First thing is to look at the chart on page 291 with a suggested plan for a 100km race. Notice that each week has a recommended distance. Even the Intensity weeks have this. Notice that on page 294 in the description of the Intensity week there are instructions for the intensity workouts, only there are these given as time and not distance. The other running workouts are given as distance/vertical. After the intensity workout volume you need to make up the recommended volume (distance and vertical) of training in this week with low intensity running.
I hope this helps.