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Silvertip Oil Spill

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On the night of July 1, 2011, ExxonMobil Pipeline Company’s (EmpCo’s) 12-inch Silvertip Pipeline broke in the Yellowstone River where it crosses the river near Laurel, Montana.  An estimated 1,509 barrels (or 63,378 gallons) of crude oil was released into the Yellowstone River.  At the time of the release, the Yellowstone was at the peak of a 30-year flood event, with the river over its banks.  EmpCo has installed a replacement pipeline approximately 40 feet under the bed of the Yellowstone using horizontal drilling methods.

Flood waters carried the crude oil downstream, and into flooded fields, backwaters, and other lands along the river.  Impacts were heaviest close to the point of the release, but visible signs of crude oil were documented at least 70 miles downstream of the spill.  Emergency personnel conducted evacuations of homes along the river.  Response teams set out absorbent booms and pads to mop up oil.  However, due to the Yellowstone’s dangerous flooding conditions, boat crews could not safely get onto the river for several days. 

On July 5, 2011, Governor Brian Schweitzer declared a State of Emergency in the counties downstream of the Silvertip release.  On July 6, 2011, the United States Environmental Protection Agency (EPA) and EmpCo entered into an Administrative Order for cleanup of the release.  Governor Schweitzer made the Montana Department of Environmental Quality (DEQ) the lead State regulatory agency for the Silvertip release.  On August 17, 2011, DEQ issued a violation letter to EmpCo requiring continued cleanup and investigation.  On September 9, 2011, lead agency responsibility for the site transferred from EPA to DEQ. 

Cleanup of the spill occurred systematically.  Field teams surveyed pre-defined areas, mapped oiling conditions, and recommended treatment.  The results of the surveys were transmitted to cleanup crews, who conducted the necessary treatments.  Finally, the field teams re-surveyed the area to determine whether cleanup criteria were met.  Cleanup methods consisted primarily of clipping and bagging oiled vegetation, wiping large objects, flushing objects (stumps, riprap) with water, collecting oil and sheen with absorbent materials, removing oiled debris with heavy equipment, and rubbing dirt onto oily objects (primarily large trees) where wiping was ineffective (to create a barrier between the oil and animals). 

The last emergency cleanup effort took place on November 8, 2011, when the Montana Department of Natural Resources and Conservation (DNRC), with support provided by EMPCo, burned an oiled debris pile on an island in the river.  

On February 28, 2012, DEQ and EmpCo entered into an Administrative Order on Consent (AOC) regarding all future work necessary to clean up the spill, payment of a penalty, and payment of the State’s past and future costs.  Under the AOC, EmpCo agreed to pay $1.6 million dollars in penalties, with $300,000.00 paid in cash to the State’s General Fund and $1.3 million to be paid in the form of Supplemental Environmental Projects (SEPs). 

After emergency cleanup ended in November of 2011, EmpCo performed reclamation of disturbed areas, conducted extensive environmental sampling (soils, sediments, groundwater, surface water, and public water supply), and responded to other issues.  EmpCo prepared a SEP Proposal, and implemented the SEPs to the satisfaction of DEQ.  DEQ determined that the SEPs were complete on March 16, 2015.

DEQ determined that reclamation activities were complete on State lands in August 2013 under the AOC. Reclamation activities included seeding and monitoring trails and other disturbed areas, and scattering woody debris over trails to prevent unauthorized future use. On private property, EMPCo entered into agreements with private property owners regarding reclamation needs.

In May 2013, DEQ determined that no additional sampling of each Public Surface Water Supply (PSWS) along the Yellowstone River starting at Laurel was necessary after tests showed contamination was below cleanup/screening levels.

Under DEQ's direction, EMPCo conducted “natural attenuation monitoring” to photo-document the oil weathering process over time. The effort started in fall 2011, at 45 locations. By the end of summer 2014, oil was still apparent at only 9 of these locations and is still degrading naturally in these locations. These oil stains do not pose an unacceptable risk to public health, welfare or safety, or the environment.

DEQ also required EMPCo to conduct groundwater monitoring. Over 300 private wells were sampled and several monitoring wells were installed in locations where crude oil would have been most likely to impact groundwater. Very few petroleum compounds were detected in this monitoring, and those detected were not compounds found in crude oil. In September 2013, DEQ determined that petroleum hydrocarbons from the discharge were not present in groundwater resources or private water wells and did not pose an unacceptable risk to the public health, welfare or safety, or the environment.     

After the release, EMPCo cleaned up crude oil on surface water. Following surface water cleanup, various governmental entities and EMPCo collected at least 195 surface water samples. In the absence of visible oil, none of the surface water samples exceeded applicable water quality standards or screening levels. In September 2014, DEQ determined that oil from the discharge does not exceed applicable water quality standards and did not pose an unacceptable risk to public health, welfare or safety, and the environment via surface water. 

One of DEQ's primary concerns was the concept of crude oil becoming absorbed or trapped by sediments and debris and settling in the river bed where it might later be released or where it might harm aquatic life. DEQ was also concerned about crude oil that may have deposited in upland areas and impacted surface soils. DEQ has reviewed and analyzed results from approximately 1,325 soil and sediment samples. The results indicate that where oil from the discharge had been deposited in river sediments or soil, those areas are now below screening levels or other applicable criteria and do not pose an unacceptable risk to aquatic life or human health. 

From December 12, 2014, through January 23, 2015, DEQ asked the public to provide input regarding any remaining concerns about crude oil in soils and sediments. DEQ solicited public comment to inform the public of the status of the Discharge, and to ensure any remaining concerns were addressed. DEQ received no comments from the public. 

Although unacceptable risks to public health, welfare or safety, and the environment under the AOC appear to have been adequately addressed and do not pose an ongoing threat, some natural resources have been damaged or lost. The AOC does not address natural resource damages. Natural resource damages will be addressed by the Montana Natural Resource Damage Program and the U.S. Department of Interior. 

DEQ certified termination of the AOC on October 28, 2015.

DEQ’s Groundwater Remediation Program is the lead program for this site.  

Document Description


Cleanup Reports by Area
EPA Documents
Natural Attenuation Monitoring
Sediment and Soil
Surface Water




Laura Alvey

Environmental Science Specialist
P.O. Box 200901
Helena MT  59620-0901
1-800-246-8198 (in-state only)


Jeni Flatow

Remediation Public Information Officer
P.O. Box 200901
Helena MT  59620-0901
1-800-246-8198 (in-state only)