Remaining gasoline from a tanker rollover is transferred to another tanker. Wallagrass, Maine

Remaining gasoline from a tanker rollover is transferred
to another tanker. Wallagrass, Maine. May 2011

Wallagrass Gasoline Spill

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Remediation Update :: Frequently Asked Questions :: Contacts

On May 31, 2011 a tanker truck hauling 8,200 gallons of gasoline rolled over in the northbound lane of Route 11 in Wallagrass, Maine. In total, an estimated 5,000 gallons of gasoline was discharged into the soil and fractured bedrock below.

DEP is regularly monitoring possible contamination of nearby wells and as a precaution, has proactively placed temporary filters on several area homes near the spill site. The Department is also overseeing work of contractors performing cleanup and remediation activities.


Remediation Update

April 2, 2014

The Department will continue to collect samples from residential and groundwater monitoring wells in 2014. If the levels of gasoline continue to decrease as they have been, the Department anticipates approving the removal the piping and electrical hook ups for the treatment system and begin returning the site to pre-spill conditions by this fall.

In December 2012 the Department authorized the removal of gasoline recovery systems at the spill location due to the continued decrease of contamination in groundwater. These systems were removed in 2013; however as a precaution, the piping and electrical hook ups were left intact in order to easily re-install the gasoline recovery systems if contamination did not continue to decrease.

The Department has continued to collect samples from residential wells in the spill area on a quarterly basis to monitor the contamination. Samples were also obtained from groundwater wells installed specifically to monitor the contamination, as well as samples from nearby surface water locations. The results of groundwater and surface water monitoring have indicated that gasoline contamination concentrations continue to decrease in the groundwater, and many sampling locations no longer have gasoline detected or only at very low levels.



Gasoline in the ground exists in several phases and can leave the site by many pathways:

  1. There is liquid gasoline, the traditional oily liquid that you put in your car. Early on, Stantec recovered over 800 gallons of liquid gasoline. We do not anticipate further recovery of liquid gasoline from the site.

  2. There are components of gasoline that dissolve in water. For example, approximately 10% of the gasoline that spilled (i.e., 500 gallons) was composed of ethanol. Ethanol is regular drinking alcohol. Ethanol dissolves in water and also evaporates very quickly. The ethanol component of gasoline in the soil rapidly evaporates into the air and is consumed by soil bacteria. If any ethanol remains, the new soil vapor extraction system should remove it rapidly. Other components of gasoline are poorly-soluble in water, but will dissolve into water to some degree. These compounds include many of the more hazardous components of the gasoline, such as benzene. The new upgraded water treatment systems treat a very large quantity of ground water from the spill site in order to remove these dissolved-phase contaminants. Treating ground water to remove dissolved gasoline is not an efficient method of removing gasoline from the site but it protects the neighborhood from ground water contamination that might otherwise migrate from the spill zone into residential wells.

  3. There is vapor-phase gasoline in the air-filled pores and fractures in soil and rock at the spill site. This is a gasoline as a vapor or gas.

    The current remediation systems vacuum gasoline vapors out of the soil (“soil vapor extraction”) and effectively remove gasoline from the ground. As the existing vapor-phase gasoline is vacuumed from the pores and fractures in the soil and rock, the liquid-phase gasoline that is trapped and immobile in the soil (and thus not pump-able as a liquid) and dissolved-phase gasoline will evaporate and will provide even more gasoline vapor for the new soil vapor extraction system to recover.

    There is also evidence that the soil vapor extraction system is providing microorganisms in the soil with conditions that allow these microbes to digest gasoline.

Is my water safe to drink?
Private drinking water supply wells have been regularly sampled for contamination since the spill. As the Department gains more understanding of the concentration and distribution of contamination over time, it may change the sampling frequency and/or make decisions regarding which drinking water supplies are provided temporary treatment filters.

If water sampling results indicate that contaminant concentrations remain below health and safety guidelines and applicable drinking water standards for a sufficient amount of time to make a determination (typically a year), and evidence supports the conclusion that contamination is not expected to migrate to the well, the temporary treatment filters will be removed. Water quality sampling of untreated wells may continue as part of the overall site monitoring plan. The Department will not make the decision to remove temporary treatment filters lightly and will not put your health at risk. If the Department concludes that temporary treatment filters are no longer needed at your home, you should be confident that your drinking water supply is safe for you and your family. Even after the Department decides that filters are no longer needed, homeowners have the option of taking over the ownership, operation, and maintenance of the filters if they wish to continue using them.

If concentrations of contaminants remain above drinking water standards, the Department will seek to either replace your water supply with a new water supply that is not affected by the spill or install a long-term treatment system.
How long will the cleanup take?
The Department is unable to say with certainty how long it will take to completely clean up the site. Residents should understand that there will not be a recovery of all gasoline spilled as a substantial portion will volatilize into the air, dissolve into water, stick to rock and soil and/or be digested by microorganisms. The Department wants Wallagrass residents to be confident and comfortable in the fact that we will remain focused on ensuring the protection of their health and collaboratively with Stantec, other contractors and the responsible party, bringing this remedial action to a close in a way that is safest and most effective for the community and for the environment. We want the community to know we are working to ensure their continued safety and are grateful for the care and concern of the responsible party and related contractors.

DEP Contacts

Brian Beneski, Wallagrass Site Project Manager

Paul Higgins, Geologist

Nick Archer, Northern Maine Regional Director