“…The mathematical specification (1), (2) requires three independent dimensionless parameters, one of which is a removal rate, For any data fitting or validation, two further parameters For nondispersive (piston) flow, Ca = Cr. The concepts and interpretations of resident and flux concentrations have been discussed in detail by Brigham [1974•, by Kreft and Zuber [1978, 1979, and by Parker and van Genuchten [1984,1986]. Those researchers have noted that if C a satisfies an equation of the form (19), then so too does C r. (This is immediately apparent by noting that the differential operator (1-8/•) commutes with all of the operators in (19)).…”