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Environmental Investigation

Plume Boundaries



 

area of concern

Map showing area of concern. Click on map for larger map and more information.

The edges of the plume are now fairly well defined. Monitoring wells installed at Badger Road and Peridot Street and west from that intersection are clear of sulfolane but tests of residential wells in that area have shown low concentrations (below 25 parts per billion). See the map at the bottom of the page for the most current information we have on the extent of sulfolane contamination in the groundwater.


Flint Hills is now testing north of the Richardson Highway and in deepter monitoring wells. As of the end of March 2010, results of tests conducted due east and southeast of the refinery have all shown no detections of sulfolane.


We have no evidence that sulfolane in groundwater is spreading further or moving. The plume is driven by a source -- soil saturated with fuel from old spills at the refinery. The fuel contains sulfolane. Removing this fuel is time-consuming, but it is the most effective way to stop the sulfolane contamination. Ongoing efforts to remove this fuel from the ground are slowly reducing sulfolane in the groundwater. Work has been done on the refinery to ensure there is not an ongoing release of sulfolane, and the refinery is installing more safeguards to ensure no new future releases.


We do not expect concentrations to increase significantly in the plume area. Permanent monitoring wells have been installed to measure sulfolane monthly. This monitoring program will tell us if there is any increase or sign of the contaminant moving further.


There is also no sign that the soil in the residential areas is impacted by sulfolane—only the groundwater. We are evaluating the potential for any other sources of sulfolane contamination besides the refinery, but at this time we are certain the main source is at the refinery. We are also certain that the contaminant is moving off the refinery property in the groundwater, not the soil.

 


Groundwater flow

 

Private wells in areas close to and east of the refinery were not initially tested. We did not expect that sulfolane would show up in these wells. Responding to concerns from residents, however, Flint Hills sampled some of these eastern wells to allay fears. Through the end of March 2010, wells have been tested on Laurance Rd. and Evolyn Drive toward the south end of Blanket Blvd. The lab results listed non-detection for all.


We have much information that indicates a groundwater and contaminant flow direction to the north and northwest, generally paralleling the Tanana River. Monitoring wells on the refinery property have allowed testing over the years for sulfolane and also to determine groundwater flow direction.  These data indicate that the chemical is not traveling to the east. The focus of the sampling has been to the north and northwest in part because of that data. We also have regional groundwater flow information from the US Geological Survey and the new testing off the refinery property. See "Report on groundwater flow" under Documents page.


In general, the direction of groundwater flow may have some variation over time, and its depth may vary seasonally. The chemical and water data we have to date about the refinery and the surrounding areas do not indicate contaminant movement that far to the east, but ongoing monitoring will be used to confirm this over time. The Tanana is a large river and is the primary influence on the groundwater level and movement in the area.  Also sulfolane is a highly soluble chemical, meaning that it wants to be in the water.  This is partially why it has traveled so far to the north.  Other similar chemicals more readily bind to the soils and/or breakdown biologically, or volatilize into the air than sulfolane so do not move as far in the water. 

 


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Sulfolane Concentration in Private Wells, October 2009 through April 15, 2010,
Monitoring Wells March 2010

The map below show three areas of sulfolane concentrations: non-detects, detections between 10 and 25 parts per billion (or micrograms per liter), and detections greater than 25 ppb. Additional sampling and monitoring will determine the exact boundary of the sulfolane plume. Testing of residential wells is still occurring in areas such as around Badger and Peridot Roads where low concentrations are still being found in some wells. Tests of deeper monitoring wells may also change the outer boundaries as well as our larger understanding of the plume. Download a printable version of this map: (PDF 170K) or click on the map.


Other maps are available for download on the Documents page.

Aerial photo of the North Pole Refinery and areas north

Aerial view of the area of investigation of sulfolane in groundwater. The Flint Hills Refinery is the area in light purple.