Site Cleanup and Monitoring
Updated: May 1, 2026
Overview
Contamination associated with historical oil refining activities at the former North Pole Refinery (now Marathon Terminal), located about 15 miles east of Fairbanks, has affected groundwater used as a source of drinking water in the North Pole area, in addition to the land and water on the former refinery property. The refinery operated from the late 1970s until it shut down in 2014. Petroleum product leaks from aboveground storage tanks began in the 1970s.
In the 1980s, groundwater on the refinery was found to be contaminated with petroleum compounds, and the refinery began treatment and monitoring of the groundwater and further characterizing the contamination. In 2009, the industrial solvent sulfolane, which was used in the refining process, was detected in drinking water wells off the former refinery property. In 2018, per- and polyfluoroalkyl substances (PFAS) used in fire-fighting foams on the former refinery were detected in groundwater off the property. The sulfolane groundwater plume is approximately 2 miles wide, 3.5 miles long and over 300 feet deep, and it continues to migrate gradually northward. The boundaries of the PFAS plume have not been fully evaluated.
On the former refinery property, fuel product and sulfolane remain trapped in the soil and groundwater. Groundwater monitoring through 2024 shows no evidence of petroleum compounds migrating off the property above Alaska cleanup levels. Sulfolane continues to migrate beyond the property line below levels allowed under the 2017 settlement agreement (400 parts per billion).
For PFAS, recent sampling shows PFAS above DEC’s soil and groundwater cleanup levels on the former refinery property and PFAS in groundwater above DEC’s action level migrating off the property. In late 2024 Williams removed approximately 1,900 tons of soil containing PFAS from a former fire training area on the property. Post-excavation sampling showed a small area of soil remaining above the cleanup level; this contamination is to be addressed in 2026.
In late 2025, Williams initiated a pilot study, under a DEC-approved work plan, to remove PFAS from groundwater on the refinery. The pilot test evaluation is ongoing through 2026.
Recent information regarding contamination off and on the former refinery property can be found at the links below.
Alternative Water Solutions
In response to the sulfolane contamination, the refinery’s then-owner Flint Hills Resources Alaska (FHRA) began providing affected residents and businesses with alternative drinking water solutions in 2009. They also began sampling and other activities to find out how far the sulfolane had spread. Sulfolane was found to have impacted approximately 350 drinking water wells. FHRA provided affected properties with connections to city water (if available), bulk water tanks, bottled water, or point-of-entry (POE) treatment systems to remove sulfolane from their well water. Properties in a “buffer zone” beyond the sulfolane plume were provided interim bottled water to protect against possible migration of the sulfolane. Sampling conducted in 2018 showed that the alternative water solutions that provided protection from sulfolane were also protecting residents from PFAS in their well water.
In February 2017, the State of Alaska, FHRA, and the City of North Pole reached an agreement to expand the City’s piped water system to all improved properties located within the sulfolane plume or in its anticipated migration path. By the end of 2020, all eligible property owners were offered connection to the service and were able to phase out the use of contaminated groundwater wells. Most property owners were eligible to connect at no cost, depending upon the land’s location and improvement status. The expanded system provides permanent protection from contamination in drinking water.
In 2024, Williams Alaska Petroleum, Inc. (Williams), a previous owner of the former refinery, began evaluating properties near the former refinery that are not connected to municipal water for possible alternative water supplies. Owners of properties within or near the sulfolane groundwater plume and not connected to municipal water are being contacted by Williams or their consultants annually. Wells with detectable levels of sulfolane may be eligible for alternative water or connection to city water. The approved work plan may be found on the Documents page.
Cleanup and Monitoring
Summary
Current cleanup and monitoring actions and plans are listed and described below
- Work plans and reports can be found on the Documents page.
Although site characterization is the first step in the state’s cleanup process, discussion of this step follows the more recent monitoring and cleanup reports. For sulfolane and petroleum, site characterization activities were mostly concluded in 2013, although PFAS site characterization is ongoing.
- For protection of properties developed in the future or ones located beyond the expanded piped water area, long-term groundwater monitoring off the former refinery property tracks the sulfolane plume’s migration and concentrations.
- On the former refinery property, groundwater monitoring tracks sulfolane and petroleum concentrations.
- For PFAS, site characterization activities are ongoing to evaluate PFAS contamination on and off the former refinery property. Interim remedies were implemented in 2024 and 2025 to address some of the PFAS contamination on the refinery property.
Long-Term Groundwater Monitoring Reports
Under DEC oversight, FHRA currently collects groundwater samples from wells located on the former refinery, and Williams collects groundwater samples from wells located off the former refinery to monitor contaminant plume migration and trends. Recent results are summarized on the project home page and reported as described below.
- Onsite monitoring results are compiled into annual reports, and a five-year review was completed after the 2022 monitoring event. Reports are available on the Documents page, Onsite Plume.
- Offsite monitoring results are compiled into annual reports, and a five-year review was completed after the 2022 monitoring event. Reports and are available on the Documents page, Offsite Plume.
- Maps of the results of groundwater monitoring are posted on the Maps page, with the most recent at the top.
PFAS Groundwater Monitoring Reports
The extent of the PFAS contamination on and off the former refinery has not been fully evaluated. On the former refinery property, site characterization activities were initiated in 2020 and continue presently (see Site Characterization, this page). Off the former refinery, PFAS were discovered in groundwater during a 2018 investigation. Follow-up activities include an evaluation of uptake of PFAS into garden produce irrigated with PFAS-contaminated groundwater; sampling of three rainbow trout collected from Kimberly Lake, northwest of the former refinery; and additional groundwater and surface water sampling in 2023-2024. Recent results are summarized on the project home page and reports and maps may be found on the Documents and Maps pages:
Onsite Cleanup
In July - October 2024, DEC approved Williams’ evaluation of potential remedies and work plan for interim remedial actions to address some of the PFAS contamination remaining on the refinery property. The interim remedy was initiated in late 2024.
Until 2017, a groundwater extraction and treatment system operated for many years on the former refinery property. It was phased out of operation and replaced by long-term monitoring in July 2017. The treatment system was initially installed in the 1980s to remove free petroleum product from the subsurface. The system was expanded and upgraded several times over the years to capture and treat contaminated groundwater. After sulfolane was discovered off the property in 2009, the system was significantly expanded to capture sulfolane before it migrated beyond the property boundaries. During its years of operation, the treatment system removed thousands of pounds of sulfolane and petroleum from groundwater, thereby greatly reducing the amount of sulfolane migrating off the refinery property. Limited sampling showed the system also removed some PFAS from the groundwater. Petroleum constituents have not been shown to have migrated off the property. Contingencies are in place to resume active treatment if the Plan goals are not met.
Historically, contamination present in some accessible portions of the former refinery was removed through excavation and offsite disposal. In 2015, three soil excavations removed soil contamination from the former refinery property, including PFAS-contaminated soil from the former fire training area. In late 2024 Williams removed approximately 1,900 tons of soil containing PFAS from a former fire training area on the property. Post-excavation sampling showed a small area of soil remaining above the cleanup level; this contamination is to be addressed in 2026.
Site Characterization
Under Alaska regulations (18.AAC 75.335), the extent of contamination at a contaminated site is to be characterized before proceeding with cleanup. The site characterization requirements generally include investigation activities to determine the types of contaminants present, the source areas, possible risk to people and the environment, the possible need for interim cleanup actions, and the extent of the contamination both horizontally and vertically. The site characterization reports include an evaluation of potential cleanup activities that may be appropriate at the site. More information on the State of Alaska cleanup process is available at the links below:
Multiple site investigations were performed for the North Pole Refinery, beginning in the 1980s, but the 2009 discovery of sulfolane beyond the refinery property instigated a new round of intensive efforts. Investigations of soil and groundwater were performed onsite to evaluate the source and extent of the sulfolane contamination and to refine the understanding of the petroleum contamination. Offsite investigations assessed the size and boundaries of the sulfolane groundwater plume. Hundreds of monitoring wells were installed, and thousands of groundwater samples were collected.
A phased multi-year site characterization of PFAS in groundwater and surface water on the former refinery property began in 2020 and continued in 2022 through 2025 under DEC oversight. Sampling showed PFAS above DEC’s soil cleanup level on the refinery and PFAS in groundwater above DEC’s action level migrating off the former refinery property.
The characterization reports may be found on the Documents page.
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