PCE contamination occurs when tetrachloroethylene, a widely used industrial solvent, enters soil, groundwater, or indoor air. PCE (also called perchloroethylene or “perc”) has the chemical formula C2Cl4 and is primarily used in dry cleaning and metal degreasing. It’s one of the most common groundwater contaminants in the United States, and it poses serious health risks because it persists underground for decades and can migrate long distances from where it was originally released.
Where PCE Contamination Comes From
The two biggest sources of PCE contamination are dry-cleaning operations and metal degreasing facilities. For decades, these industries used PCE as a go-to solvent because it dissolves grease and oils without damaging fabrics or metal parts. The problem is that PCE routinely leaked into the environment through spills, improper disposal, faulty storage, and wastewater discharge. Chemical production facilities that manufacture or process PCE are another source.
Many contamination sites trace back to practices from the 1950s through the 1980s, when environmental regulations were minimal. At one well-documented site in South Carolina, roughly 1.7 million kilograms of chlorinated solvents (primarily PCE) were released into the ground over about 35 years through a settling basin and leaking sewer lines. That kind of large-scale release was not unusual for the era, and the contamination it created is still being managed today.
How PCE Behaves Underground
PCE is heavier than water. When it seeps into the ground, it sinks through the soil and can plunge deep into underground aquifers as what environmental scientists call a “dense non-aqueous phase liquid,” or DNAPL. Instead of floating on the water table like oil, PCE pools at the bottom of aquifers and slowly dissolves into the surrounding groundwater over time. This creates contamination plumes that can stretch for kilometers.
What makes PCE especially difficult to deal with is its persistence. The pooled solvent acts as a long-term source of contamination, continuously dissolving into flowing groundwater. Research has confirmed that PCE can migrate as a dense liquid more than 650 meters from where it was originally released, far beyond what many site assessments initially assumed. The contaminated groundwater plumes extending from these sources can be even longer. This is why PCE contamination discovered decades ago at former industrial sites continues to affect drinking water wells and neighborhoods today.
How PCE Reaches People
There are three main ways people come into contact with PCE from a contaminated site.
The first is drinking water. PCE dissolves into groundwater, which feeds wells and municipal water supplies. The EPA has set the maximum contaminant level for PCE in drinking water at 0.005 milligrams per liter (5 parts per billion), with a health goal of zero. Any detection in drinking water is considered a concern.
The second is vapor intrusion. PCE evaporates easily, and contaminated soil or groundwater can release chemical vapors that travel upward through the ground. These vapors enter homes and businesses through sump pumps, floor drains, and cracks in basement floors or foundations. You can be exposed to PCE in your indoor air without ever knowing there’s contaminated groundwater beneath your building. This pathway is a particular concern for people who live or work near current or former dry-cleaning shops.
The third is direct contact with contaminated soil, though this is less common for people outside of workers at active cleanup sites.
Health Risks of PCE Exposure
PCE primarily affects the brain and nervous system, the liver, and the kidneys. The International Agency for Research on Cancer classifies it as a Group 2A carcinogen, meaning it is “probably carcinogenic to humans.” The U.S. National Toxicology Program similarly classifies it as “reasonably anticipated to be a human carcinogen.”
Chronic, lower-level exposure causes subtler but well-documented neurological effects. Studies of dry-cleaning workers and people living in buildings near dry cleaners have found three consistent patterns of harm: impaired color vision, reduced visuospatial memory, and slower reaction times. Dry-cleaning workers exposed to PCE showed measurably worse color vision compared to unexposed people, and their scores deteriorated further as exposure continued over time. In one follow-up study, workers exposed to increasing PCE concentrations experienced an additional 6% decline in color vision scores over just two years.
Memory and cognitive effects appear even at relatively low concentrations. In one residential study, people with an average exposure of just 0.7 parts per million of PCE scored 15% lower on visual memory and cognitive function tests compared to unexposed individuals. Occupational studies found cognition error rates ranging from 4 to 30% at exposures between 12 and 23 ppm, depending on the type of cognitive task. Reaction times were 10 to 20% slower in both occupational and residential settings. These are not dramatic, obvious symptoms. They’re the kind of gradual cognitive changes that can go unnoticed for years.
How PCE Contamination Is Cleaned Up
Cleaning up PCE is expensive and slow, in part because the chemical sinks so deep and persists so long. Remediation typically targets both soil and groundwater separately.
For contaminated soil, the most common approaches are excavation and removal (physically digging out the contaminated dirt), soil vapor extraction (applying suction to underground wells to pull PCE vapors out of the soil), and bioventing, which encourages naturally occurring bacteria to break down the solvent by increasing airflow through the soil.
Groundwater cleanup is more complex. Pump-and-treat systems pull contaminated water to the surface for treatment, but this can take decades for large plumes. Bioremediation involves injecting compounds underground that help bacteria break down PCE into less harmful chemicals. Chemical oxidation destroys PCE by injecting reactive chemicals directly into the contaminated zone. Permeable reactive barriers are walls of reactive material installed underground in the path of a contamination plume, treating the water as it flows through. Air sparging pushes air into groundwater to strip out the dissolved PCE, which is then captured by vapor extraction at the surface.
No single method works for every site, and many cleanups use a combination of these technologies. Timelines for full remediation often span years to decades, particularly at sites where PCE has pooled as a dense liquid deep in an aquifer.
What PCE Contamination Means for Your Property
If you live near a current or former dry cleaner, metal degreasing facility, or industrial site, PCE contamination could affect your groundwater or indoor air. State environmental agencies maintain databases of known contamination sites, and many require active monitoring and notification of nearby residents. If your home uses a private well rather than a municipal water supply, testing for PCE is especially important since municipal systems are required to monitor for it, but private wells are not.
Vapor intrusion can be assessed by testing indoor air or placing monitors beneath a building’s foundation. If PCE vapors are detected, mitigation systems similar to radon ventilation systems can be installed to redirect vapors away from living spaces. These systems use fans and sealed piping to pull vapors from beneath the foundation and vent them safely above the roofline.