South Cass Lake Program
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Frequently Asked Questions
Q: What is the South Cass Lake pumping station site?
A: Enbridge operates the South Cass Lake pumping station as part of its extensive petroleum pipeline system extending across Canada and the United States. Crude oil is carried to refineries for processing into gasoline, diesel, fuel oil, motor oils and other petroleum products.
Q: How did the leak happen?
A: Enbridge discovered a leaking flange — a type of connection in the pipeline — in 2002 during a routine leak detection process. The leaking flange, which was caused by normal wear and tear, was repaired. Some leakage might be from historical operations, before the leak detection program was started.
Q: What has been done to clean up the site so far?
A: Approximately 304 yards of soil were removed after the leak was discovered and repaired. An investigation of the surrounding soil and groundwater was completed and identified that an area of crude oil remains at the top of the water table, about 28 feet below the ground surface.
Q: Are any residential wells at risk for contamination?
A: No. As part of the studies, all wells within 1 mile of the site were identified, and none were down gradient of the site within ½ mile of the spill. The extent of the contamination at the site is all within about 200 feet of the spill and is monitored with monitoring wells.
Q: Are any lakes or wetlands at risk for contamination?
A: No. The extent of contamination is well understood and is not anticipated to reach any surface water bodies.
Q: Is the contamination spreading?
A: This is being determined by ongoing sampling of the monitoring wells at the site and by measuring the thickness of oil in wells within the spill boundaries. The oil itself appears to be stagnant due to its high viscosity. We are monitoring conditions for a plume, an area of contamination that forms around the oil when chemicals dissolve out of the oil and into the groundwater. At this time, the extent of the dissolved plume appears stable, and ongoing sampling will tell us if this changes.
Q: What’s next for the clean up?
A: Enbridge has hired an environmental consultant to evaluate the clean-up options. Enbridge is working cooperatively with the Leech Lake Band of the Ojibwe Department of Resource Management (LLBO DRM). The evaluation, called a feasibility study, includes examination of the scientific feasibility, the potential health and environmental risks and the cost effectiveness of different clean-up technologies.
Q: Where is the contamination?
A: The oil is at the top of the water table at a depth of about 28 feet below ground surface. This
illustration
shows a cross section, or side view, of the contamination. As the picture shows the oil soaks through the soil and floats on the water table. A plume of dissolved petroleum chemicals forms outside of the oil.
Q: Why can’t you just pump the oil out?
A: Some oil can be removed by pumping or other methods. However, much of the oil gets trapped between the soil grains in the aquifer. Because the oil is much thicker than water pumping tends to remove water from the aquifer but leaves the oil behind. It’s similar to trying to clean an oil-based paint from a paint brush, the paint sticks to the bristles like the oil sticks to the soil grains. This
link
shows a microscopic view of an oil droplet trapped in soil.
Q: What will eventually happen if the oil is not removed?
A: Fortunately, the oil will stay in its current location due to the fact that it is more viscous than water. Contaminants that dissolve into the groundwater will be consumed by natural bacteria in the aquifer. Over time the oil will get more viscous as it ages and fewer contaminants will dissolve into the groundwater.
Q: What is a leaking flange?
A: A flange is a common type of connection between two pipes. The flange was buried below the ground and over time began leaking. Enbridge regularly inspects all it’s sites for leaks and discovered the leak in 2002. The flange was repaired and an investigation of the leak was completed. Enbridge dug up the contaminated soil around the flange.
Q: Why not just dig up all the oil?
A: Excavation is one possible approach to the problem and is being evaluated as part of the feasibility study. The site is active and there are extensive underground piping and other structures that would make excavation very difficult and risky while the pumping station is active.