Intelligently routing the Keystone Pipeline

Fig. 1. Geochemical zones at the 1979 Bemidji crude oil spill.  From Delin et al. (1998).

Article summary 

Spalding and Hirsch. 2012. Risk-Managed Approach for Routing Petroleum  Pipelines: Keystone XL Pipeline, Nebraska. Environ. Sci. andTech. 46:12754−12758.

          The controversial Keystone pipeline would transport tar sands diluted bitumen (dilbit) over 3,460 km, from Hardisty, Alberta, Canada, to ports in Texas. Environmental concerns involve the impact of large-volume spills on the Ogallala aquifer in Nebraska and the fragile soils of the Sandhills. Two mechanisms of residual petroleum hydrocarbon (PHC) transport to aquifers exist, and are said to be likely at large releases: i) leaching of aqueous soluble PHC ii) after liquid dilbit reaches the capillary fringe, the lighter aqueous phase  comprised of benzene, toluene, ethylene, and xylene (BTEX) is separated from bitumen and slowly released, forming a long-lived plume. The nonaqueous phase floats on the water table. Polyaromatic hydrocarbons are higher in concentration in dilbit than in gasoline. However, as they are extremely hydrophobic, movement into the vadose zone is very restricted. The PHC of greatest concern in groundwater contamination is BTEX. This PHC is notoriously difficult to clean up and contains benzene, a known carcinogen, at concentrations of .03 to .3% in dilbit. 

The first proposed Keystone XL route was rejected on January, 2012. The risk-managed route (RMR) was proposed as an alternative route which minimizes impacts on the fragile soils of the Sandhills and on the Ogallala aquifer, which provides potable water for 85% of Nebraska’s population.
         Spray irrigation is considered to be an effective remediation strategy for volatile organic contaminants such as BTEX. The RMR avoids water tables < 6 m and attempts to go through Nebraska’s most intensively-irrigated agricultural regions (Fig. 1). Spray irrigation is considered to be an effective remediation strategy for volatile organic contaminants such as BTEX. The Keystone I mainline corridor avoids all but the most easterly portions of the Ogallala aquifer and bypasses the majority of high-water-table bottomlands. Moreover, since groundwater flows east in this region, contamination of the Ogallala would be avoided.  In addition, the RMR is strategically situated over land underlain by groundwater with high nitrate contamination. Elevated nitrate levels, along with dissolved oxygen, are suspected to enhance biodegradation of PHCs. As groundwater with high nitrate tends to be associated with shallow water tables and coarse-textured soils, this would likely be where most PHCs reside in the event of a large-volume spill.    

                

     Fig 2. Depth to groundwater and pipeline routes overlying the  
       controversial areas in NE. From Spalding and Hirsch (2012).