Numerical models of phosphate esters in the Chattahoochee River

Abstract

A numerical model was constructed to assess the magnitude of organophosphoric acid triester sinks in the Chattahoochee River and to identify concentration patterns downstream of point source discharges. The model was built using WASP5 and supporting software packages. The model simulated mass transport of tri-butyl phosphate, tri (2-butoxyethyl) phosphate, and tri (2-chloroethyl) phosphate within a reach of the river bounded by Buford Dam and Northern Atlanta. Several potential mechanisms for the removal of the phosphate esters from the water column were considered. These were biodegradation, sorption to settling solids, volatilization, and oxidation by free radicals. Of the three phosphate esters considered by the model, tri (2-chloroethyl) phosphate was predicted to be the most resistant to degradation by natural attenuation processes. Tri (2- butoxyethyl) phosphate showed the most potential for degradation in surface waters. Biodegradation and sorption to settling solids were predicted to be the most effective processes for the removal of tri (2-butoxyethyl) phosphate. Concentration patterns at several locations downstream of point source discharges were predicted for the three compounds. Concentration patterns were found to be affected by the diurnal flow variation caused by the operation of two hydroelectric dams within the modeled reach.