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EPA proposes taking Tybouts Corner, Chem-Solv off Superfund list


The U.S. Environmental Protection Agency has proposed deleting a portion of the Tybouts Corner Landfill in New Castle snf the Chem-Solv, Inc. Site in Cheswold from the Superfund National Priorities List (NPL).

The NPL is a list of the nation’s most contaminated hazardous waste sites. from the Superfund National Priorities List (NPL). The NPL is a list of the nation’s most contaminated hazardous waste sites.


Delaware has nearly two dozen such sites. In the early 1980s, Tybouts Corner was listed as one of the 10 worst waste dumping sites by the EPA

EPA deletes sites or parts of sites from the NPL when no further cleanup is required to protect human health or the environment.

“Deleting sites from the NPL is a major milestone for Superfund impacted communities,” said EPA Mid-AtlanticRegional Administrator Adam Ortiz.  “An NPL deletion, and even a portion of a site, signals that cleanup is complete and the site no longer poses a threat to public health and the environment.”

The Tybouts Corner Landfill Site is in New Castle County,  approximately 10 miles south of Wilmington and four miles west of the Delaware River.

The site was used by the New Castle County Department of Public Works as a municipal sanitary landfill which accepted industrial wastes from December 1968 until July 1971. The landfill consisted of two non-adjoined sections, a West Landfill that was about four acres and the Main Landfill that was about 47 acres, with waste ranging from five to 40 feet thick. Contamination was found in two nearby wells in 1976 and again in 1983.

The site is being addressed through federal and Potentially Responsible Party (PRP) actions.  Based on cleanup activities, soil, and groundwater monitoring data, and no existing waste remaining on-site, EPA has determined that actions are complete for the two parcels on Tybouts Corner Landfill and have been proposed for partial deletion from the NPL.

EPA also negotiated several Consent Decrees with numerous companies to perform the remedial design and remedial action. The remedy included:

  • The material in the West Landfill was excavated and consolidated with the waste in the Main Landfill.
  • A groundwater pumping system consisting of eight extraction wells was installed to contain contaminated groundwater at the landfill.
  • A subsurface slurry wall, a subsurface barrier that impedes or stops groundwater flow, was installed to prevent clean groundwater from entering the landfill.
  • A multi-layer cap was constructed to prevent rain from entering the waste material in the landfill.
  • A (passive) venting system was installed to prevent the build-up of landfill gases within the landfill, which uses existing variations in landfill pressure and gas concentrations to vent landfill gas into the atmosphere.

In 1996, a temporary active gas venting system was installed in the Main Landfill portion of the Site due to detection of landfill gas outside the boundaries of the landfill. In 2000, a permanent active gas venting system was installed. The active gas venting system is designed with vacuums or pumps to move gas out of the landfill and is effective in preventing the migration of underground landfill gas beyond the landfill property boundary. Annual monitoring of the passive landfill gas vents continues.

In May 2007, contaminant concentrations in groundwater decreased significantly and EPA and the Delaware Department of Natural Resources and Environmental Control (DNREC) agreed to shut down the pumping wells. In 2008, quarterly monitoring of the groundwater ceased, and the wells are now sampled semi-annually.  A Groundwater Management Zone established by the State of Delaware that restricts groundwater use will remain in place for the Main Landfill portion of the site until determined unnecessary.

While significant progress has been made in the clean-up of the Main Landfill portion of the Tybouts Corner site, all performance standards have not yet been achieved and it will remain on the list.

EPA published a Federal Register Notice on March 31 proposing to delete all or part of 10 sites from the NPL. There will be a public comment period through May 2. The agency plans to publish another notice with additional final and proposed deletions this fall.

The Chem-Solv, Inc. site is located on a 1.5-acre property in Cheswold in Kent Couty. Chem-Solv was a small solvent distillation facility dating from 1982.

The facility recycled waste solvents, but in 1984 an explosion and fire at the site destroyed the facility. After the fire, authorities evaluated the Columbia Aquifer beneath the site and found high concentrations of volatile organic compounds (VOCs), primarily trichloroethene (TCE).  TCE is a heavy colorless highly toxic liquid used as a solvent to clean electronic components and for dry cleaning.

Groundwater recovery and treatment was conducted from 1997-2017. In 2017, groundwater sampling showed concentrations had dropped below cleanup levels and groundwater extraction and treatment were conditionally discontinued.

EPA has conducted several five-year reviews of the site’s remedy. The most recent, 2018 Five-Year Review (PDF), concluded that the remedy continues to be protective of human health and the environment.  A Groundwater Management Zone established by the State of Delaware that restricts groundwater use will remain in place until determined unnecessary.

Based on monitoring data collected, EPA determined that the response at the Chem-Solv Site is complete and as a result, the Site has been proposed for deletion from the NPL.