You assume in your question that any contamination will contaminate the water for 30 million Americans. That will definitely not happen. In the unlikely event that ground water is contaminated by XL the effects will be localized. Here are some facts about the aquifer from James Goeke, a research hydrogeologist, and professor emeritus at the University of Nebraska-Lincoln.

"1. The slope of the regional water table is from west to east; the deep waters within the host rocks move persistently downhill eastward. Approximately 80 percent of the Ogallala Aquifer lies to the west of the proposed alignment, “uphill” of the pipeline’s route. Spilled oil could not move upward against gravity.

2. Along much of the alignment, the depth to water is over 50 feet. Sediments above the top of the aquifer contain fine-grained deposits like silts and clays. In a 25-year study of an oil spill near Bemidji, Minn., the Geological Survey reported that “apparently fine-grained layers impeded the infiltration and redistribution of oil.”

3. If areas of the Ogallala were exposed to leaks from the pipeline, the highly varied layers within the rock formation itself would serve to localize the impact of a spill.

4. In places along the pipeline’s route, there are locations where the water table is near or at the land surface. It is my understanding that in these areas, TransCanada will encase the pipeline in a waterproof covering and cement jacket."

The Keystone XL pipeline is safe and should be approved soon.