MTBE
Frequently Asked Questions
What is MTBE?
MTBE is a colorless chemical compound that is manufactured for use in
gasoline. It is a common component in reformulated fuels developed to
reduce smog and meet Clean Air Act requirements. MTBE has been used
in some gasoline as an octane booster since as early as 1979, but came
into statewide, year-round use in 1996.
The characteristics of MTBE are unlike those of other
gasoline constituents and solvents. MTBE is highly soluble and migrates
quickly with groundwater. It does not adhere well to soil particles,
and it does not appear to biodegrade significantly in the environment.
In March 1999, Gov. Gray Davis issued Executive Order
D-5-99 which concluded "...on balance, there is significant risk
to the environment from using MTBE in gasoline in California."
The executive order called for removal of MTBE from gasoline at the
earliest possible date, but not later than December 31, 2002.
In March 2002, the governor extended the phaseout of MTBE
by one year.
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How does MTBE get into our waters?
MTBE can get into groundwater from leaking underground fuel storage
tank systems and leaking petroleum pipelines. MTBE gets into surface
waters like lakes and reservoirs primarily from the use of motorized
watercraft. It may also travel into these waters in polluted runoff,
and small amounts may be deposited from the atmosphere by rainwater
or other means.
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How extensive is the occurrence of MTBE in Santa Clara County?
MTBE has been found at low concentrations in Coyote, Anderson and Calero
reservoirs. It has also been found in groundwater at more than 600 leaking
underground fuel storage tank sites investigated by the district's Leaking
Underground Storage Tank Oversight Program. The concentrations of
MTBE at these sites has ranged from 1 part per billion to several million
parts per billion. However, MTBE is mostly found in shallow groundwater,
groundwater that is very close to the ground surface. Most drinking
water supply wells tap groundwater that is hundreds of feet below the
surface and therefore are fairly well protected.
While very small amounts of MTBE (less than the reporting
levels) have been detected in at least one drinking water supply well
and some district treated drinking water, the concentrations are well
below those believed by the U.S. Environmental Protection Agency to
pose a health risk and below California’s drinking water standards.
The district is continuing to work with area water retail companies
to test all the public drinking water supply wells in the county for
MTBE and make sure customers receive water that is safe to drink and
tastes and smells good. Currently, MTBE is non-detectable in the county's
water supply.
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Why is MTBE a concern? Doesn't our drinking water get treated anyway?
In Santa Clara County, approximately half of our drinking water comes
from groundwater supplies. The other half is from local and imported
surface water supplies. Only the surface water is treated to remove
contamination. Research indicates that drinking water treatment technology
in place now does not remove MTBE from drinking water. To implement
a system that will remove MTBE from drinking water would be extremely
expensive. In Santa Monica, MTBE contamination led officials to shut
down half of the city's drinking water supply wells, leading to greater
dependence on more expensive imported water. It is the goal of the district
and the retail water companies to ensure that this does not happen in
Santa Clara County.
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What are the health effects of consuming MTBE?
There are little data on the human health effects of drinking MTBE contaminated
water, but it is a potential human carcinogen. The California Department
of Health Services, Office of Drinking Water has adopted a 5 parts per
billion drinking water standard that protects consumers from unpleasant
tastes and odors and a 13 part per billion drinking water standard that
protects consumers against health risks (See report).
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Will boating on water supply reservoirs be banned?
The water district board of directors considered banning gasoline-powered
watercraft from Anderson, Coyote and Calero reservoirs during the 1998
boating season to control levels of MTBE concentrations. However, the
board in concert with the Santa Clara County Parks and Recreation Department
adopted a compromise program for the 1998 boating season. The program
was revised in April 1999 to allow more flexibility, with the goal of
keeping MTBE concentrations in the reservoirs below 3 ppb. The revisions
include controlling the number of boats on the reservoirs and enforcing
the use of MTBE-free fuel.
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My drinking water comes from a private well. How can I tell if it has
MTBE in it?
MTBE has a distinctive, solvent-like odor that is detectable at relatively
low concentrations in the range of 10 to 130 parts per billion. The
actual range of detection may vary widely depending on an individual's
sense of smell and on the type and temperature of the source water.
The only definitive way to determine if there is MTBE in water is to
have it chemically analyzed. The district is investigating areas of
known MTBE contamination which may pose a threat to private water supply
wells.
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What is the district doing about MTBE?
The Santa Clara Valley Water District is concerned about protecting
the county's water supply, and is addressing MTBE on several fronts.
These include:
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