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A Confluence of Factors
Creating
the Situation
In piecing together the
events that took place in Pascoag in the fall of 2001, it quickly
becomes apparent that numerous factors combined to create
a situation that most officials interviewed described as unprecedented.
Engineers at DEM, HEALTH and the PUD agreed that the nature of the
Pascoag contamination was exceptional not only in the relatively
large distance the contaminant traveled from the source of the
gasoline release, but also in the speed with which contaminant
levels rose in the water supply. Several factors contributed to
the severity of the contamination:
- The chemical nature
of MTBE. Methyl tertiary-butyl ether, added to gasoline in
significant quantities beginning in 1992 following amendments
to the US Clean Air Act of 1990, is highly water-soluble. When
a gasoline release occurs, MTBE often moves significantly farther
and faster than the other chemical constituents of gasoline.
- Topography and
geology. Engineers at the PUD and DEM noted the downhill gradient
from the Mobil station to the wells as a contributing factor in
the contamination. Some also suggested that fractures in the bedrock
that predominates in the region of the wells may have provided
a conduit for the contaminant to move rapidly. The high-yield
Pascoag wells, pulling upwards of 500 gallons of water per minute,
may also have contributed by drawing the contaminant toward the
groundwater aquifer.
- Lack of redundancy
of wellsource. Although the Pascoag Utility District had installed
a second well in February of 2001, this well was housed in the
same building as the first well and located just ten feet away.
According to PUD General Manager Ted Garille, the district believed
that the wells, though very close together, drew from separate
aquifers. Nonetheless, both wells were found in September to be
pumping MTBE-contaminated water.
- Underground Storage
Tank facility within the Wellhead Protection Area (WPA). The
Wellhead Protection Area Program, required by the US EPA and administered
in Rhode Island by the Department of Environmental Management,
prohibits the installation of new underground storage tank facilities
within a designated area surrounding a wellsource. This area is
determined by a formula that incorporates well capacity, local
geology and other factors. The Main Street Mobil Station pre-existed
the WPA rules and lies within the Pascaog wellhead protection
area, approximately 1700 feet from the wells.
What
about the rest of Rhode Island?
Although the Pascoag
contamination was unparalleled in the experience of DEM and HEALTH
officials, this should not be taken to imply that the contamination
faced by Pascoag was an improbable event. Many of the same factors
that devastated Pascoag's public water supply exist in dozens of
other towns and villages across Rhode Island. These include, but
are not limited to:
- A large number
of small public water supplies with limited financial resources
- Non-compliant
underground storage tank owners
- Underground storage
tanks in close proximity to water sources
According to statistics
from HEALTH, as of July 2002 there were 389,858 Rhode Island
residents served by water systems with known underground storage
tanks located within half a mile of the well. Most of the state
and local officials interviewed believe there to be a high probability
that another similar contamination event will occur in Rhode
Island; some described such an event as inevitable. According to
Janis Loiselle, senior policy advisor to Governor Almond, the next
contamination in Rhode Island is not a question of "if"
but of "when".
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