Pennington Seed: I would go with MVP from Turface. If they would like to call me I can do a site visit too, if they would like. Amy Mathews, Pennington Seed, Inc. 479-466-4983, firstname.lastname@example.org
UofA: I’d assume they could use whatever material composes the warning track as fill. If that’s too expensive, a pea gravel of similar sized particles could be used as fill, which would drain well, and then the track material could be placed over the gravel. I would be concerned with gravel coming to the surface it is not buried by a few inches of the track material. I suggest you contact some sports turf managers and get their opinion on this.
Russellville: We used sb2 gravel compacted. It works really well.
JACOBS: Clay mix with infield conditioner should be heavy enough to keep it from washing out provided you have 1.5% grade on fields or less.
DeQueen: Turface is the best material that I have used for this kind of drainage.