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Division of Spill Prevention and Response


Updated: Oct. 24, 2017

Project History: Technical Activity and Public Outreach

Table of Contents


1970 - 2008


    photo of North Pole Refinery

    View more information on the site history of the North Pole Refinery in DEC's Database of Contaminated Sites.

  • 1977 - Refinery begins production using crude oil from the Trans-Alaska Pipeline.
  • 1970s to early 1980s - Petroleum product leaks from above-ground storage tanks, consequently these tanks are taken out of service.
  • 1980 - MAPCO purchases the refinery.
  • 1985 – Sulfolane unit installed.
  • 1986 - DEC issues a Compliance Order by Consent, which outlines a cleanup and monitoring strategy for the petroleum contamination.
  • Mid - late 1980s - Monitoring well data indicates that groundwater on the refinery Is contaminated with petroleum compounds, such as benzene, ethylbenzene, toluene, xylenes, (BTEX) trimethylbenzenes and naphthalene above DEC’s regulatory maximum contaminant levels for drinking water. The drinking water used at the refinery is tested and found to be unaffected, as is the city water system. At this time, the refinery begins treatment and monitoring of the groundwater and performs further site characterization.
  • 1989 - The US Environmental Protection Agency (EPA) issues two Resource Conservation and Recovery Act (RCRA) Administrative Orders to MAPCO. The orders outline a cleanup and monitoring strategy for the RCRA hazardous waste violations.
  • 1998 - MAPCO merges with The Williams Companies.
  • 2004 - The Williams Companies sells the facility to Flint Hills Resources.


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  • 2009 Outreach

    • November 20: A comprehensive DEC website on the sulfolane investigation is established.
    • November 23: DEC holds its initial public meeting in North Pole. Representatives from DEC, Flint Hills Resources and DHSS participate.

    October-November - Sulfolane is discovered in wells north of the refinery property boundaries: Flint Hills (FHR) begins testing groundwater in monitoring wells outside of its property, near private homes with drinking water wells. Sulfolane concentrations in the monitoring wells are higher than expected, although below the 350 micrograms per liter cleanup level previously established for onsite wells.
    • Flint Hills, as the responsible party, notifies DEC with the results and with a plan to immediately supply alternate water and begin testing residential wells. Bottled water is provided to those impacted.
    • DEC asks the Alaska Department of Health and Social Services (DHSS) for assistance in reviewing the sulfolane cleanup level for its protectiveness of human health.



View more detailed information on the site history of the North Pole Refinery in DEC's Database of Contaminated Sites.


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    2010 Outreach

  • FHR continues to provide bottled water to those impacted.
  • Flint Hills completes a comprehensive search for drinking-water wells and sampling effort.
  • City of North Pole municipal wells are tested weekly from October 2009 through February 2010.
  • February -The federal Agency for Toxic Substances and Disease Registry (ATSDR) publishes a health consultation recommending a public health action level of 25 parts per billion of sulfolane in drinking water.
  • March - DEC forms a collaborative Technical Project Team (TPT) to provide comprehensive and coordinated oversight for the investigation. The team consists of government and industry representatives and multidisciplinary experts.
  • April - Flint Hills installs new wells for the City of North Pole public water system, even though sulfolane concentrations in the former City wells were consistently below 10 parts per billion.
  • Rigorous inspections of the refinery are conducted to identify any potential ongoing sources of sulfolane contamination.
  • DEC and FHR develop a site characterization work plan to investigate the extent contamination and evaluate exposure.
  • The TPT completes a garden sampling project involving several local gardeners to investigate if sulfolane accumulates in plant tissues.
  • September - FHR begins a pilot study of a granular activated charcoal (GAC) technology for removing sulfolane from groundwater.


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  • The sulfolane plume is found to extend 3 miles downgradient from the refinery and approximately 2 miles wide at its widest area (off-site). Sulfolane is detected in private wells above and below permafrost.
  • January - New North Pole public drinking water system wells begin operation.
  • February - Flint Hills submits a feasibility study to build home treatment systems to treat sulfolane using granulated activated carbon filters.
  • May - ATSDR develops action levels for sulfolane in drinking water, with the most protective level being for infants, at 20 parts per billion, in its “Health Consultation – Sulfolane
    • DEC issues guidelines for the groundwater analysis of sulfolane, creating specific procedures that all laboratories analyzing water for sulfolane must meet.
  • August - The groundwater monitoring network continues to be expanded on and off the refinery property for horizontal as well as vertical delineation of contamination.
  • Available private well records and logs are reviewed to enhance the understanding and interpretation of the private well sampling data.
  • FHR identifies past spills and releases through a records review, which indicates that sulfolane releases into groundwater were mostly from subsurface wastewater containment systems.
  • FHRA inspects and tests the refinery sump systems, correcting weaknesses, encouraging plant-wide spill prevention and control, and initiating preventative maintenance programs.
  • Surface water samples collected from the refinery gravel pits and the Badger Slough do not contain sulfolane.
  • FHRA and its contractors continue work to provide an alternate water supply to the homes outside the City of North Pole limits with wells impacted by sulfolane: The residential and commercial locations have one of the following permanent solutions: an in-home water treatment system, a bulk water tank or long-term bottled water delivery services. Bulk tanks are provided to home for gardening water, if requested.


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      2013 Outreach

      • February - The sixth newsletter is published.
        • Open house held at North Pole Plaza Mall.
      • June - The seventh newsletter is published.
        • DEC letter and survey mailed to all property owners in affected area, living in- and out-of-state, expands communication with those affected.
      • June - DHSS issues a fact sheet “Health Recommendations and Next Steps,” summarizing recommendations to date.
        • State Agency open house, at North Pole City Hall, with DEC staff and team, and DHSS representatives.
      • August – September - Responses sent to property owners who responded the June survey with questions issues raised.
      • December - The eighth community newsletter is posted on the website.

  • FHRA conducts an additional door-to-door survey of homes on City water in the affected area to ensure people are aware of the DHSS recommendation to use non-impacted water to water vegetable gardens.
  • Summer - FHRA conducts a permafrost mapping survey to better understand permafrost formations, improving understanding of groundwater movement and aiding in predicting plume behavior.
    • About 80 additional monitoring wells are installed and about 240 soil and water samples collected over the summer and fall.
    • UAF continues working with DEC conducting research on the degradation of sulfolane and transport of sulfolane through discontinuous permafrost.
    • Soil and surface water from gravel pits are sampled for sulfolane.
    • Soil is sampled from lawns and flower gardens watered with sulfolane-containing water.
  • November
    • DEC's Spill Prevention and Response Division gives conditional approval to FHRA’s Human Health Risk Assessment and establishes a cleanup level of 14 parts per billion (ppb) for sulfolane at the North Pole Refinery.
    • Gravel pit study results show that the surface water in gravel pits does not contain sulfolane, and there's no danger in moving gravel to other areas.
  • December


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    2014 Outreach

  • January - The National Toxicology Program (NTP) begins studies on the health effects of sulfolane to evaluate aspects not previously researched.
  • March
    • The State files a lawsuit against the current and former owners of the North Pole Refinery. DEC continues oversight of the site investigation and cleanup.
    • DEC issues a garden soil study report from testing indicating that using sulfolane-contaminated water on gardens does not leave residual sulfolane in the soil.
  • April - DEC's Commissioner “vacates” the Spill Prevention and Response Division’s 14 parts per billion cleanup level decision. This decision meant no cleanup level number was in effect. He also gave instructions for the Division’s further consideration and explanation in a setting a new cleanup level.
  • June – FHRA submits a supplement to its Human Health Risk Assessment, proposing a cleanup level of 362 ppb.
  • Summer
    • FHRA expands the groundwater extraction system at the refinery as part of their proposed interim remedial actions.
    • UAF continues working with DEC conducting research on the degradation of sulfolane and transport of sulfolane through discontinuous permafrost.
  • July - DEC develops an interim best management practices plan to assist with the management of dewatering activities near or within the sulfolane plume. (See June 2014 newsletter for summary, also see the document)
  • The sulfolane plume's approximate size to date is 3.5 miles downgradient (northwest) from the refinery, 2 miles wide, and over 300 feet deep.
  • September 16-17 – At SPAR Division’s request, an independent, expert peer review of the available reference doses for sulfolane is conducted in Fairbanks by the non-profit organization Toxicology Excellence for Risk Assessment (TERA). This is part of the division’s detailed analysis ordered by the Commissioner. A reference doses is one of a number of factors used in calculating a cleanup level.
  • October - DEC approves an Onsite Cleanup Plan proposed by Flint Hills Resources for contaminated soil and groundwater within the boundaries of the refinery property.
  • December
    • TERA report is released, concluding that none of the reference doses (or toxicity values) aligned perfectly with the recommendations of the expert panel. Although the report concluded that the value proposed by FHRA most closely aligns with the panel’s conclusions, the experts identified a number of uncertainties about the toxicity of sulfolane including lack of reliable, long-term studies on the health effects of long-term exposure to sulfolane. (See the report).
    • DEC meets with the National Toxicology Program and learns they plan to begin long-term studies to address the remaining uncertainties about the health effects of exposure to sulfolane.


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  • August -  The 2014 Onsite Cleanup Plan is modified to cease operation of the western groundwater extraction and treatment system, due to low levels of influent contamination. Operation of the original (eastern) onsite treatment system and groundwater monitoring continues.
  • September - Information on property concerns regarding sulfolane contamination is provided to the public through the website.


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2017 Outreach

  • February
    • Flint Hills Resources Alaska and the State of Alaska announce on February 7th, 2017, that they will be working with the City of North Pole to significantly expand their piped public water system to provide sulfolane-free drinking water to residents impacted by the sulfolane groundwater plume. (See fact sheet on the settlement agreement).
    • A 2017 Onsite Cleanup Plan is released.
  • July - Under the 2017 Revised Onsite Cleanup Plan, operation of the onsite groundwater recovery and treatment system is replaced by intensive groundwater monitoring. Contingencies are in place to resume active treatment if the plan goals are not met. (See fact sheet on the Revised Onsite Cleanup Plan)





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Sulfolane Use in the U.S. and at the former North Pole Refinery

    Sulfolane is an industrial solvent used to extract aromatic compounds from hydrocarbon mixtures and to purify natural gas. It is on the U.S. EPA's High Production Volume Chemical List that indicates the volume of sulfolane either manufactured or imported into the U.S. exceeds one million pounds per year.


    At the the former North Pole Refinery, sulfolane was used to extract aromatics from naptha to produce gasoline. In the aromatic extraction process, sulfolane was initially mixed with the petroleum feedstock (naphtha and light distillates). The sulfolane extracted the aromatics from the feedstock, and the aromatic-laden sulfolane was sent to a stripper for aromatic removal before returning to the extraction unit. Sulfolane as used in the refining process was dissolved in gasoline but it is more soluble in water, which allowed it to dissolve in, and be carried along with groundwater.

    There are at least 150 similar extraction units in the U.S. Sulfolane use in North Pole began in 1985. While gasoline was the only product that required the sulfolane extraction process, sulfolane may have migrated into other refinery products due to incidental carry over¯ through the refinery's piping system. Fuels that may have contained sulfolane in the past include #1 fuel oil (jet fuel) and #2 fuel oil (diesel fuel). Only gasoline was monitored for sulfolane content as it was the only fuel produced at the refinery with a sulfolane specification.

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