According to Google TDRW is short for Time Domain Random Walk
and I quote:
"It is shown here how a Time Domain Random Walk (TDRW) method can be inverted by deriving the sensitivities analytically. The calculations are very rapid and provide a precise evaluation of the descent directions followed by a Gauss-Newton optimizer. The method handles advection-dispersion + retention by matrix diffusion or sorption with first-order kinetics and proves its worth in all cases. Since analytical sensitivities are available, calculations are rigorous and allow discussing the inversion feasibility, the accuracy of the sought parameters, according to the predominant mechanism involved in the transport scenario."
It might be hard to believe but this makes a lot more sense to me than the application above, and clearly can be seen as the reason why the application was denied.