This data release documents the inputs and outputs for a coupled water-chloride mass balance model at Long Branch in Fairfax County, VA. Data inputs include daily measurements of various ecological conditions including precipitation, temperature, discharge and specific conductance. Output data include daily predicted values of discharge, chloride concentration, and volume for the different reservoirs hypothesized in the model. This data was used in support of “A 10-year continuous daily simulation of chloride flux from a suburban watershed in Fairfax County, Virginia, USA” by Jeffrey G. Chanat and Christopher A. Custer.