Sulfolane at the North Pole Refinery (NPR)

The refinery produced its first barrel of product in August 1977; just two months after crude oil began to flow through the Trans Alaska Pipeline. MAPCO purchased the plant in 1980 and expanded its production to include gasoline and asphalt in addition to jet fuel and heating oil. MAPCO merged with The Williams Companies in 1998 and then sold the facility to Flint Hills Resources in 2004.

DEC has documented oil spills into or on land from refinery operations over the plant’s history. Those spills have occurred from leaking storage tanks, leaking sumps, overflow of the wastewater handling pond and certain handling procedures. The volume and extent of the historic spills is such that cleanup activities will be a long-term process.

The 1970 - 1990s

In the late 70s and early 80s, very large but unknown amounts of petroleum product leaked from above-ground storage tanks. These tanks were taken out of service in the mid-1980's. In 1986 DEC issued a Compliance Order by Consent (COBC) and in 1989 the US Environmental Protection Agency (EPA) issued two Resource Conservation and Recovery Act RCRA 3008 Administrative Orders on Consent to then-owner MAPCO. These orders outlined a cleanup and monitoring strategy for the petroleum contamination and RCRA hazardous waste violations. There was no mention of sulfolane, as this chemical was not regulated, and therefore was not seen as a chemical of concern. Monitoring well data indicated that groundwater on the refinery was 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 was tested and found to be unaffected, as was the city water system. At this time, the refinery connected to city water and began treatment and monitoring of the groundwater and performed further site characterization.

Between 2000 - 2010

Site characterization activities during 2000 to 2002 identified an unknown chemical in groundwater monitoring wells. The samples had been collected from a well at which no petroleum-related contaminants were previously reported. Further analysis identified the unknown chemical as sulfolane, believed to be coming from past gasoline spills.
In 2004, Flint Hills purchased the refinery from Williams and submitted a Corrective Action Plan (CAP) to address the on-site contamination. In DEC’s approval of this plan, the groundwater cleanup level for sulfolane was set at 350 ppb. This value was based on available toxicity data and recommendations made by the Canadian Province of British Columbia. This concentration was not exceeded at the refinery boundaries so no active remediation was required, only monitoring. By removing petroleum from groundwater, it was believed that the sulfolane would be sufficiently contained and eventually naturally attenuate. The CAP also defined two interim goals:

1. Remove free-phase product (oil) and dissolved benzene from the subsurface to the extent practicable; and
2. Prevent further contaminant migration.

Pump and Treat technology was selected to achieve these goals. With this technology, groundwater is pumped from wells in the contaminated area and run through an oil/water separator. The oil is separated from the water, collected, and sent back to be refined or disposed. The remaining impacted water goes through an air stripper where hot air strips the fuel constituents out of the water leaving clean water that is then pumped to gravel pits for eventual evaporation or recharge into the groundwater. Groundwater monitoring indicated all contaminants of concern were below cleanup levels at the refinery’s boundary.
Site characterization activities began after sulfolane was detected in fifteen offsite monitoring wells that had been installed in September and October of 2009.  Flint Hills installed the new wells at the northern edge of the property as part of a review of their system performance and overall monitoring program. The results indicated sulfolane concentrations below 350 ppb, but higher than expected. This led to further sampling and the eventual detection of sulfolane in the City of North Pole drinking water well and private drinking water wells. Upon seeing these results, DEC contacted the Department of Health and Social Services (DHSS) for a public health evaluation of sulfolane, since no federal cleanup levels were set for sulfolane. DHSS subsequently contacted the federal health agency, the Agency for Toxic Substances and Disease Registry (ATSDR), and together in February 2010, they recommended that the action level be lowered to 25 ppb until more in-depth studies of sulfolane could be completed.

In a letter to FHR dated March 3, 2010, DEC indicated that based on this new information related to sulfolane, the January 2002 SC/CAP was no longer sufficiently protective. DEC directed FHR to prepare a new site characterization work plan (SCWP) to address the current site conditions and directed FHR to submit a Site Characterization Report and Revised Corrective Action Plan following the completion of the site characterization and prepare an Interim Removal Action Plan (IRAP) to address the light non-aqueous-phase liquid (LNAPL) and sulfolane contaminated groundwater present.

Also, in March of 2010, The Alaska Department of Environmental Conservation’s Contaminated Sites Program created a Technical Project Team (TPT) to provide comprehensive and coordinated oversight for the investigation into the release of sulfolane at the Flint Hills refinery in North Pole. The team consists of experts in the fields of toxicology, engineering, hydrology, environmental chemistry and other relevant fields, and is working to ensure the protection of human health and the environment.

A draft SCWP and a draft IRAP were submitted to DEC on July 23, 2010. DEC provided preliminary approval to begin work described in the documents on August 7, 2010. The final SCWP and IRAP were submitted on September 20, 2010.

2011

Site characterization activities in 2011 continued to fill in the data gaps by identifying areas on and off the refinery property necessary to assist with the long-term monitoring and evaluation of the sulfolane plume. Measures to eliminate releases of all contaminants were prioritized to achieve and maintain source control. Flint Hills Refinery conducted a records review to identify past spills and releases, which indicated that sulfolane releases into groundwater were from subsurface wastewater containment systems. Surface fuel spills have been a less significant contributor of sulfolane to groundwater. Light non-aqueous phase liquids (LNAPLs) present in the groundwater do not appear to be contributing sulfolane to the regional plume.

The monitoring network was expanded to include approximately 200 on-site and off-site groundwater monitoring wells and approximately 50 LNAPL observation wells. The well network assists with delineating the nature and extent of groundwater contamination across the impacted area. The Vertical Profile Transect, completed in November 2011, involved the installation of 6 well nests perpendicular to the long axis of the sulfolane plume to assess the vertical distribution of sulfolane from the water table to permafrost. The expansion of the monitoring network provides a much more detailed cross-section of the onsite plume than what had been previously known through the assessment of sulfolane distribution from the water table to 150 feet below ground surface or permafrost, if present.

FHR focused on inspecting and testing the refinery sump systems , correcting weaknesses found in the system, encouraging plant-wide spill prevention and control, and initiating preventative maintenance programs for plant piping, tanks, and equipment systems. If contamination hot spots or residual source areas to groundwater are discovered, they will be responded to through interim measures or the focused feasibility study evaluations, expected April 2012.

On-site

On-site remediation efforts continued at the refinery. Sulfolane was recovered from contaminated groundwater at an average of 0.5 lb/day. Upgrades to the groundwater recovery system included the addition of a new recovery well, replacing decommissioned recovery wells, installing seven additional LNAPL recovery systems, upgrading pumps and piping , and cleaning well screens in existing recovery wells. One of the major improvements to the onsite groundwater treatment system was the addition of sand filters and granular activated carbon (GAC) vessels to remove sulfolane. Monitoring was conducted during and after the installation of the GAC system, which was installed in June 2011 in accordance with the Interim Removal Action Plan (IRAP) to remove sulfolane from the recovered groundwater. Since the sand filters and GAC system went online in June, recovered groundwater that passed through the treatment system showed sulfolane below the limit of quantitation¹ (LOQ), indicating that the filter system successfully removed sulfolane from contaminated groundwater. This and other measures continue to increase the capacity and recoverability of the treatment system.

The SCWP proposed collecting groundwater samples from several offsite monitoring wells to analyze for parameters that will, over time, provide the information necessary to evaluate the potential for natural attenuation of dissolved sulfolane. Subsurface microbial communities were sampled using Bio-Traps® for site characterization and to evaluate the potential for monitored natural attenuation as a plume-wide remediation strategy. The purpose of this evaluation was to assess the ability and rate of the native microbial community to colonize at low groundwater temperatures. Bacteria and archaea were confirmed to be growing in the Bio-Traps® despite low groundwater temperatures and oxygen levels. These results are the basis for future Bio-Trap® studies that will take a more in-depth look at specific sulfolane-degrading microbes in the aquifer. The University of Alaska Fairbanks Institute of Northern Engineering and Institute of Arctic Biology will also begin research on the factors that control the fate a transport of sulfolane in the groundwater underlying the refinery and adjacent North Pole area in 2012.

Off-site

Major efforts focused on determining the extent of the contamination downgradient and potential movement of the plume and will continue in order to control exposure to sulfolane.

To determine the extent and nature of the downgradient plume, FHR installed approximately 75 offsite monitoring wells (and well nests) to track the plume and define permafrost boundaries to understand plume movement and its horizontal and vertical gradients. The sulfolane plume extends 3 miles downgradient from the refinery and is between 0.25 miles wide (on-site) and 2 miles wide (off-site). Sulfolane mostly occurs at shallow depths off-site, but has also been detected in private wells installed below permafrost. Discontinuous permafrost occurs at various depths both on-site (deep) and off-site (shallow), which creates a unique, localized groundwater flow that is being modeled for improved understanding of the sulfolane plume dynamics. A review of hundreds of private well records and logs was completed to enhance the understanding and interpretation of the private well sampling data, while also contributing the development of a regional groundwater model.

Soil and water investigations were conducted and will be the basis for evaluating additional remediation measures. Surface water collected in refinery gravel pits and the Badger Slough did not contain sulfolane however, pore water was requested for analysis to determine if it is a potential route of contamination through groundwater-surface water interactions.

The Draft Revised Site Characterization Report was submitted by FHR to DEC in December 2011.

Sulfolane Use in the U.S. and at FHR

Chemical structure of sulfolane

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 FHR, sulfolane is used to extract aromatics from naptha to produce gasoline. In the aromatic extraction process, sulfolane is initially mixed with the petroleum feedstock (naphtha and light distillates). The sulfolane extracts the aromatics from the feedstock, and the aromatic-laden sulfolane is sent to a stripper for aromatic removal before returning to the extraction unit. Sulfolane as used in the refining process is dissolved in gasoline but it is more soluble in water, which allows 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 is currently the only product that requires the sulfolane extraction process, sulfolane may migrate into other FHR 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 is monitored for sulfolane content as it is the only fuel produced at FHR with a sulfolane specification.