We analyze numerical simulations of a second-order chemical reaction (Da = 1) in a fully developed turbulent plane channel flow at a low Reynolds number (Reτ = 180). The reactive plume is formed when a reactant A is released through a line source into the channel flow doped with reactant B. Two different inlet pre-mixing conditions and line source heights are considered. Direct Numerical Simulations (DNS) and Stochastic Fields (SF) methods have been used and compared for these different conditions. The results obtained using SF are sensitive to the particular value of the turbulent Schmidt number (ScT) selected to model the turbulent dispersion. It has been found that if a representative value of ScT extracted from DNS is used in the SF method, both DNS and SF, give similar results.