallons per month. The persistence of the DNAPL pool means full groundwater cleanup is not technically feasible. Institutional controls restrict land use to prevent residential and other incompatible uses, and these controls stay in place as long as contamination or cleanup components remain on site.

Human exposure is under control, with no unacceptable pathways for people to contact contamination. Groundwater migration is also under control, with no unacceptable discharge to surface water. EPA's most recent Five-Year Review, completed August 20, 2024, confirmed the remedy remains protective. It recommends continued monitoring of sediment and groundwater to meet ecological goals targeting total PAH and phenanthrene sediment levels. The next Five-Year Review is scheduled for 2029.

Community members with questions about land-use restrictions or cleanup activities can contact EPA directly using the information below. Site documents are available at EPA's Region 1 office in Boston and at the Westborough Public Library at 55 West Main Street. Additional information is at www.epa.gov/superfund/hocomonco.