The U.S. Environmental Protection Agency on Sept. 30 signed off on a final groundwater remedy for the Chemsol Inc. Superfund site in Piscataway, New Jersey, selecting long-term monitoring and groundwater use restrictions over engineered treatment for an off-site plume that migrated from the former Fleming Street solvent recovery facility decades ago.

The decision, formalized in the agency's record of decision for the site, applies to contaminated groundwater that moved beyond the property boundary before hydraulic controls were installed. EPA concluded that monitored natural attenuation — relying on naturally occurring biological and chemical processes — will continue breaking down residual solvent contamination, with monitoring data already showing declining contaminant concentrations in the off-site plume.

For a site that processed industrial solvents through mixing, blending, distilling and recovery operations, the remedy closes out the last major unresolved media at the Middlesex County site. Contaminated soil and sediment have already been excavated and removed. Groundwater beneath the site itself remains under active treatment through an existing cleanup system designed to prevent further off-site migration of pollutants. The newly finalized plan covers only what slipped past those controls historically.

"Today's announcement marks a significant step in addressing residual contamination at the Chemsol Inc. Superfund site," EPA Regional Administrator Michael Martucci said in a statement announcing the decision.

The final plan carries two operational obligations: long-term groundwater monitoring and institutional controls restricting groundwater use within the affected area until contaminant levels fall to acceptable thresholds. EPA will track attenuation rates against cleanup standards over time, a schedule that effectively defines the site's remaining lifecycle in the Superfund program.

The agency identified no current exposure pathway to drinking water. Homes and businesses near the site connect to public water systems regulated and routinely tested under the Safe Drinking Water Act, eliminating direct domestic reliance on the affected aquifer.

The path to the final remedy ran through a compressed public process. EPA opened a 30-day comment period and hosted a virtual public meeting on Aug. 26. The comment window closed Sept. 11 with no submissions received, clearing the way for the agency's Sept. 30 decision without modification.

Chemsol's history tracks the arc of the solvent recovery industry's legacy liabilities in the industrial corridor of central New Jersey. The facility handled solvent reprocessing and waste recovery operations before contamination was identified in soil, sediment and groundwater, triggering listing in the federal Superfund program. EPA has overseen remediation at the property for decades, progressing from source removal to containment to, now, passive management of the residual dissolved-phase plume.

The selection of natural attenuation over pumped treatment for the off-site plume carries cost and operational implications worth noting. Monitored natural attenuation eliminates capital expenditure on additional extraction and treatment infrastructure for the exterior plume, substituting sampling and analysis obligations that will persist until contaminant concentrations meet remediation goals. The existing on-site treatment system continues operating independently.

What happens next turns on monitoring performance. EPA will continue tracking groundwater conditions at the site to confirm the remedy remains protective of public health and the environment, and attenuation must demonstrate sustained contaminant decline for the restrictions on groundwater use to eventually lift. Absent that trajectory, the agency would face renewed evaluation of active treatment options for the plume.

The Sept. 30 record of decision now stands as the operative regulatory milestone at Chemsol — the document that determines the monitoring regime, the use restrictions and the yardstick against which EPA will measure the site's eventual readiness for deletion from the National Priorities List.