Attention is given to the degree of primordial deuterium's astration through the continuous galactic processes of star formation and chemical evolution. Exact analytic solutions are given for galactic chemical evolution when infall of constant composition occurs at a rate, f(t), which is presently defined. Solutions are given for the linear model with instantaneous recycling and with constant return fraction R. The results suggest that Big Bang D/H was at least three times larger than the largest values observed in today's solar neighborhood, and even larger if matter falling into the disk is already astrated.