The WTC separations are all based on worst case estimates of the stability of wake vortices remaining as hazards after aircraft takes off or lands.
This is a good ad-hoc system but it can be extremely wasteful of resource if there is a crosswind that is effectively clearing the wake vortices in a few seconds yet the next aircraft sits for minutes because on a calm day the vortices may last longer.
Similarly, if there are parallel runways the vortices from one runway may interfere with aircraft on the parallel. Insisting on delays for aircraft using the same runway in that case will miss the hazard to aircraft operating on the parallel. Lots of research work has been carried out assessing these issues.
The potential cost to an airport in terms of reduced runway acceptance rates is huge. There are several laser based systems on the market that allow the vortices to be tracked and assessed so that only real hazards cause delays. Possibly the most advanced is WindTracer
WindTracer® for Airports · Lockheed Martin which also assists the forecasters with mesoscale forecasts. It is surprising that the take up of these systems is so low.
(I do not work with LM )