A paper came out this week in Environmental Science and Technology, probably my favorite technical journal, suggesting a “risk-managed route” for the Keystone XL pipeline. The original route made enough stakeholders in Nebraska nervous about their groundwater supplies that the governor requested President Obama to deny the Presidential Permit, and so it was done. Keystone has a new proposed route, which will avoid much of the Nebraska Sandhills, but still go through some ecologically sensitive areas. The authors of this paper propose a route that avoids surface water crossings in the canyons of the northern part of the Ogallala aquifer, and instead intentionally crosses spray-irrigated, row-cropped land underlain by nitrate-contaminated groundwater. The route eventually connects with the existing Keystone 1 pipeline north of the Platte River, rather than the proposed connection in Steele City, NE.
Now, I’m sure that Keystone has its own agenda for why it chose the route it did, and there are parts of this “risk-managed route” that are left unmentioned in the paper (it’s only 5 pages, so it can’t cover everything). That said, the authors’ proposed route has an interesting idea as far as the irrigated cropland goes. They assume that pipeline spills are inevitable (over the past 10 years, they cite statistics of 0.8 spills per 1000 miles of pipeline, averaging 364 barrels of oil), and that dilbit will partition into the part that volatilizes (evaporates away) and the part that floats on the water surface (light components called “light non-aqueous phase liquids” or LNAPLs). The existing irrigation infrastructure is already set up to deal with LNAPL spills in the groundwater: the irrigation wells can extract the water+hydrocarbons, and the irrigation sprayers can enhance volatilization of the components pumped out of the ground. Interesting thoughts, and true.
The big red flag in my mind is the actual composition of the dilbit (diluted bitumen) to be carried in the pipeline. Normal crude oil is largely lighter than water, and does in fact float. But bitumen is more like tar, and it’s diluted with lighter hydrocarbons so it can even flow in pipelines. I don’t know if bitumen composition is a trade secret or something (I couldn’t find much information), but it’s possible that it would sink under the water table (making it a dense non-aqueous phase liquid, or DNAPL) rather than float. In fact, the Enbridge spill in Michigan suggests that dilbit will, in fact, sink, though in that case, the dilbit got mixed in with sand and sediment that caused it to sink into the riverbed along 40 miles of the Kalamazoo River. There’s not much mixing like that in groundwater — things are pretty static.
But think about this: LNAPLs are easier to remediate than DNAPLs, based on the physics of water and non-aqueous phase liquids. I found a statistic that the average spill cost is ~$2,000/barrel for normal crude oil, but the spill in Michigan is already past $29,000/barrel. Multiply that by 364 barrels/average spill, and you’re talking a $10.6 million starting point, on average. That’s an expensive project.
I guess my take-home message is, I like the thinking outside of the box in the paper, but if dilbit is, in fact, DNAPL rather than LNAPL, we need to do a lot more due diligence and risk mitigation before we approve anything.