by Gary Street
Far below the Mackinac Bridge and the surface of the brilliant blue water, lies a set of pipelines that have the potential to become a disaster.
In the last issue of Freshwater Voices I wrote about Enbridge’s operational record. One that includes a spill of nearly one million gallons of heavy diluted bitumen, aka “dilbit,” into Talmadge Creek, near Marshall, MI. (Dilbit is tar sand oil diluted with a material such as naptha or synthetic crude to make the tar sand “pumpable”) Dilbit is heavier than water, sinking to the bottom, making cleanup especially difficult.
Enbridge has two 20 inch lines that lie underneath the waters of the Straits, near the Mackinac Bridge. The lines are nearly 60 years old. Between them, they carry 491,000 barrels per day of crude. Enbridge plans to increase the amount by 50,000 barrels per day in early 2013. This increased flow will increase the line operating pressure by roughly 25%. Can these old lines withstand the increased pressure? Enbridge thinks so. Others, including Freshwater Future, are not so sure. What are the potential impacts on our waters?
If just ONE of the two 20 inch lines crossing the Straits were to rupture, and IF the shut off valves at either side of the Straits were to be closed IMMEDIATELY, the spill would still amount to over 380,000 gallons of crude being released directly into lakes Michigan and Huron!
The National Wildlife Federation has prepared a map of how fast the oil plume would spread. Although this projection only simulates a 3, 6, and 12 hour elapsed spill, at “worst case” discharge conditions, the reality would be much worse.
In the future, I’ll explore the pipeline issue further.
5- It is not practical to shut a large valve “immediately” or even rapidly without causing “water hammer. Water hammer may in turn cause a line to rupture.