VOCs: Volatile Organic Chemicals in
Private Drinking Water Wells
May 2009
What are VOCs?
Volatile Organic Chemicals (VOCs) are carbon-containing compounds
that evaporate easily from water into air at normal air temperatures.
(This is why the distinctive odor of gasoline and many solvents
can easily be detected.) VOCs are contained in a wide variety of
commercial, industrial and residential products including fuel oils,
gasoline, solvents, cleaners and degreasers, paints, inks, dyes,
refrigerants and pesticides.
People are most commonly exposed to VOCs through the air, in food,
through skin contact, and potentially in drinking water supplies.
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How do VOCs get into drinking water?
Most VOCs found in the environment result from human activity.
When VOCs are spilled or improperly disposed of, a portion will
evaporate, but some will soak into the ground. In soil, VOCs may
be carried deeper by rain, water or snow melt and eventually reach
the groundwater table. When VOCs migrate underground to nearby wells,
they can eventually end up in drinking water supplies.
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How extensively are VOCs found in drinking
water wells?
The U.S. Environmental Protection Agency (EPA) estimates that Volatile
Organic Chemicals are present in one-fifth of the nation's water
supplies. Minnesota Department of Health (MDH) studies suggest that
3 - 6% of public water supplies and about 2 - 4% of all water supplies
in Minnesota contain detectable amounts of VOCs.
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What factors contribute to VOC contamination
of well water?
Several factors increase the likelihood that a water supply will
be contaminated. One factor is the distance between the well and
a source of contamination. Many wells contaminated with VOCs are
located near industrial or commercial areas, gas stations, landfills
or railroad tracks.
A second factor is the amount of VOCs dumped or spilled. Some spills
are small and localized. Others occur over a long period of time,
or involve large quantities of contaminants. When a large quantity
of chemicals has leaked or spilled, as may occur with leaking underground
tanks or industrial spills, a large geographical area may be affected.
Third, the depth of a well can be a factor. Shallow wells are often
affected sooner and more severely than deep wells when contaminants
have been spilled on surface soils.
A fourth factor is local geology. Groundwater covered by thin,
porous soil or sand layers is most vulnerable. Dense, thickly layered
soils may slow down the movement of contaminants and may help to
absorb them.
The fifth factor affecting contamination of water is time. Groundwater
typically moves very slowly. A spill may take years to reach nearby
wells, so wells may not be contaminated until months or years after
the spill is discovered.
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What are the health risks associated with
VOC contamination?
VOCs vary considerably in their toxic (or harmful) effects. Researchers
have collected an extensive amount of information about the health
effects of VOCs, from animals studies, and from studies of human
exposures to large quantities of chemicals in the workplace.
Safe drinking water levels called health risk limits (HRLs) have
been established by MDH for many VOCs. HRLs are levels of chemicals
in drinking water that MDH considers to be safe for people to drink,
including sensitive people such as the very young or the elderly.
VOCs at levels higher than the HRLs may be harmful to the central
nervous system, the kidneys or the liver. VOCs may also cause irritation
when they contact the skin, or may irritate mucous membranes if
they are inhaled. Some VOCs are known or suspected carcinogens (or
cancer-causers).
For VOCs that do not cause cancer, conservative methods are used
to establish HRLs at levels considered safe, even if the water is
used every day for drinking, cooking, bathing, and laundry.
For carcinogens, HRLs are established so that drinking water with
levels above the HRL will cause no more than 1 additional cancer
for every 100,000 persons exposed over a lifetime of use, a very
small risk.
When more than one chemical is detected in a drinking water supply – even if levels are below the HRLs — additive effects
should be considered when deciding whether a water supply is safe
to drink. When compounds have similar effects, the HRLS for individual
chemicals may not be sufficiently protective.
Water containing chemicals at levels lower than the HRLs is considered
safe to drink. However, some individuals whose water has been found
to contain chemical contaminants at low levels may make a personal
choice to stop drinking their water or to investigate treatment
options.
Note: Interested parties may learn more about HRLs at the Health
Risk Limits for Groundwater and Toxicologic Endpoints table.
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What can be done about private wells that
are contaminated with VOCs?
Individuals who have received one report of the occurrence of VOCs
in their private well may wish to have the well retested before
taking action to treat or replace their water supply.
If chemical contamination is confirmed, construction of a safe,
uncontaminated well, or connection to a safe well or public water
system are the best options for private well owners whose water
contains VOCs at or above health risk limits.
When VOCs are detected at low levels, steps may be taken to prevent
further contamination by treating or removing the source. Removal
of the source is not always possible, and groundwater treatment
is costly and time consuming.
For some VOCs, temporary measures may include boiling the water
while venting the steam outside, using bottled water, connecting
to an uncontaminated neighboring well, or installing a home treatment
system.
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Home water treatment systems
Water treatment systems are available which can remove or reduce
VOCs. Some home filter systems - such as activated carbon filters
- can effectively remove VOCs if they are properly installed and
maintained.
Filtration systems may be installed for point-of-use treatment at
the faucet, or point-of-entry treatment where water enters the home.
Point-of-entry systems are preferred for VOCs because they provide
safe water for bathing and laundry, as well as for cooking and drinking.
It is important to determine exactly which contaminants are present
in water before choosing a system. Then, treatment systems should
be checked periodically to ensure that they are operating properly.
When should a private well be tested for VOCs?
Testing of private well water for VOCs and petroleum products
is indicated if the water has the taste or odor of gasoline or solvents.
Wells should also be tested if they are within one to two city blocks
(500 to 1000 feet) of a former or existing gasoline service station,
or other fuel tanks.
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What can Minnesota residents do about the
VOC problem?
Individuals can help to prevent future contamination by restricting
use of toxic chemicals and by disposing of them properly. Underground
fuel tanks should be regularly checked for leaks and removed when
they are no longer secure. Spills and leaks should be reported immediately
to the Minnesota
Duty Officer at 1-800-422-0798.
Who can I contact to have my well water
tested?
For a list of all laboratories certified by Minnesota to test
drinking water for VOCs see Certified Environmental Laboratories.
For further information
If you have questions about your water supply or would like more
information, contact one of our offices and ask to speak with a
well specialist. Go to Contacting
the Well Management Section.
Printable information sheet (PDF: 53KB/3 pages)
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For more information about this page, please contact us at health.hazard@state.mn.us call 651-201-4897, or toll-free 1-800-657-3908 and press "4" to leave a message.
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