04/08/2026
Dry Cleaners & How Solvent Contaminants Break Down
Dry cleaning operations have historically used chlorinated solvents such as tetrachloroethylene (PCE)—a persistent compound that can impact soil and groundwater. These compounds are classified as dense non-aqueous phase liquids (DNAPLs), meaning they are heavier than water and can migrate downward through the subsurface, accumulating at depth and acting as long-term contaminant sources.
Once released, PCE doesn’t simply disappear. Instead, it undergoes a stepwise breakdown process in the subsurface:
PCE (tetrachloroethylene) → TCE (trichloroethylene) → DCE (dichloroethylene) → VC (vinyl chloride) → ethene
This process, known as reductive dechlorination, typically occurs under anaerobic (low oxygen) conditions and is driven by naturally occurring microorganisms.
Why this matters:
• Breakdown products can be more mobile and, in some cases, more harmful to potential receptors (e.g., vinyl chloride)
• DNAPL behaviour can lead to persistent source zones and complex plume distribution
• Plumes can evolve over time, requiring ongoing monitoring and adaptive site models
• Understanding degradation pathways is critical for risk assessment and remediation design
Effective site characterization goes beyond identifying PCE—it requires evaluating the full suite of daughter products and subsurface conditions influencing degradation and contaminate fate.
