What is the procedure for determining the bulk reaction rate to undertake a water quality (constituent) analysis?
To start with it should be understood that there is no such thing as a typical bulk or wall reaction rate. Those values vary widely from system to system at different conditions. What can be done is perform a sensitivity analysis varying the reaction rates for multiple scenarios and plotting all the results on a single graph for multiple junctions.
As far as bulk decay, the first step in any chlorine study should be a bottle test. You should do a field study and collect chlorine residuals, run the model assuming zero wall demand and compare modeled vs. measured chlorine. Based in that adjust wall demands somewhat guided by the fact that wall demand is higher in unlined cast iron pipes and smaller pipes.
Steps for running a bulk reaction test
Note: It’s important to use very clean bottles. Any impurity can change the expected results.
Forum Discussion - Water Quality (Constituent) Analysis for a proposed water distribution network
Getting data and setting up for a Constituent Analysis in WaterGEMS and WaterCAD