The influence of two transport modes on the source identification is assessed with this test case. The first transport mode (i) represents an advection dominant transport with Pe = 50, and the second example (ii) is one of marginal advection transport with Pe = 1. The simulation parameters for the two transport cases are given in Table 1, while the fully implicit scheme with θ = 1 is used in all the simulations. The influence of the time step on the numerical solutions is assessed for three values of the Courant number, Cr=uΔt/Δx, namely Cr= 0.1, 0.5 and 1.0. Additional concentration data are provided at two observation points γ₁ and γ₂ that are located along x= 0.025 km for both transport modes.