First of all, "only" one pure speed session (via running) each week is plenty. There is really not a lot of sense in an endurance athlete trying to really drop his 30m sprint.
As far as SD for distance guys goes on a weekly basis, I usually approach it with 2-4 days of heavy lifting, a day with sprinting/striding as an adjunct to regular ESD work, and copious amounts of mobility work with emphasis on the hips.
The type of running I would advocate depends on the type of athlete.
For example, if he is a very strong runner with zero leg speed I might have him run 30-50m flying sprints, I might have him run 100m stides with the wind or down a slight grade (barely noticible as a grade…the slope of a football field).
If I'm working with more of a speed runner who lacks strength, I'd likely have him placing more emphasis on developing "neuromuscular firepower" through something like alactic hill sprints on big recovery or 100m strides into the wind. I also may consider at later points in the training cycles to include 150m sprint, float, sprint as well.
While the separation between the two athletes exists in my mind, and it is important to cater to and strengthen the weaknesses, this is not to say that I wouldn't have a strength guy run alactic hill runs, or a speed guy do 30m flying sprints, just that I would likely place a greater emphasis upon certain weak qualities.