Outline

Background
    What is Trichloroethylene?
    Uses of Trichloroethylene
    Chemical and Physical Properties of Trichloroethylene
    Exposure to Trichloroethylene
    Health Effects of Trichloroethylene
    Regulatory Status of Trichloroethylene
    Environmental Factors of Trichloroethylene

Goals of Investigation

Investigation
    Data Retrieval and Modification
    GIS Maps
    Data Incorporation with GIS Maps
    TCE Value Illustration
    Water Usage Illustration
    EPA Limit Illustration

Conclusions

References

Report

Background

What is Trichloroethylene?

    Trichloroethylene (TCE) is a colorless, nonflammable liquid that has a sweet odor and a sweet, burning taste (ATSDR, 1997).  Its odor has been likened to that of ether and chloroform.  TCE is also known by the names Triclene, Vitran, and Chlorilen among several others.

Uses of Trichloroethylene

    For the most part, TCE is used in industrial settings as a solvent to remove greases, oils, waxes, and tars from metal parts in machinery.  Vapor degreasing of these metal parts accounts for eighty percent of trichloroethylene’s use (EPA, 2001).  Some types of industries that use TCE include electroplating, integrated iron and steel manufacturing, machinery manufacturing and repair, metal degreasing, pulp and paper manufacturing, and rubber manufacturing (ED, 2001).  TCE can also be found as an ingredient in various consumer products.  These products include laundry spot removers, general performance sealants, lubricating oils, automotive chemicals, paint and varnish removers, sheet vinyl flooring, synthetic resin and rubber adhesives, and typewriter correction fluid (ED, 2001).  In the past, trichloroethylene was used as a general anesthetic.

Chemical and Physical Properties of Trichloroethylene

    The chemical formula for TCE is C2HCl3 and its CAS identification number is 79-01-6.  TCE has a density greater than water at a value of 1.465g/cm³, will boil at 87C, and will freeze at –73C (EPA, 2001).  It has very high mobility in soils, which is one of the reasons it is an important chemical to remove from contaminated environments.  TCE is soluble in water with a value of 1g/L (EPA, 2001).

Exposure to Trichloroethylene

    TCE can be found in air, soils, and groundwater sources.  Humans can also be exposed to TCE by using the industrial cleaning solvents mentioned above.  TCE enters the human body by breathing contaminated air, drinking contaminated water, or by direct contact with skin.  When the chemical enters via breathing, the body accepts about half of the content into blood and organs while the rest is exhaled (ATSDR, 1997).  Drinking will put the chemical into the blood.  Contact with the skin can put some chemical into the body, but not nearly as much as breathing and drinking.  Once in the bloodstream, the liver breaks most of the TCE down into other chemicals, which are passed safely through the body within a day (ATSDR, 1997).  Much of the chemical will leave the bloodstream via exhalation, as well.  Some TCE or its broken down components can become trapped in fat cells temporarily and may build up if exposure is long-term (ATSDR, 1997).

Health Effects of Trichloroethylene

    Exposure to TCE produces both serious and non-serious health effects.  Acute (short-term) as well as chronic (long-term) inhalation exposure to low levels (<100ppm) of TCE generally results in effects to the central nervous system with symptoms including dizziness, headaches, facial numbness, euphoria, nausea, confusion, and blurred vision (TTN, 2001).  These symptoms have been noted when TCE is at levels where it can be detected by odor in the air.  Effects to the gastrointestinal system, liver, kidneys, and skin have also been reported with low levels of TCE exposure.  Acute exposure to extremely high TCE levels (>10,000ppm) has been known to cause death in humans via cardiac arrhythmias or massive liver damage (TTN, 2001).  In animal testing, enlarged livers occurred with exposure to moderate levels of TCE while liver and kidney damage occurred at high levels of TCE exposure (ATSDR, 1997).

    Though TCE is not yet considered a carcinogen to humans, it has been shown that high doses of TCE can cause cancer in animals.  TCE has been nominated to be listed in the National Toxicology Program’s 9th Report on Carcinogens (ATSDR, 1997).  The committee responsible for this report has been evaluating TCE continuously since its nomination.  The Environmental Protection Agency (EPA) is currently re-evaluating TCE but has previously labeled it as an intermediate between a probable and possible human carcinogen (TTN, 2001).

Regulatory Status of Trichloroethylene

    In 1989, the EPA set a TCE level of 5ppb for all drinking water sources that serve more than 25 people for a period of more than six months (ATSDR, 1997).  The EPA also requires spills of more than 1,000 pounds of TCE to be reported (ATSDR, 1997).  A proposal has been made to reduce this value to 100 pounds.  The Occupational Safety and Health Administration (OSHA) has also set regulations on TCE.  A TCE concentration of 100ppm in the air is the occupational exposure limit for 8-hour days in a normal 40-hour workweek (ATSDR, 1997).  OSHA also allows 15-minute exposure to be less than 300ppm (ATSDR, 1997).

Environmental Factors of Trichloroethylene

    The release of TCE into the environment is mainly due to air emissions from degreasing plants.  TCE may be released directly into water sources via wastewater from metal finishing, paint and ink formulation, and rubber processing industries (EPA, 2001).  According to the Toxics Release Inventory (EPA, 2001), over 100,000 pounds of TCE was released to water sources from 1987 to 1993.  Pennsylvania and Illinois top the list of states with the highest reported total environmental releases of TCE (ED, 2001).  Pennsylvania also tops the list of states with reported water releases of TCE.  Fabricated metal production is the industrial sector with the highest reported total environmental releases as well as the highest reported water releases (ED, 2001).

    When TCE is released into the environment, it generally evaporates and breaks down relatively quickly (ATSDR, 1997).  The breakdown occurs much slower in groundwater, however, because of low evaporation rates.  TCE fails to break down in soils and because of its mobility in soils, it finds its way to groundwater sources easily.

Goals of Investigation

    Since TCE is hazardous to human health, I wanted to examine the extent of TCE contamination in groundwater sources across the United States.  GIS will be used to graphically illustrate the values of TCE in groundwater as well as the uses of those water sources, focusing on those sources used for drinking water.  Also I will take a closer look at TCE contamination in my home state of California.

Investigation

Data Retrieval and Modification

    The first step in this investigation was to retrieve a dataset with TCE values in groundwater across the United States.  I found this by visiting the United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) Program website.  The file was downloaded and manipulated as an Excel workbook.  The original dataset included state names, county names, source (groundwater), water usage, land usage, well depth, sampling date, and values of TCE concentrations measured in micrograms per liter.  For this investigation, land usage, well depth, and sampling date were not needed.  The modified dataset with the information used for this investigation can be viewed by clicking here.  Figure 1 shows a truncated sample of the data table.

GIS Maps

    The next step for this project was to find a map of the United States.  I navigated to the D:/ drive of the computers here in the USU Geomatics Computer Lab.  There I located the USA County map in the ESRI folder.  In order to be able to manipulate and change the data in the map files, the files were copied onto my personal I:/ drive.

Data Incorporation with GIS Maps

    Now that I had both the TCE data and the USA County map at my fingertips, I needed to find a way to incorporate the data that each contained in a logical and illustrative way.  The simplest method turned out to be adding two fields to the attribute table of the USA County map file.  The two fields added were "TCE" to contain the measured values, and "Water_Usag" to contain the description of human usage for each of the contaminated sources and are shown in Figure 2.

    The TCE data file was manipulated in Excel.  Because there were often several well readings for each individual county, an average TCE value was calculated for incorporation with the USA County map.  The most common use noted for the groundwater sources in each county was added in the next column.  After these two columns had been completed in the Excel TCE data file, the USA County map attribute table was opened in Excel.  The data on average TCE value and most common usage was entered into the corresponding counties listed in the attribute table.  Figure 3 shows a portion of the attribute table following this important addition of data.

TCE Value Illustration

    After the average TCE values and most common usages were incorporated into the attribute table, the project was ready for the next phase of using the attributes to illustrate contamination in the United States.  The modified USA County map was opened using ArcMap.  The first analysis consisted of assigning a graduated color scheme to the values of TCE.  This was accomplished by right-clicking on the map title and selecting Properties.  In the Symbology tab within Properties, the options for Quantities and Graduated Colors were selected and the field was specified to be TCE.  This same process was conducted for the TCE Value illustration of the state of California.  Figures 4 and 5 show the maps of the United States and California, respectively.

Water Usage Illustration

    Now that the values of TCE found in the groundwater were plotted on the map, the file was saved and a new data frame was added.  The USA County map file used for the TCE Value illustration was added to this new data frame.  Under Properties, the option for Categories Unique Values was chosen in the Symbology tab.  The field was selected to be Water_Usag and all values were added.  The colors for domestic and public supplies were changed from the computer chosen shades to be orange and red in order to stand out vibrantly on the map.  These colors were also chosen because they tend to symbolize danger or caution, both of which may be applicable to TCE contaminated groundwater sources.  Again, the same process for Symbology was followed to illustrate the distribution of groundwater sources in California.  Below the two maps are shown as Figures 6 and 7.

EPA Limit Illustration

    As stated above, the Environmental Protection Agency (EPA) has set a limit of 5ppb in drinking water that serves more than 25 people for a period of more than six months.  Since almost all of the TCE contaminated groundwater sources are shown to be domestic or public supplies, the next step was to determine how many of these were at levels of TCE above the EPA standard.  This procedure was much the same as creating the graduated color scheme on the first two maps shown in Figures 4 and 5.  Instead of having the color scheme gradually get brighter in color with higher values of TCE, the two highest value ranges were given dark colors while the lower value ranges were given light colors to differentiate between the two.  As illustrated in Figures 8 and 9 below, there are a few groundwater sources above 5ppb marked in red on the map of the United States.  There are numerous sources across the United States and in California that are between 0.1ppb and 4.8ppb.  These sites need to also be considered as potentially harmful groundwater sources, especially if they continue to be fed with more TCE contamination.

Conclusions

    As illustrated by the maps produced in ArcMap, there is widespread contamination of groundwater sources in the United States by trichloroethylene (TCE).  Most of the sources have TCE values of less than the Environmental Protection Agency's Drinking Water Standard of 5ppb.  There are some hotspots, however, that demand attention and remediation.  Almost all of the groundwater sources that are used for human purpose are used for domestic or public drinking water supply.  This is a major concern because even with TCE contamination values less that 5ppb, it is possible that humans are being exposed to the harmful effects of TCE.  These sources, especially those between 0.1ppb and 4.8ppb, need to be examined and possibly cleaned up as well.

    Upon a closer look at my home state of California, there is some TCE contamination in the 0.1ppb to 4.8ppb range that should be studied and potentially remediated.  All of these sites with this TCE value range are domestic or public supply groundwater sources, which is further evidence that these sites need attention.

    A source of error in this investigation stems from the original dataset downloaded from the USGS NAWQA website.  This dataset included no TCE information for the site where my thesis project is centered, Hill Air Force Base in Ogden, Utah.  One reason for this may be that Hill AFB is a government site and perhaps the file included data from only private sites.  Something to look at in more detail in the future is a dataset including all government sites in the United States and to compare the TCE values in the government and private sectors.

    Overall, GIS has proven to be a useful tool in my study of TCE in groundwater.  As a future hydrogeologist, I plan to use GIS in similar ways as I continue to examine groundwater and soils contamination in my career.

References

Agency for Toxic Substances and Disease Registry (ATSDR), Public Health Statement for Trichloroethylene, 1997
http://www.atsdr.cdc.gov/ToxProfiles/phs8824.html

Environmental Defense (ED) Scorecard, Chemical Profile for Trichloroethylene, 2001
http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=79-01-6

Environmental Protection Agency (EPA) Office of Water, Technical Fact Sheet on Trichloroethylene, 2001
http://www.epa.gov/OGWDW/dwh/t-voc/trichlor.html

Technology Transfer Network (TTN) Web Unified Air Toxics Website, Trichloroethylene Fact Sheet, 2001
http://www.epa.gov/ttn/uatw/hlthef/tri-ethy.html