Division of Spill Prevention and Response

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Cook’s Tesoro


Incident location map. Summary Date: November 10, 2004 View detailed information from database on this site.arrow
Status: Active Database Name: Cooks Corner Tesoro - Sterling
Location: Sterling, AK Latitude: 60.535500 Longitude: -150.744800
DEC Contaminated Sites Contact: Paul Horwath, Project Manager - 907- 262-5210 ext. 250
Contaminated soil was excavated to 20 feet below the ground surface

Interim cleanup measures were initiated in 1990. Contaminated soil was excavated to 20 feet below the ground surface, with approximately 3300 cubic yards of soil removed. (DEC photo)

 

 

An impermeable liner was installed under the soil pile.

The excavated soil was initially stored and treated behind the Cook's Tesoro facility. An impermeable liner was installed under the soil pile. The excavated soil was eventually hauled to John Cook's homestead site several miles east of the station, for further treatment and disposal. (DEC photo)

Description

 

Fuel contamination (primarily gasoline) was identified at Cook's Tesoro facility in 1989 during assessment work for expansion of the Sterling Highway through Sterling. The site is about 950 feet north of the Kenai River and 1600 feet east of the Moose River.


DEC hired a contractor to investigate the site in 1989, and interim cleanup measures began in 1990. Contaminated soil was excavated to 20 feet below the ground surface, with approximately 3300 cubic yards of soil removed. The soil was treated and disposed of at John Cook's homestead property, several miles to the east of the Cook's Tesoro facility. Inaccessible areas of highly contaminated soil remained under and adjacent to the building and beneath the original fuel tanks. Soil contamination also remained directly beneath the excavation area down to the groundwater at 25 feet.


The monitoring data indicates a declining trend in the contaminant levels over the past 15 years. The cleanup efforts conducted in the early 1990's, along with natural attenuation, have resulted in a stable or decreasing level of contamination. The groundwater monitoring program defined the extent of the plume, and it consistently indicates no detection of fuel contamination in drinking water wells and/or the Kenai River.

 


Public Health and Environmental Concerns

 

The primary contaminants of concern are the numerous petroleum constituents present in gasoline. The primary risk posed by these contaminants is groundwater contamination and the potential impact to drinking water wells. DEC has also looked at the possible risks to ecological concerns if contamination migrated to the Kenai or Moose Rivers. The monitoring data indicate that there are no impacts to drinking water wells or migration of contamination to either river.

 


Uncontaminated dirt was filled into the hole at Cook's Tesoro station

Uncontaminated dirt was filled into the hole at Cook's Tesoro station, where contamination remains inaccessible under and around the building and beneath the excavation area down to the groundwater at 25 feet below the ground surface. (DEC photo)

 

 

The soil stockpile behind Cook's Tesoro was treated through bioremediation, including aeration.

The soil stockpile behind Cook's Tesoro was treated through bioremediation, including aeration. (DEC photo)

Current Status

A groundwater treatment system was installed at the Cook's Tesoro facility in the spring of 2004 in an effort to treat a highly contaminated portion of the site. The treatment system will only operate during non-freezing seasons. DEC will keep track of the operation of this treatment system, and monitor groundwater quality both on and offsite, in the effort to evaluate the effectiveness of the groundwater treatment operation. The residual dissolved-phase groundwater contaminant plume extends across the Sterling highway. Contaminant concentrations are diminishing over time. There is no indication groundwater contamination is impacting drinking water wells or the Kenai River .


Two new monitoring wells were installed and two drinking water wells were sampled in December 2002 and April 2003. The sample results did not detect contamination in either of the new monitor wells or the drinking water wells. The groundwater monitoring data indicate elevated levels of contamination are still present but there is no risk to human health or the environment under current conditions.


The groundwater will continue to be monitored to ensure the plume doesn't expand and pose a risk to human or ecological receptors. Long term monitoring will be required until the contaminant concentrations achieve the established cleanup levels for this site.

 

 

More Information

 

  • Site Summary, (PDF 123K), January 2003

  • Site Summary, (PDF 14K), March 2002


Map of Sterling.