In 2012, Enbridge was performing an abandonment project for small diameter pipelines associated with crude oil production lease sites in oil fields throughout Enbridge’s North Dakota gathering system. Enbridge’s gathering system extends across northwestern North Dakota into northeastern Montana. The small diameter pipelines (typically 2-inch) connected crude oil production wells and associated tank batteries to Enbridge’s pipeline gathering system. The practice of moving oil through the small diameter pipes into Enbridge’s gathering system terminated more than 10 years ago. Oil from production wells has since been transported off the sites via tanker trucks. The small diameter pipes were therefore no longer necessary and, Enbridge has been disconnecting, also known as abandoning, them from its gathering system pipelines.

Evidence of an historical crude oil release was discovered at the Grenora Dig #12 Site in the Dwyer Field during the abandonment work. The site is on Enbridge’s gathering system right-of-way [Barr, 2012]

1.1.2.1 Location

Site Address: Dwyer Road, Dagmar, Montana
Zip Code: 59219
County: Sheridan
Township: 32N Range: 59E Section: 19 (SE¼ of NW¼)
USGS 7.5-Minute Quadrangle Map: Brush Lake
Latitude: 48.51495 Longitude: -104.10210

The site is located approximately 1/2 mile from Cottonwood Creek; however, much of the area between the site and the river appears to be an adjacent wetland under the Clean Water Act. The release location is less than 50 feet from the wetland. It should also be noted that the site is approximately 5 miles upstream from the Medicine Lake National Wildlife Refuge.

1.1.2.2 Description of Threat

Given the unknown nature of the release and its proximity to the wetland, the OSC has initiated an assessment effort to evaluate the threat posed to the wetland.

1.1.3 Preliminary Removal Assessment/Removal Site Inspection Results

The OSC had determined that additional assessment was necessary after reviewing the initial reports of the abandonment work and discovery of the discharge. To that end, Enbridge had planned to do additional soil removal last summer. Significant rainfall and the discovery of a previously unknown and improperly abandoned line precluded the scheduled work. A small quantity of oil was discovered when the newly discovered line was uncovered. Limited assessment was done by hand boring, with results presented in an August 2013 memo from Barr. It is unknown at this time how much product remains in the newly discovered line.

Enbridge was unwilling to open up someone else's line and was, in any event due to the unexpected discovery, un-prepared to recover even a modest amount of oil if the line was anything other than empty.

The OSC subsequently discovered that the property is a privately held tribal allotment and endeavored to contact the property owner. This process took several months, owing to BIA records only having a mailing address, and the owner traveling extensively. The property owner eventually granted EPA access for assessment purposes. 

The OSC mobilized the START contractor in December of 2014 to conduct geophysical assessment of the site around the abandoned line to locate preferential flow pathways in the subsurface. The effort yielded evidence of a series of paleo channels that, if present, should have collected oil. Please see the START geophysical report on the epaosc.org site for more details.

START was remobilized in April of 2015 to perform limited soil boring activities in the areas of the identified subsurface channels to look for evidence of oil. April was targeted to allow the geophysical report to be finalized and to allow the soil boring to occur before spring thaw. Unfortunately, an early thaw frustrated this effort, resulting in portions of the site being submerged under water. However, START was able to complete borings in a sufficient number of the targeted areas. This effort demonstrated that there is not a significant pool of subsurface oil present at the site, nor did such a pool exist in the past and migrate. Please see the START report on the epaosc.org site for more details.

However, the secondary effort of the assessment was to quantify the threat posed by the improperly abandoned line. The flooded area of the site was directly on top of the line, precluding the use of magnetic location. Fortunately, the utility locator contracted by START as part of the Geoprobe effort has extensive records and was able to provide locational about the line. This information is still being evaluated at this time.