You have been hired as a consultant for the Hanford DOE site in Washington state and you are reviewing the output from a groundwater model developed as part of an earlier study. The computed heads and pathlines from the model are shown below. You are asked what is the minimum travel time from the 200 west site to the Columbia river. Assume that the length of the flow path shown on the diagram is 20 miles. The head contours are in meters. The hydraulic conductivity is 150 ft/day and the porosity is 0.3. What is your answer?