http://www.huffingtonpost.com/jesse-coleman/tesoro-begins-cleanup-of_b_5642571.html

“However, “full remediation” will only take place down to 8 feet. [Ed. Note: The oil seeped down 42 feet.] This means significant amounts of contaminants (up to 500 ppm) will remain in the soil and water pockets under the wheat field. The root systems of wheat can penetrate 7 feet down, depending on the type of wheat.”

North Dakota Pipeline Oil Spill Oil can be seen in ditches dug byTesoro. These ditches collected over 1,200 gallons of oil per week for months after the spill was discovered.