The Keystone pipeline, which became operational in 2010, brings about 435,000 barrels of crude oil per day from Albert, Canada, to refineries in Texas. Proposed additions to the pipeline would up that delivery to about 700,000 to 900,000 barrels per day. One of the controversies is that part of the additions to the pipeline would pass over the northeast edge of the Ogallala aquifer in the Sand Hills of Nebraska. See map below. The concern is that possible oil spills from the pipeline could contaminate the aquifer.
While the concern over spills is something to consider, history shows that the pipeline is very safe. According to TransCanada, the pipeline owner, there have been 14 spills since 2010, most of these occurred at pumping stations rather from a ruptured pipeline. The typical spill was 5 gallons and the largest was 21,000 gallons but only 210 gallons escaped the plant.
But what if there is a major rupture where the pipeline passes over the aquifer?
Here is where geology comes in. The geological situation is explained in detail by hydrogeologist Jim Goeke in an article in the (Nebraska) JournalStar. Dr. Geoke has had 40-years of experience with the aquifer.
The first thing you should realize is that the aquifer slopes from west to east, so only the downslope part of the aquifer would potentially be affected by a spill.
Secondly, the geologic nature of the aquifer, which at its shallowest is 300 feet below the surface, would tend to confine any spill to a very small area.