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Silvertip Oil Spill

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On July 1, 2011, an estimated 1,500 barrels, or 63,000 gallons of crude spilled into the fast-moving, flood-stage Yellowstone river when ExxonMobil’s Silvertip Pipeline broke near Laurel. At the time of the discharge, the Yellowstone river was at the peak of a 30-year flood and the river was flowing out of its banks.

The pollution was worse near the source of the spill at Laurel, 20 miles upstream from Billings. However, scoping, or SCAT teams, for Shoreline Cleanup Assessment Technique, found oil as far as 70 miles downstream from the spill site. 

Following initial emergency response activities, ExxonMobil Pipeline Company (EMPCo) conducted cleanup and other actions with oversight and direction from the U.S. Environmental Protection Agency (EPA), DEQ, and other federal, state, tribal, and local entities. After initial cleanup activities, DEQ and EMPCo entered into an Administrative Order on Consent (AOC) in early 2012 that required EMPCo to conduct additional monitoring efforts and additional cleanup as identified by DEQ, reimburse State agencies' costs regarding the Discharge ($760,390.61), and pay a penalty of $1.6 million, with $300,000 to be paid in cash to the State's General Fund and the remaining $1.3 million to be spend on Supplemental Environmental Projects (SEPs). 

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 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 human health 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 did not appear to threaten groundwater resources or private water wells.     

After the release, EMPCo cleaned up crude oil on surface water. Following surface water cleanup, various entities 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 does not pose a continued risk to public health 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 previously deposited in river sediments or soil is now below screening levels or other applicable criteria and does 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 human health 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. 

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)