This report describes updates to the earlier developed groundwater availability model for the Hill Country portion of the Trinity Aquifer System, "by (1) adding the Lower Trinity Aquifer as another layer to the model, (2) revising the spatial distribution of parameters, such as recharge and pumping, and (3) calibrating the steady-state water level and river discharge conditions for 1980 and historical transient water level and discharge conditions for 1987 through 1997" (p. 1).