Turning on the tap for a clean glass of water is a luxury many Americans take for granted. Though TransCanada Corporation promises minimal spillage and environmental impact through improved safety features in its plans to install a 1169-mile-long, 36-inch-wide pipe through the grasslands of Canada and the United States, risking this natural resource is one of the many considerations President Obama examined before vetoing the installation of the Keystone XL oil pipeline. [1,2] After failing to override the President’s veto, Senate Republicans vow to attach it to another bill or hastily pass the legislation.  However, scientists and environmentalists continue to debate the safety of the pipeline in regards to its impact on water and soil quality in the event of spillage.
Alberta, in Western Canada, has recently seen a boom in tar sand extraction which yields diluted bitumen—a thick, oily tar mixed with other lighter petroleum products to ease transport.  The diluted bitumen, or dilbit, must be transported to existing refineries located in the United States near the Gulf of Mexico or to ports in Vancouver, where it can be shipped primarily to burgeoning Asian markets. With 2934 miles of pipeline already in place, the Keystone XL project has the capacity to transport an additional 830,000 barrels of oil per day to southern U.S. refineries. 
Since dilbit is much more viscous than conventional oil, it must be pressurized up to 1440 psi (compared to 600 psi for conventional oil—and 30 psi for car tires) and heated to 158°F to pass through the pipes over such a long distance. Moreover, unprocessed dilbit still contains abrasive particles, is around fifteen times more acidic, and contains five to ten more times sulfur than conventional oil, increasing the probability of a leak or failure of the pipe system that could go unnoticed for weeks. Most of the planned pipe system would be placed ten feet underground traversing remote areas of the Midwest, while other sections would cross important above-ground water resources, including the Missouri, Yellowstone, and Platte Rivers (Figure 1). 
After narrowly being diverted from the Sand Hills region of Nebraska—an ecologically fragile zone characterized by grass-covered sandy hills—the Keystone XL Pipeline is slated to go through regions of the Ogallala Aquifer, which provides irrigation for nearly twenty percent of agricultural land in the United States. [5,6] With so much at risk, scientists dispute both the rate of pipeline failure and the effect of dilbit contamination on soil and water landscapes.
TransCanada promises 57 security features—both in safety checks and the mechanics of the system —to ensure the safe passage of oil. Moreover, by committing over $900 million dollars per year for safety protocols and maintenance, TransCanada puts the official spill estimate at 0.00013 spills per year per mile, with only 11 total per 50 year lifetime [2,5]. They anticipate most leaks to be small and quickly visible by aerial detection and observation protocols carried out every two weeks. 
John Stansbury, Ph.D., Associate Professor of Civil Engineering at University of Nebraska-Lincoln, believes these statistics are severely understated. By compiling historical data, he expects the spill count to hover around 91 spills per 50 year lifetime, or 0.0019 spills per year per mile, nearly tenfold the TransCanada estimate. Moreover, he fears most of these spills will not be detected for long periods of time. Buried in the ground, spills and leaks in the pipeline may not manifest themselves for many weeks to be visible by an aerial inspection; it could take 90 days for leaked petroleum to reach the surface. In such a scenario, a moderately small leak would release 7.9 million gallons of dilbit into surrounding soil. Finally, Dr. Stansbury points out that the pipe wall is thinner than in previous pipeline projects and the substance carried is under higher pressure and more corrosive, increasing the likelihood of a leak relative to the previous estimation. 
In the event of a spill
Most of the pipeline will be underground, where petroleum can seep into surrounding soils and potentially groundwater. Dilbit is primarily composed of large hydrocarbons that will be trapped in surrounding soils and sediments. Smaller hydrocarbons, such as benzene, make up around 1% of dilbit and have the potential to permeate deeper underground. If left unattended, a leak could contaminate thousands to millions of gallons of water during a rainstorm, making cleanup efforts difficult. 
James Goeke, Ph.D., emeritus professor at the University of Nebraska-Lincoln, posits such a spill event poses little threat to the Ogallala Aquifer as a whole. Goeke argues water below ground acts much like water above—it flows downhill. Since most of the Keystone XL pipeline is to be built west, downhill, from the Ogallala aquifer, widespread contamination is highly unlikely. Moreover, the high viscosity will prevent the vast majority of petroleum from oozing far from the spill event.  According to the U.S. State Department, spills will be localized to a few hundred feet around the spill, assuming no accumulated rainfall. However, around 2500 groundwater wells are located near the proposed pipeline, which will need to be closely monitored for local contamination. 
Leaks in above-ground rivers and streams pose the most tangible threat to human and animal life. The pipeline would cross 56 rivers, and spills in these moving bodies of water could exacerbate the spread of dilbit.  In 2010, Enbridge Energy Partners discovered a leak in their Michigan pipeline, releasing 843,000 gallons of oil into the Kalamazoo River. A downpour flooded the dam, carrying with it oil 35 miles downstream. Clean up efforts are still continuing today, resulting in 33,710 cubic yards of oil-contaminated waste removed from stream beds. 
Though the oil is going to be harvested and consumed regardless of the Keystone XL pipeline construction, Americans must be mindful of the impact petroleum transportation has on the environment. If Congress manages to push the Keystone XL pipeline bill through the legislature, measures and protocols must be followed to ensure the safety and preservation of our natural resources.
Figure 1 ~ Location of the proposed Keystone XL pipeline. 
Adam Riesselman is a G1 in the Bioinformatics and Integrative Genomics program.
 Obama Vetoes Bill Pushing Pipeline Approval (New York Times) http://www.nytimes.com/2015/02/25/us/politics/as-expected-obama-vetoes-keystone-xl-pipeline-bill.html
 TransCanada http://www.transcanada.com/
 GOP-led Senate fails to override Obama’s Keystone veto, lawmakers say fight not over (Fox News) http://www.foxnews.com/politics/2015/03/04/gop-senate-fails-to-get-enough-votes-to-override-obama-keystone-veto-says-fight/
 KeystoneXL Assessment (Ensys Energy) http://keystonepipeline-xl.state.gov/documents/organization/182421.pdf
Analysis of Frequency, Magnitude and Consequence of Worst-Case Spills From the Proposed Keystone XL Pipeline (University of Nebraska-Lincoln) http://watercenter.unl.edu/downloads/2011-Worst-case-Keystone-spills-report.pdf
 New Keystone XL Route: Out of the Sandhills, but Still in the Aquifer (Reuters) http://www.reuters.com/article/2012/04/26/idUS339164205320120426
 The Pipeline Poses Minimal Risk to the Ogallala Aquifer (The New York Times) http://www.nytimes.com/roomfordebate/2011/10/03/what-are-the-risks-of-the-keystone-xl-pipeline-project/the-pipeline-poses-minimal-risk-to-the-ogallala-aquifer
 Draft Supplementary Environmental Impact Statement (U.S. Department of State) http://keystonepipeline-xl.state.gov/draftseis/index.htm
 Dredging To Continue in 2014 at Morrow Lake and the Delta (United States Environmental Protection Agency) http://www.epa.gov/enbridgespill/
 Keystone XL Pipeline Map (Washington Post) http://www.washingtonpost.com/wp-srv/special/business/keystone-xl-map/images/keystone-xl-map.jpg