Background on PCE
What is PCE?
Tetrachloroethene (pronounced tet'ra klor'o eth-een), or PCE, is a manufactured chlorinated organic compound that can be used as an intermediate product in chemical manufacturing and as a solvent by automotive repair shops, paint shops, machine shops, service stations and dry cleaning establishments. It is also used in some consumer products. PCE is also commonly referred to as tetrachloroethylene, perchloroethylene and PERC. At room temperature, PCE is a nonflammable liquid, and its extensive use from the 1940s through the 1980s had much to do with it being much safer than the flammable solvents used previously. PCE use has decreased since the 1980s because of increased efficiencies in the industrial processes where PCE is used, concerns over environmental impacts, and availability of alternative solvents. Currently, dry cleaning businesses and chemical manufacturers are the primary users of PCE.
What are the physical characteristics of PCE?
Liquid PCE is denser than water, and has a limited tendency to mix with or dissolve in water. In fact, only about 1.5 fluid ounces of PCE will dissolve in 100 gallons of water. Any additional PCE added to 100 gallons of water would exist as a separate liquid phase, much like what happens when water and oil are mixed. As a result of its low solubility and high density, liquid PCE tends to "sink" through water and can exist in the groundwater environment as a separate dense non-aqueous phase liquid (or DNAPL) that will collect or pool at or along low points.
PCE has a high vapor pressure allowing it to easily evaporate into the air. This characteristic of PCE contributes to our being able to remove PCE from groundwater during remediation by air stripping.
PCE has a sharp, sweet odor. Most people can smell PCE when it is present in the air at a level of 1,000 parts PCE per billion parts of air (1,000 ppb); however, some people have a more sensitive sense of smell and can detect it at even lower levels.
What happens to PCE in the environment?
Given the high vapor pressure of PCE, much of it that enters into the environment evaporates into the air, where it can then be broken down by sunlight or brought back to the land surface by rain.
Small amounts of PCE (roughly 0.012 % by volume) can dissolve in surface water or groundwater. This PCE will move as a dissolved phase along with the water. However, larger amounts of PCE can exist as a separate DNAPL. This DNAPL will tend to move vertically downward and collect in low spots or along impermeable barriers. DNAPL is difficult to detect in the environment and can act as a source for dissolved PCE in groundwater over time.
Under certain conditions in soil and/or groundwater, naturally occurring microorganisms can break PCE down through a process known as reductive dechlorination. Under oxygenated conditions in soil and/or groundwater, PCE tends to be environmentally persistent. In the central Truckee Meadows the groundwater system is oxygenated and the conditions conducive to the natural breakdown of PCE are generally absent.
Underground Movement of PCE
How might I be exposed to PCE?
When you pick-up clothes at the dry cleaners, small amounts of PCE can be released into the air. These PCE vapors can be inhaled. Also, if you use solvents or degreasing agents at work or in your hobbies these products may contain PCE. Use of these products can release PCE vapors into the air, which can then be inhaled.
In addition, PCE originating from product spills or contaminated sites can be exposed in excavations. People working in these excavations can be exposed to PCE present as a liquid through skin contact or vapor through inhalation. PCE originating from product spills or contaminated sites can also infiltrate nearby buildings as a vapor. People living or working in these buildings can potentially be exposed to PCE through inhalation.
Finally, PCE could be ingested as a result of drinking water containing PCE. The activities of the CTMRD program are intended to ensure that municipal water supplies in the central Truckee Meadows provide safe drinking water.
Can PCE affect my health?
The U.S. Environmental Protection Agency (EPA) considers PCE in drinking water a potential risk to human health. The EPA has defined the maximum contaminant level (MCL) for PCE as 5 micrograms per liter (μg/L). The EPA indicates that potential effects to long-term exposure above this level could include liver problems and an increased risk of getting cancer. It only takes a small amount of PCE to contaminate water to concentrations above the MCL. Approximately 1 teaspoon of PCE would contaminate 450,000 gallons of water to a dissolved PCE concentration exceeding the MCL.
Additionally, exposure to high concentrations of PCE vapors (as might occur in closed, poorly ventilated areas) can cause dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and (in extreme cases) death.
How did PCE come to be a problem in the central Truckee Meadows?
As indicated previously, PCE was used extensively from the 1940s into the 1980s. During this timeframe, regulations governing PCE use and disposal were initially non-existent and early regulations (enacted in the late 70s) were less strict than they are today. As a result, unregulated or poorly regulated PCE use and disposal practices resulted in releases to the environment, and ultimately to contamination of the Truckee Meadows aquifer system. During initial investigations into the presence of PCE in the central Truckee Meadows, information was gathered to evaluate potential historic sources (1940-1991). Three hundred and twenty potential sources (including businesses such as dry cleaners, automobile repair and paint shops, and gasoline service stations) were identified in the greater Downtown Reno area alone. Due to the large number of potential sources, correlating the PCE in groundwater in the Truckee Meadows to a specific source was not possible.
The majority of PCE contamination in the central Truckee Meadows aquifer system has come from historical sources; that recognition is why the CTMRD program was created to manage the problem. However, in the event that a recent or ongoing illicit release is discovered that can be attributed to a specific source, it will be referred to and handled by the Nevada Division of Environmental Protection (NDEP). Currently, there are seven PCE-related corrective actions in the central Truckee Meadows that are being administered by NDEP.
Find out what the CTMRD program and other agencies are doing to address the PCE problem in the central Truckee Meadows.