Modelling Of Contaminant Intrusion Flow Rate Into Water Distribution Systems

Untreated groundwater can intrude into water distribution systems through pipe leaks when negative pressure events occur inside drinking water pipelines. It is important to determine the magnitude of the possible intrusion event. The orifice equation is typically used for calculating intrusion inflow rates, which does not take into account the properties of the porous media surrounding the pipe. To estimate the intrusion flow rate that may enter through pipe leaks induced by negative pressure events, experimental and theoretical studies were conducted in this research. The impact of surrounding soil was an important consideration.In Chapter3, an experimental study was presented on the effect of porous media surrounding pipelines on intrusion flow rate for a circular orifice. Because untreated groundwater has the same flow characteristics as ordinary tap water, tap water was used in the experiments. Two orifice sizes and three kinds of porous media were studied in the experiments, and the effect of surface type, porous media and Reynolds number were studied. In Chapter4, an experimental study was present on the head loss in soil and the head loss through the orifice, and various factors were considered, including flow rate, orifice size and porous media. In Chapter5, an improved model was derived for predicting the intrusion flow rate for a circular orifice under steady-state conditions. The existence of the pipe itself formed an impervious surface in the seepage field, and its effect on reducing the flow area was incorporated in the modified model. The accuracy of geometry factor was improved in this model. The linear coefficient of flow rate in this model was reduced by40%to60%, and the quadric coefficient was reduced by70%to80%. In Chapter6, an experiment study simulating a buried pipeline was carried out to validate the accuracy of the improved modelThe findings of this study can be concluded as follows:(1) The presence of porous media could change the discharge coefficient which is dependent on orifice size, permeability of porous media, and flow Reynolds number.(2) The discharge coefficient of the orifice showing a zoning changes depending on the Reynolds number.(3) A discontinuity in the discharge coefficient was found at a large Reynolds number, and it is due to the separation of the fluid stream from the wall.(4) The intrusion flow rate is related to the pressure head difference between the inside and outside of the pipe, the orifice size, the soil permeability and the pipe diameter.(5) The improved intrusion model provides a good agreement with the experimental results.This study was conducted under steady-state conditions for a single circular orifice in a pipeline, and the erosion of soil particles around the pipeline was not considered. Future research may need to consider the pressure transients, the various forms of pipe leakage, the leakages distributed in the water distribution system and soil particles erosions around the pipeline.