DOE says Santa Susana groundwater pilot is beginning to reduce contaminants

The US Department of Energy says an underground treatment pilot at California’s Santa Susana Field Laboratory is beginning to reduce volatile organic compounds in groundwater. The finding matters because DOE plans to use the pilot’s monitoring data to help design future cleanup work in Area IV. Its September 22 update describes an early result at one small study area, with groundwater samples collected through July 2026.

The public update does not give before-and-after contaminant concentrations, results for individual monitoring wells or an independent evaluation. DOE’s account therefore establishes what the agency says it has observed, but does not allow readers to measure the size or consistency of the reported reduction. The agency says quarterly monitoring will continue to assess how effectively the treatment is working.

How the pilot works

DOE is testing the method in the Hazardous Material Storage Area of Area IV. That part of the 2,850-acre Santa Susana site previously hosted DOE liquid-metals and nuclear-energy research, and the department is responsible for its remediation. DOE ETEC project director Josh Mengers said the study area was chosen because its groundwater conditions and contaminants suited this treatment approach.

The treatment works in place, underground. In September 2025, DOE completed seven injection wells to deliver food-grade emulsified vegetable oil and zero-valent iron below the surface. It also introduced bacteria called Dehalococcoides. According to DOE, the bacteria help degrade volatile organic compounds through biological activity, while the iron provides a separate chemical route for breaking them down.

By July 2026, DOE had collected seven months of groundwater samples from monitoring wells. Mengers said the early findings showed that treatment was performing as expected and beginning to reduce contaminant concentrations. The September update does not identify which compounds fell, give the measured levels or show how results varied among wells. Those details would help establish the extent of the change the agency reports.

What an earlier field test shows

A separate field test offers context for the treatment concept, rather than a measurement of this pilot. In a 2012 study published in Water Research, researchers evaluated emulsified zero-valent iron nanoparticles at Parris Island, South Carolina, over two and a half years. The source zone there was dominated by tetrachloroethene and related chlorinated compounds. The researchers observed lower contaminant concentrations in wells downstream of the injection area and increases in degradation products, including ethene.

In one Parris Island test plot, the researchers reported reductions of more than 85% in the groundwater mass flux of both tetrachloroethene and trichloroethene. Mass flux is the amount of contaminant moving with groundwater, so those figures do not mean groundwater flow fell by 85%. The authors also estimated an 86% reduction in total chlorinated volatile organic compound mass in that plot, while cautioning that movement of dense contaminant liquid during or after injection made the mass estimate uncertain.

The Parris Island work involved a different site and treatment formulation. Its figures cannot be transferred to Santa Susana or used as confirmation of DOE’s reported reductions there. It does show why longer observation matters: the older field test followed conditions for two and a half years, while DOE’s public account of the current pilot covers seven months of groundwater sampling through July 2026.

What comes next

DOE says it will keep sampling quarterly and use the data to inform future groundwater remediation in Area IV. Further measurements could show whether the initial reductions persist and how broadly they appear across the monitored area. For now, the public account leaves the size of the reported change and its durability unresolved. DOE has not given a date for selecting or completing a final groundwater remedy.