fundamental rule of ecology states that we can never simply do just
one thing; that, in effect, everything is connected to everything
else. Like a pebble dropped into a pond, consequences
both intended and unintended ripple outward from all that we
this, most of us do our best to minimize the negative consequences
of our actions and maximize the benefits for ourselves and
for others. In dealing with hazardous waste and toxic substances,
we do our best to practice prevention and reduce the use of toxics
in order to avoid generating waste in the first place. Because were
not always successful, however, considerable effort is necessary to
control waste and emissions, and to clean up the environment after
a spill or other release. Because we can never do just one thing and
because we can never know all the many consequences of what we do
before we do it, sometimes our best decisions about environmental
protection create new, unforeseen problems. An example worth considering
involves attempts to reduce vehicle-related air emissions.
like the rest of the United States, is highly dependent on motor vehicles
for transportation. The automobile has afforded us great mobility,
but at a price. Gasoline, as well as emissions resulting from the
use of gasoline, are among the most prevalent hazardous substances
to which we Vermonters are exposed in our everyday lives.
the phase-out of lead from gasoline in the late 1970s (which dramatically
reduced lead in the environment), compounds that contain oxygen, called
oxygenates, have been added to gasoline to increase its combustibility.
This use of oxygenates was expanded by the Clean
Air Act Amendments of 1990, which mandated that oxygen be added to
gasoline in areas where concentrations of ozone in the summer or carbon
monoxide in the winter exceed established air quality standards. Vermont
monitors ground-level ozone at two stations, Bennington and Underhill.
Annual ground-level ozone averages consistently hover at or just below
the national ambient air quality standard (Figure 1).
in the upper atmosphere helps filter cancer-causing ultraviolet radiation,
but ozone near the ground damages lungs and possibly the human immune
system. In the lower atmosphere, hydrocarbons and nitrogen oxides
reacting in sunlight and heat form ozone. Some ground-level ozone
in Vermont is formed from the nitrogen oxides blown in from midwestern,
coal-burning power plants.
tertiary-butyl ether (MTBE) is a volatile organic compound derived
from natural gas. It is added to gasoline either seasonally or year-round
in many parts of the United States to increase the octane level and
to reduce carbon monoxide and ozone levels in the air.
all gasoline sold in Vermont contains MTBE. As in other New England
states, it is found at a concentration of approximately 5 to 10 percent,
but may be present in higher concentrations because the same gasoline
is distributed in states that require higher levels of oxygenates
such as MTBE.
has entered groundwater and surface waters in Vermont through leaking
underground gasoline storage tanks, spills, emissions from marine
engines into lakes and reservoirs, and to some extent from air deposition.
Once released into the environment, MTBE behaves differently from
other gasoline compounds. MTBE does not adhere to soil particles and,
because it is more soluble in water than other components of gasoline,
it migrates farther and more quickly with groundwater and surface
waters. In addition, MTBE resists being rendered harmless by soil
and aquatic organisms (biodegradation).
U.S. Environmental Protection Agency tentatively classifies MTBE as
a possible human carcinogen. Vermonts ground water rules recommend
a limit of 40 parts per billion (ppb). This recommendation is based
on preventing taste and odor complaints. MTBE has a very low odor
threshold at 20 ppb, while the threshold for taste is 40 ppb. These
numbers vary widely with individual sensitivity. The Vermont Agency
of Natural Resources has adopted a health advisory of 40 ppb for MTBE.
Water samples at or exceeding this concentration trigger the need
for remediation. To date, more than 175 private
and 44 public drinking water wells have been contaminated to some
level by petroleum products many of these solely by MTBE.
number of sites contaminated by petroleum has increased steadily since
the late 1980s but seems to be stabilizing due to investments in double-walled
underground storage tanks (Figure 2). The Agency monitors nearly 1,200
sites contaminated by petroleum; of these, an estimated 85 percent
1997, northeastern states and responsible parties spent about $168
million dollars to clean up gasoline spills, primarily from leaking
underground storage tanks. A precise apportionment of the costs related
to MTBE contamination, however, is not available because Vermont and
the other states do not compile data on specific gasoline constituents.
of waters contaminated with MTBE is particularly difficult because
of its chemical properties. MTBE can spread rapidly over large areas
and is very resistant to biodegradation. Consider, for example, an
underground storage tank leak that occurred in Killington, a release
site surrounded by vacation homes, restaurants, retail shops, and
two apartment complexes. Within a 2,000-foot radius of the leaking
tank are more than 80 bedrock drinking water supply wells. As the
gasoline leaked from the tank, a plume of MTBE and other compounds
found in gasoline spread through the bedrock aquifer and ultimately
contaminated 27 water supply wells. Twenty-five of these wells were
contaminated solely by MTBE, two by other gasoline compounds. The
MTBE migrated nearly 10 times the distance of the non-MTBE gasoline
contaminants. Today, six years after the leak was stopped, most of
the non-MTBE gasoline contaminants have been recovered, but much of
the MTBE remains, beyond the reach of even the most sophisticated
contamination caused by MTBE has raised new questions about the desirability
of this additive. The Agency, in partnership with other New England
states, is working to better understand its risks and benefits.